Recycling thermoset composite waste from the - Archipel

UNIVERSITÉ DU QUÉBEC À MONTRÉAL
RECYCLING THERMOSET COMPOSITE WASTE FROM THE AEROSPACE
INDUSTRY
THESIS
PRESENTED
AS PARTIAL REQUIREMENT
OF THE MASTERS OF CHEMISTRY
BY
STEFAN ANDJELIC
JUILLET 2014
UNIVERSITÉ DU QUÉBEC À MONTRÉAL
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UNIVERSITÉ DU QUÉBEC À MONTRÉAL
RECYCLAGE DE DÉCHETS COMPOSITES THERMODURC ISSABLES DE
L'INDUSTRIE AÉRONAUTIQUE
MÉMOIRE
PRÉSENTÉ
COMME EXIGENCE PARTIELLE
DE LA MAÎTRISE EN CHIMIE
PAR
STEFAN ANDJELIC
JUILLET 2014
ACKNOWLEDGMENTS
My time as a graduate student at UQAM has been truly a great experience. 1 would
first and foremost like to thank my director Professor Steen B. Schougaard, who welcomed
me into his laboratory. My progression at the academie level could not have been possible
without his help, as he has given me enumerable opportunities for which 1 am very grateful.
1 learned a great deal during my internship at the National Research Council Canada
(NRC: Boucherville, Quebec, Canada), thanks in part to both Nathalie Legros and Karen
Stoeffler, who greatly contributed to this project, and were my co-sponsors during my stay at
the NRC. 1 would also like to thank Lolei Khoun for her help and advice.
This work has been supported by the Consortium for Research and Innovation in
Aerospace in Quebec (CRIAQ) (identified as CRIAQ ENV -411 project), as weil as, the
industrial partners Bell Helicopter Textron Canada Ltd. (BHTCL: Mirabel, Quebec, Canada)
and Bombardier Aerospace (Montreal, Quebec, Canada).
I would also like to thank Judith Roberge from BHTCL, who allowed me to publish a
paper in SAE International, and present my project at the SAE AeroTech Congre ss &
Exhibition.
Finally, I would like to thank my family, fri ends, and co-workers for their support.
TABLE OF CONTENTS
LIST OF TABLES ..... .......... .... ............ .......... .. .. .............. .... .. .. .............. .. ....... .. ............ .... .. .... . ix
LIST OF FIGURES ... ... .. .... ......... .... .. ..... ...... ...... .. ..... ... ...... ........ ...... .... .. ... ... ........ ... ........... ...... vi
RÉSUMÉ ..... ... ...... ........... ... .......... ...... .. .... ...... .. ...... .... ............ ...... .... .. ....... ... .. ....... ..... ..... .. ....... . x
ABSTRACT .......... ..... ........ ..... .... ..... .. .. ....... ..... ......... ... ....... .... .... ... ..... ..... .... ........... ........ ....... . xii
CHAPITRE I
INTRODUCTION .. .. ....... .... ..... ... .......... ... ... ..... ...... ... .. ....... .. ... .. ... .. ...... ......... .. ..... .. ........ ......... .. 1
1.1
Context ............ .. .. ........ .. ...................... ..... ...... .. .. .. ...... .. ....... ...... ............... ........ ...... ........ . 1
1.2
Mec han ical Properties of Materials .... .... .. .. ............ .... .. .. ............... .. ...... .. ........ ............... 1
1.3
Composite Structural Materials ... ..... ... ....... .... ........ ... .. ...... ............ ......... ............. .. .......... 4
1.4
Res in Systems ............. ......... ... ..... ...... ..... .... .. ....... ...... .. .. ... .... ... ........ ..... ... ... ... ... ............ .. 8
1.5
Carbon Fi bers .... ..... .. .. .... ....... ... .... ....... ... .......... .... ..... .. .. ............. ...... ... .... ....... .... .. ... ...... 10
1.6
Carbon fiber 1 Composite market.. .. .. .... .. .. .......... .. .. ....... .......... .. .. .... .. .. .. ........ .. .. .......... . 13
1.7
The need to recycle .. ........ ........... .......... .. ...... .. .. .. .. .................... ................ .. .... ...... ........ 14
1.8
Challenges .... .... ..... ............... .. ..................... ..... ........ .. .. ...... .. ..... ... ....... .... ....... ....... ....... . 15
1.9
Recycling strategies ............ .. .. .. .. .................... .. ............ .... ........ ...... ........................ .. .... 15
1.9.1 Overview ... ...... .. ...... ... ..... .... ....... ..... .. ..... .... ....... .. .... ...... ... ..... ... ........ .... .. ... ....... ... 15
1.9 .2 Pyrolysi s Processing .. .................. .. ............ .. .. ......... .... .............. .. .... .. ........ .. ........ 16
1.9.3 The Fluidized Bed Process .... .. ........ .... .. .... .... ........ .................... .......... ............ ... 19
1.9 .4 Catalytic Conversion ... ...... .. .. ................ .. .. .. ........ ..
00 00 . . 0000 00 00 . . . . 0000 00 . . 00 . . . .
oo ..
00 . . . . . . .
21
1.9.5 The Supercritical Fluid Processoooo .......... .... .... oo .... oo .... .. .. .. oo .. oo ........ .. ...... .. oo .... .... 22
1.9.6 Other Available Technologies .. oo .. oo .. .. oo .. .. oo .... .. oo .......... .. oo .. oo oo oooo ...... .... oo .. oo oooooo oo24
1.10 Re-manufacturing Carbon Fiber Reinforced Thermoset Composites .. ...... ......
00 . . 00 . . . . . . .
25
1.1 0.1Overview .. oo ...... oo .... oo oo oooo oo oo .. ........ oo .. oo .. .......... ........ .. .... .. oo oooooooooo .. ........ oooooo .... oo .. . 25
1.1 0.2 Fabricating Recycled Carbon fi ber Mats .. oo .......... .......... oo .. ...... oo .. .. oo .. ................ 25
1. 10.3Wet lay-u p processing oo .... .... .. .. ........ .. .. oo .. oo ...... .. .. oo .. oo oooo .. .... .. oo .. oo .... oo .. .... .... oooo .. 26
IV
1.1 0.4Resin Transfer Molding .......... .......... .... ...... .. ... ... ... ...... .......... ..... .. ....... .. ... ... ..... .. 27
1.10.5 Infusion Molding ............. ......... ... .......... ... .... .. .. .. ... .... ....... .. ..... ... .... .... .. ... .. ....... .. 28
1.1 0.6Sheet Molding Compound (SMC) .. ... ....................... .. .... .... .. .............................. 29
1.11
Summary .. ... ... .. ... .......................... ......... ........... ..... .... ............ ... .... ... ... .. .... .......... ... ... ... . 30
CHAPITRE Il
EFFECT OF MORPHOLOGICAL, MECHANT CAL AND SURFACE PROPERTIES ON
THE WETTABILITY AND INTERFACIAL ADHESION OF RECYCLED CA RBON
FIBERS ................... .......... .. .... ....... .. ..... ..... ........ ... ..... ...... .. ... ...... ............ ... ... .................. ........ 3 1
2.1
Abstract ... .. ... .. ........... .............. ....... ....... ....... .... ........... .. ............. ........ ....... ........ ............ 32
2.2
Introduction ........ ..... ...... ...... ........ ...... ........ ........ ... .. .... ...... ..... ................... ....... ... .. .. ....... 33
2.3
Materials .. ... ............. ...... ............ .. ..... .... .... ........... .. ... ... .. ...... ............ ..... ... ..... ........... ..... 34
2.3 .1 Carbon Fi bers .... ....... ......... ........... ......... .. ... .... ........ ..... ... ........................ .. .. ..... .... 34
2.3.2 Resin .......... ..... ..... .... ... ....... ...... .. ..... .. .. ..... ... ... .... ... ...... .. .... .. ......... ..... ..... ........ ..... 35
2.4
Experimental ......... .... ... .. .... ........... ................... .................. ..... ... .......... .. ...... ..... ... .. ....... 35
2.4. 1 Characterization of Carbon Fiber Morphology ......... .. ............... ......................... 35
2.4.2 Characterization of Carbon Fiber Mechanical Properties ....... ... .... ... .. .. .............. 36
2.4.3 Characterization of Carbon Fi ber Surface Properties ........................ .. .... ....... .... 3 6
2.5
Results and Discussion ....... .. .... .. ....... .. .... .... ............... ......... ......... ............ .... ... .. ... ..... .... 3 8
2.5.3 Characterization ofCarbon Fiber Surface Chemistry ........ .... .................... .. ... ... .41
2.6
Conclusion .. .. .. ...... .. ..... ......... ....... ... ....... .... ......... ...... ..... ... .... ................... ......... ............ 50
2.7
Acknow ledgements .............. ....... ............ ... .......... .............. ... .. .... .. ... ... .. ....... ...... ... .. .. ... . 51
2.8
References ..... .. ............ .... ..... .. .. ...... ... ... ... ........ ........... ......... .... ...... ........ ................... .. ... 51
CHAPITRE III
CARDED RECYCLED CARBON FIBER MATS FOR THE PRODUCTION OF
THERMOS ET COMPOSITES VIA INFUSION 1 COMPRESSION MOLDING ... ....... ..... .. 54
3.1
Abstract ........ .. ..... ....... ................... .......... .... ... ............ .. ...... .... ..... ......... ... .. ..... ...... .... .... . 55
3.2
Introduction ........... ... .. .. .... ........ .. .. ............................................. .... ..... .. ...... ....... ............ 56
3 .3
Materials ... ..... .................... .... ....... .. .. .. ............. .... ... .... ... .... ............. .... ...... .... ... ............. 57
3.3.1 Carbon Fibers ... ....... ................................. ........ .. .. ........... ... ..... .... ................. .. ..... 57
3.3.2 Resin ........ .... ........................................................................... ...... ...................... 58
3.4
Experimental ...... .... ... ... .......................... .... .... ....... ..... ......................................... .. .. ..... . 58
3.4.1 Characterization of the Carbon Fibers ........................... .. ..... ............... .. ... .......... 58
3.4.2 Characterization ofthe carbon fibers 1 epoxy adhesion ................... ......... .. ..... .. . 59
v
3 .4.3 Carbon fi bers 1 epoxy compos ite plates fabrication ...................................... ...... 59
3.4.4 Characterization of the carbon fi bers 1epoxy composite plates .. .. ... .. ...... .......... 60
3.5
Results & Discuss ion ....... .. .. ......... .. ... ..... .. ............. .. .... ... .... ....... .. ... ........ ..... ..... .. .......... 62
3 .5.1 Characteri zation of the Carbon Fi bers ......... .. ..... ......................... ..... ........... .... ... 62
3.5 .2 Characterization of the carbon fi ber 1 epoxy adhesion ...................................... . 64
3.5 .3 Characterization of the carbon fi ber reinforced epoxy compos ite plates ........... . 66
3.6
Conclusio n ... ... .. .. .. ................. .... ..... ..... .... ..... ..... ..... ........ ...... .. .... ... ..... ...... ........... .. .... ... 7 1
3.7
Acknow ledgements ... ........... ... ..... ..... ... .... .. ....... ... ... .. ... .. ................ .. .... ... .............. ....... . 7 1
3.8
References .............. ...... .... ............. ........ .... ....................... ... .. ......... ....... ............... ......... 7 1
CHAPITRE IV
CONCLUS ION ..... .... ....... .... .. ... ....... ...... ...... ....... ... ... .. .. .... ... .. .. ..... .... .... .... .. ............................ 74
APP EN DIX A
SUMMARY .. ....... ...... ....... ....... ..... ............................. .......... .... .. .. ..... ................. .. .. ... .. ............ 76
A.l
Composite Waste Legislation ....... ........ ......................................... .................... .......... . 78
A.2
Polyphenylene Sulfide (PPS) Compos ites Reinforced with Recycled Carbon Fiber. ... 85
BIBLIOGRAPHY ...... .......... .. ....... ...... .... ... ........ ............... ... .................. .............. ..... .............. 92
LIST OF FIGURES
Fi gure
Page
1. 1
Ideali sed Stress-Stra in be hav io r of a ductile materi al under tension .. .................. 2
1.2
Typical stress-strain behav ior fo r brittle and ductil e materials ............................. 4
1.3
Typ ical stress - stra in relatio nship for composite materials, and their
components, undergo ing tensile testin g ........................... ................ ....... ... ..... .. .... 5
1.4
Externa ll oading on compos ite structura l materi a ls .............................................. 6
1. 5
Density (g/cm 3) of commo n structura l materi a ls .................. .. .................. ... .. ....... 6
1.6
Spec ifie tensil e strength (MPa cm 3 1 g) of commo n structura l materia ls .... .. ........ 7
1.7
Spec ifie tensile modulus (GPa cm 1g) of common stru ctural materi a ls .... .. ...... 7
1.8
a) C hemical Structure of a Typical Epoxy (Diglyc idyl Ether of Bispheno i-A),
and b) A ddition reactio n of am ine w ith epoxy groups ...... .. ................ .. .. .. ........... 9
1.9
Schematic representati o n of a cu red epoxy res in system (3 -D structure) ............. 9
1.10
U nit ce ll of Graphite ......................... .. .... .. ...... ..... .... .. ........ .. .............. ... .. .. ..... .. ... 10
1.11
C ross-section of PAN based Carbon Fibers .......... .. .... .. ...... .. .............. .. .... .. ....... . 1 1
1.1 2
Structure of a PAN based carbon fi ber at di ffere nt points during carbonization
and graphitization .... .. ... .... .. .. ..... .. .............. ... .. .. .................................................. 12
1.13
Reyno ld and Sharp ' s mecanis m for tens il e fai lure of PAN based carbon fibers 13
1.14
Carbon fiber demand by year and industry ................ .. ...... .. .. .. .. .. ...... .. .. .... ......... 14
1.15
Recycling strategies for thermoset structural composite waste .......................... 16
1.16
A general process flow diagram for pyrolysis processing .......................... .. ... .. . 17
1.17
A general process flow diagram for the fluidized bed process ........ .. .... ............. 19
1.18
A schematic of the fluidized bed reactor .......... .............. .. ........ .. .. .... .. .. .. .. .. .. ...... 20
1.19
A general process flow diagram for the catalytic conversion process .. .............. 22
3
VII
1.20
A general process flow diagram for the supercritical fluid process .................... 23
1.21
Wetlay Process for makin g recycled carbon fi ber mats ... ... ... .......... .. .. ........... .... 26
1.22
Carding process for making recyc led carbon fi bers mats ..... ........ .......... ........... . 26
1.23
A schematic representati on of the wet-lay process .. .. ...... .... ............ .. .. .. .. ...... ..... 27
1.24
A schematic representation of Res in Transfer Molding (RTM) .. .. ..................... 28
1.25
A schematic representation of infusion mol ding ................................................ 29
1.26
Schematic representation of the SMC process .. .. ...... .. ... .. .................... .... ........... 29
1.27
Schematic Representation of Compression Molding .......... .. ...... .... .................... 30
2.1
SEM micrographs of the recyc led carbon fibers from a) prepregs, b) tooling, and
virgin carbon fibers from c) Torayca® T700S ............... .. ................................... 39
2.2
Tensile modulus E (GPa) and maximum tensil e strength CJmax (MPa) of the
carbon fi bers ....................................................................................................... 41
2.3
20 point N 2 adsorption 1 desorption isotherms. Volume (cm /g) versus relative
pressure P/ P0 for the the recycled fi bers from a) prepreg and b) Tool ing ....... ... 43
2.4
Differentiai pore volume (cm 31Â/g) versus pore widths (Â) for the recyc led
fibers from a) prepregs, b) Tooling, and virgin fibers from c) Torayca® T700S
and d) Panex® 35 . ....... .. ... .. ... ... ..... ... .... ......... ....... ............................. ........ .......... 44
2.5
XPS survey and high resolution C 1s spectra for the recycled carbon fi bers from
a) prepreg, b) tooling, and virgin carbon fibers from c) Torayca® T700S ....... ..47
3.1
Schematic representation of the infusion 1 compression moulding process ....... 60
3.2
Geometry and position of the test specimens eut from the carbon fi bers 1 epoxy
plates ..... ....... .... ... .. ... .. ..................... ... ..... ...................... ..... ... ..... .. ........... .. ... ....... 61
3.3
SEM micrographs ofthe recycled carbon fibers from a) prepregs, b) too lin g ... 63
3.4
Tensi le modulus E (GPa) and max imum tensile strength CJmax (MPa) of the
recycled carbon fibers from prepregs and tooling, and virgin carbon fibers from
Toray T700SC . ... ....... ..... ..... .... ...... .......... ....... .. ... ... .. .... .. ... ... .... .... ... .. .. ... ...... .. ... . 64
3.5
Force (N) versus Embedded Length (!lm) of the recycled carbon fibers from
prepregs for the microdroplet test. .. ................................ ...... .... .. ........................ 65
3.6
Variation of composite density along the injection direction for the carbon fibers
1 epoxy plates . .. ...... ......... .. .. .. .. ............. ... ........ ... ............. .... ..... ... ... ... .................. 67
3
VIII
3.7
SEM micrographs of the polished cross-sections along the injection direction of
plates P3 and T3 ............................................................. .. .................. ......... ....... 68
3.8
Tensile modulus E (GPa) of the carbon fi bers 1 epoxy plates ............................ . 69
3.9
Maximum tensile strength O' max (MPa) and elongation at break eb (%)of the
carbon fibers 1 epoxy plates ... .... .............................................. .... ....................... 70
3.10
Flexural modulus E (MPa) and flexural strength at yield O'y (MPa) of the carbon
fi bers 1 epoxy plates . ...... .... .. .............. .. .................... .. ........................................ . 70
LIST OF TABLES
Page
Tab le
1.1
Characterization ofthe liquid and gas pyrolysis products from sheet molding
compounds composed of polyester and glass fi bers . ...... .... ... ... .. .... ... ............ .... . 18
1.2
Chemical composition of hydrocarbon product recovered from catalytic
convers ion .......... .. ................ ... ...... ....... ........... ... ............. ....... .... ..... ... .... ... ........ .. 22
1.3
Chemical composition of decomposed polymers produced by the semicontinuous supercritical fluid pro cess ....... ....... .. .. ... .. ..... .. ..... .... .. .. .. ........ ... ...... ... 24
2.1
Processing properties of the infusion grade epoxy PRISM™ EP2400 produced
by Cytec Engineered Materials .... ...... ......... ..... .... .. ....... ..... .............. .......... .. ....... 3 5
2.2
Summary of Carbon Fi ber Morphology ......... .. .. ... ..... .. .... .... ... .. ........ .. .. ....... .... ..40
2.3
Spec ifie surface area (m /g) of the carbon fibers .... .... .... .. ................ ........ .. ........ 42
2.4
The surface elemental compositions (%) based on the XPS survey scans of the
carbon fi bers ... ... ... ............ .... .............. ... ... ....... ... ........... .. .... ......... ... ... ... ............. 44
2.5
Curve fitting results for the C 1s high resolution scans of the carbon fi bers ... .. .46
2.6
Surface free energy components (mN 1 m) of the probing liquids .... .. .............. .. 48
2.7
Surface free energy components (mN 1 m) ofthe carbon fibers .. .. ...... ...... .... .. ... 48
2.8
Interfacial shear strength (r) of th e carbon fibers ............................. .. .. .. .... .. .. .. .. 49
3.1
Properties of the infusion grade epoxy PRISM™ EP2400 produced by Cytec
Engineered Materials ....... ...................... ... ............. ... .. .. .... .................................. 58
3.2
lnterfac ial shear strength ('r) of the recycled carbon fi bers fro m prepregs and
tooling, and virgin carbon fi bers from Toray T700SC ... .... ...... .. ........ .... .. .. .. ...... 65
3.3
A List of the carbon fibers 1 epoxy composite plates produced by infusion 1
compress ion moulding ........... .... ..... ......... .. ....... ......... .. .. .. .. ..... .. .... .. ...... ..... ... ...... 66
2
RÉSU MÉ
L'utilisation croissante des compos ites thermodurci ssables renforcés de fibres de
carbone (CFRPs), dans l'industrie aéros patiale, génère un e quantité importante de déchets
compos ites. Actue llement, la grande maj orité de ces déchets compos ites sont envoyés dans
les sites d'enfo ui ssements. Donc, le recyclage des CFRPs permettrait de réduire la quantité de
déchets compos ites et de récupérer des fi bres de carbone.
Dans ce travail, les fibres de carbone recyclées "Prepreg" et "Tool ing" ont été
récupérées des CF RPs générés par l'industrie aéronautiqu e canadi enne avec un procédé de
pyrolyse, à l'éche ll e commerciale, de Materials Innovation Technolog ies.
Les propriétés morpholog iques, mécaniqu es et de surface des fibres de carbone
recyclées ont été caractéri sées par les techniques suivantes; microsco pie électronique à
balayage (MEB), mesures de densité par pycnométrie, tests de mi cro-traction, ana lyse BET,
spectroscopie de photoélectron s rayons-x (XPS), analyse de mouill abilité par l'angle de
contact dynamiq ue et l'adhérence interfac ia le par des essais de mi cro-goutte lettes avec un e
rés ine époxy. Les fibres de carbone recyclées conservent une bonne tenue mécanique et
adhés ive, de qua lité comparable à des fi bres de carbone neuves. Cepend ant, le traitement par
pyrolyse a modifié le urs propriétés de surface par l'é limination de la rés in e et de la couche de
" Sizing", révélant ainsi les topographies de surface.
Le chapitre 1 couvre la théorie sur les matériaux compos ites structu raux, les systèmes
de rés ine et les fibres de carbone. De plus, des technologies de recyclage des CFRPs so nt
présentées et évaluées. La pyro lyse a été déterminée comme la technolog ie la plus
économiquement viable, car ell e permet de récupérer des fi bres de carbone de hautes qualités.
Enfi n, plusieurs méthodes de re-fabrication des composites thermodurcissables utilisant les
fi bres de carbone recyc lées ont été exp lorées.
Le chapitre Il présente les résultats de l'effet du traitement par pyrolyse sur la
mouillabilité et l'adhérence interfaciale des fibres de carbone recyclées avec une résine
époxy. La moui ll abilité et l'adhérence entre la surface des fi bres de carbone recyclées et la
résine époxy sont principalement affectées par les interactions acide 1 base de Lewis des
groupes fonctionne ls oxygénés de surface, ainsi que, par l'encastrement ("Interl ock")
mécanique. L'encastrement mécanique semble être le paramètre prédominant, car les fibres
striés de "Prepreg" ont une adhésion interfaciale, avec une résine époxy, plus élevée que les
fibres lisses de "Tooling". Par conséquent, les topographies ont été jugées extrêmement
Xl
importantes pour prédire la performance des composites re-fabriqués avec des fibres de
carbone recyclées.
Le chapitre III présente une méthode de re-fabrication des composites
thermoducissables contenant des fibres de carbone recyclées. Les fibres de carbone recyclées
ont été réintegrées dans de nouveaux composites thermodurcissables en fabriquant des
plaques résine époxy 1 fibres de carbone recyclées. Un procédé de cardage suivi d'un
traitement par ultrasons permet de fabriquer des mattes de fibre de carbone recyclées, qui
sont alignées de façon aléatoire. Ces mattes ont été utilisées pour fabriquer des plaques résine
époxy 1 fibres de carbone recyclées, avec des fractions volumétrique de fibre jusqu' à 40 %,
par le moulage infusion 1 compression.
Les propriétés mécaniques des plaques composites ont été évaluées par des essais de
traction et flexion. Les plaques composites qui contiennent des fibres de carbone recyclées
ont des propriétés mécaniques comparables à celles qui contiennent des fibres de carbone
neuves. Ce travail démontre l'énorme potentiel de re-fabrication des composites
thermodurcissables à partir fibres de carbone recyclées. Ces matériaux peuvent être utilisés
dans des applications adaptées à l'industrie aérospatiale ou dans d'autres marchés.
ABSTRACT
The increasing use of carbon fiber reinforced thermoset composites in the aerospace
industry has generated a significant amount of manufacturing and end of life waste.
Currently, the vast majority of this waste is sent to landfills, as such the reycling of carbon
fiber reinforced thermoset composite waste aims to reduce its disposai in landfills, and to
recover the potentially valuable recycled carbon fi bers.
In this work, chopped recyc led carbon fibers from prepreg and tooling were recovered
from carbon fiber reinforced thermoset composite waste generated by the Canadian aircraft
industry, using Materials Innovation Technologies commercial scale pyrolysis process. The
morphological, mechanical and surface properties of the recycled carbon fibers were
characterized
by
scanning electron
microscopy
(SEM),
density
measurements
by
pycnometry, micro-tensile testing, BET analysis, x-ray photoelectron spectroscopy (XPS),
wettability analysis by dynamic contact angle measurement and interfacial adhesion with
epoxy resin by micro-droplet testing. The recycled carbon fibers appeared relatively
undamaged, exhibiting a comparable mechanical and adhesive performance to virgin carbon
fibers. However, pyrolysis processing altered their surface properties by effectively removing
resin and sizing, thereby revealing surface topographies.
In Chapter I, a background is provided examining composite structural materials, resin
systems, and carbon fibers. In addition, recycling technologies for carbon fiber reinforced
thermoset composite waste are identified and evaluated. Fiber reclamation was determined to
be the most economically viable technology, as it can recover potentially valuable recycled
carbon fibers. Finally, severa! methods for re-manufacturing thermoset composites using
recycled carbon fibers were explored.
XIII
ln Chapter II, the effect of pyrolysi s processmg on the wettability and interfacial
adhesion of recycled carbon fibers with epoxy resin is evaluated . Wetting and interfacial
adhesion between the surface of the recycled carbon fi bers and epoxy res in were fou nd to be
predominantly affected by Lewis acid 1 base interactions of oxygenated surface functional
groups, as weil as, by mechanical interlocking. Mechanical interlocking appeared to be the
more important parameter, as the striated prepreg fibers out-performed the smooth tooling
fi bers in interfacial adhesion with epoxy resin. Therefore, surface topographies were found to
be extremely important when predicting the performance of re-manufactured composites
containing recycled carbon fibers .
In Chapter III, the recyc led carbon fibers were re-manufactured into new thermoset
composites by reintegrating them as chopped fiber reinforcement in epoxy plates. A cardi ng
process fo ll owed by an ultrasound treatment produced randomly aligned recycled carbon
fiber mats. These mats were used to fabricate epoxy 1 recycled carbon fiber plates, with fiber
vo lume fractions up to 40 vol. %, by infusion 1 compression molding. The mechanical
properties of the composite plates were evaluated by tensile and flexural testing, and were
found to be comparable to an equivalent containing virgin carbon fibers .
This thesis confirms the huge potential of re-manufacturing thermoset composites from
recycled carbon fibers, as they exhibited similar performance to virgin carbon fibers . Such
materials might be suitable applications in the aerospace industry or in other markets.
CHAPITRE I
INTRODUCTION
1.1
Context
The difficult issue of recycling thermoset structural composites has been the subject of
much investigation over the last 15 years, and on a large scale, is still an unsolved problem.
Thermoset structural composites have been used in aircraft components for many years, as
they significantly reduce aircraft weight and fuel consumption . Currently, composite waste
coming from the aerospace industry is either ground up into fillers , incinerated, or digested
using environmentally questionable technologies; however, the vast majority of composite
waste in North America is sent to landfills. Aircraft manufacturers are thus under serious
pressure to reduce waste through recycling or reuse, affecting both in-process waste and endof-life disposai. It is therefore important to continue research on the thermoset structural
composite recycling in order to become more environmentally friendly.
1.2
Mechanical Properties of Material s
Structural
materials are subject to
extemal
loadin g during
use. Therefore,
understanding how a material deforms or breaks is critical in ensuring a stable structure. The
re lationship between stress and strain reveals many im portant mechan ical properties as
dep icted graphically in Figure 1. 1 [1, 2].
2
Necking
Stra in Hardening
Stress
Fracture
Tensite Modutus = Rise 1 Run
Plastic Deformation
Strain
Figure 1.1 Idealised Stress-Strain behavior of a ductile material under tension [2].
In order to compare specimens of different sizes, external loads are calcu lated per unit
area. Force divided by area is called stress, and is measured in pressure units (Pa). In tension
and compression, the area is perpendicular to the external load, wh ile in shear or torsion, the
area is perpendicular to the axis of rotation. Stress is calculated by:
Πor
Where
force and
Œ
F
r =-
Ao
(1.1)
(Pa) is the tensile or compressive stress, r (Pa) is the shear stress, F (N) is
2
A 0 (m )
is the area.
Under tension and compression, the material deforms and elongates. In order to
compare specimens of different lengths, strain is measured as a change in length divided by
the specimen ' s originallength. Strain is calculated by:
!J.L
e =-
Lo
(1. 2)
Where e is the strain, !J.L (m) is the change in length, and L0 (m) is the ori ginal length .
Strain is often expressed as a percentage.
3
Material s can undergo two types of defo rmation, either elastic or plastic. Elastic
deformati on is reversible and non-permanent, whil e pl astic deformati on is irreversible and
permanent. In tensil e testing (Figure 1.1 ), when the deformati on is e lastic, the slope of the
stress-strain curve fo llows Hooke's law, defin ed as:
CJ
= Eê
(1.3)
Where E is Young's modulus a lso known as the modulu s of elasticity.
The fo llowing properti es can be a lso be obtained by th e re lati onship between stress and
strain of a materia l un der tension (Fig ure 1.1):
Tensile Strength: T he tens il e strength is also known as the ultimate strength, and
corres ponds to the max imum ten sile stress a material can withstand under tension. Tensile
strength is generally expressed in uni ts of MPa
=
106 Pa
Yield point: If the stress is too large, Hooke's law no longer applies, as stress is no
longer proporti onal to strain. This is called the y ield point, and it occurs when the material
begins to deform plastically.
Yield strength: The Yi eld strength corres pond s to the stress at the y ie ld po int.
Structura l mate rials are des igned to undergo onl y e lastic deform ation during use. Therefore,
in many cases, the yield strength is a more important parameter than the tensil e strength.
Tensile Modulus: The tensile mod ulus measures the stiffness of a material. lt ts
defined as the slope in the elastic region of the stress-strain curve, and corresponds to
Young' s modulus. Tensile modulus is generally expressed in units of GPa = 109 Pa
Toughness: Toughness is the ability of a material to deform plastically w ithout
fracturing . It corresponds to the area un der the plastic region of the stress-strain curve.
Resilience: Resilience is the capacity of a material to deform elastically. It corresponds
to the area und er the elastic region of the stress-strain curve.
4
Ductility: Ductility is the ability of a material to defo rm w ithout fracturing. lt
corresponds to the maximum strain before fracturing (maximum elongation). lt is th e
opposite of brittleness.
T he behav ior of materials can be broad ly classified into two categor ies; brittle and
ductile, as shown in Figure 1.2 [3, 4]. Ductile materia ls exhi bit large strains before fracturing,
white brittle materials fracture at much lower strains. The yie ld region for ductil e materia ls
takes up the majority ofthe stress-strai n curve, whereas for brittle mater ials, it is nearly nonexistent. Additionally, brittle materials have re lative ly hi gh tensil e mod uli and strengths
compared to ductil e materials.
Stress, cr
Brittle
Ductile
Strain, E
Figure 1.2 Typical stress-strain behav ior for brittle and ductile materials [3, 4].
1.3
Compos ite Structura l Materia ls
Compos ite structural materials consist of a matrix, usually a po lymer based resm
system, whi ch encapsulates reinforcing fibers [5 , 6]. The purpose of the matrix is to bi nd
reinforcing fi bers together, and to transfer externat loads onto them, producing a structurally
sound materia l. Additionally, fill ers and additives may be added fo r various purposes.
Common reinfo rcing fi bers include carbon, glass, and aramid fi bers; whit e, res in systems
include both thermoplastic and therrnosetting resins. As shown in Figure 1.3, reinfo rcing
fi bers have exceptional strength and stiffness, and undergo elastic deformation (brittle) under
externat load; whit e res in systems have poor strength and stiffness, and undergo plastic
5
deformation (ductile). Thus, the properties of composite structural material s depend on both
reinforcing fibers and resin matrix , and are determined by [5 , 6]:
1.
The mechanical properties of the reinforcing fi bers.
2.
The mechanical properties of the resin matrix.
3. The volumetrie ratio between reinforcing fibers and resin matrix.
4.
The geometry and orientation of the reinforcin g fibers.
5.
The interfacial adhesion between reinforcin g fibers and res in matrix.
Reinforcing Fiber
Co mposite Stru ctural Materi al
Resin
Strain
Figure 1.3 Typical stress - strain relationsh ip for composite material s, and their components,
undergoing tensile testing [6].
As shown in Figure 1.4, there are four main external loads that composite structural
materials need to withstand ; tension, compression, shearing and flexion. The response of
structural composite materials to tensile loading depends on the strength and stiffness of the
reinforcing fibers. On the other hand, their response to compressive loadi ng depends on the
stiffness and adhesive properties of the resin matrix; and to shear loading, on the ability of the
resin matrix to transfer stresses across the material. Finally, flexural loading is a combination
oftension, compression, and shearing.
6
Tension
Compression
Shearing
Flexion
t
Figure 1.4 Externalloading on composite structural materials [6].
Composites structural materials have been used in aircraft design for many years, as
they significantly reduce aircraft weight and fuel consumption. Carbon fiber reinforced
thermoset composites, also known as carbon fi ber reinforced plastics (CFRPs ), the main
foc us of this thesis, are characterized by the ir excellent mechanical properties, as weil as low
densities compared to traditional structural materials, as shown in Figure 1.5-1 .7.
8
•
6
3
•
2
1
•
•
•
•
1
Woods Al. Alloys ntanium
Steels
E·Giass S·Giass Aramid HS Carbon lM Carbon
Composite Composite Composite Composite Composite
Figure 1.5 Density (g 1 cm 3 ) of common structural materia ls [6].
7
Woods Al. Alloys Titanium
Steels
E-Giass S-Giass Aramid HSCarbon lMCarbon
Composite Composile Composite Composite Composite
Figure 1.6 Specifie tensile strength (MPa cm3 1 g) of common structural materials [6].
120
110
100
en
:::>
i;
0
:2::
~
90
80
·;;;;
70
1-
60
.,c:
'-'
.,c.
·;:;
50
Cl)
40
30
20
10
•
•
•
•
0
Woods Al. Alloys Titanium
Steels
1 1
1
E-G\ass S-Giass Aramid HS Carbon lM Carbon
Composite Composite Composite Composite Composite
Figure 1.7 Specifie tensile modulus (GPa cm 3 1 g) of common structural materials [6].
8
Finally, structural composite material s can be produced through fil ament winding, tape
winding, pultrusion, compression molding, vacuum bagging, liquid mo ldin g and injection
molding of fiber pre-fo rms w ith resi n systems [5, 6].
1.4
Res in System s
Res in System s util ized in structura l compos ites require adequate mechani cal, adhes ive
and toughness properties, as weil as, res istance to environmental degradati on. The two main
types of res in systems are thermopl astics and therm osets [5-7]. When heated, thermoplastics
soften and eventually melt, hardenin g again w ith coo ling. In theory, me tting and hardening
can be repeated as often as desired w ithout any adverse effects on material properties.
Exampl es ofthermoplastics include; polyethy lene (PE), polypropy lene (PP), po lyamide (PA),
polyethylene terephthalate (PET), po lypheny lene sulfide (PPS), polyether ether ketone
(PEEK) and polyether imide (PEI). Therm osets are di fferent fro m thermoplastics, as they
require curing, causin g the po lymer cha ins to cross-link and harden. Curin g occurs when
resin and hard ener, or res in and catalyst, are mixed together and undergo a non-reversible
chemical reaction. Once cured, thermosets wi ll not me lt if heated again, although above the
glass transition temperature (Tg), the mechanical properties w ill change sign ificantly, as the
mol ecular structure c hanges from that of a ri gid crystalline polymer to a more fl ex ible,
amorphous po lymer. T hi s causes the stiffness of the res in to drop sharply. Th e most commo n
thermosets inc ludes unsaturated polyesters, epoxies, vinyl esters and pheno lic res ins.
Epoxies are by far the most w idely used res in system, constituting over 90 % of ali
CFRPs [7]. Epoxies out-perform most other resin systems in tenns of mechanical and
adhesive properties, as weil as, resistance to environmental degradati on. They are extensively
used in high performance appl ications such as aerospace, defence, and sporti ng goods. A
typical epoxy mo lecule is presented in F igure 1.8a [6].
9
a.
CH -CH-CH - 0
\1
~
2
0
J
J
'---...J
0-CH -CH -
'---...J
2
\1CH
2
0
b.
Figure 1.8 a) Chem ical Structure of a typical Epoxy (Diglyc idy l Ether of Bispheno i-A), and
b) Additi on reacti on of amine with epoxy groups [6].
Epoxy mo lecules are long cha in structures with reactive epoxy gro ups at e ither end . In
the spec ifie case of Diglyc idyl Ether of Bispheno i-A, th e absence of ester groups (s uch as in
viny l esters) means that they are water res istant. The two ring groups of the Bispheno i-A
moiety are capable of absorb ing both mechanical and thermal stresses better than linear
polymers. As shown in Figure 1.8b, when curing epoxy res in with an ami ne hardener, the
epoxy and amine groups react by hi gh y ie ld addit ion reaction w ithout any by-products. T his
form a compl ex three-dimensiona l structure as illustrated in Figure 1.9.
~
)
EpoxyMole<ule
Armne Molecule
Figure 1.9 Schematic representation of a cured epoxy resin system (3-D structure) [6].
10
1.5
Carbon Fibers
Carbon Fibers are used as reinforcing material in structural composites because they
exhibit: high strength and stiffness, low density, and resistance to hostile environments [5 , 6,
8-10]. The atomic structure of carbon fibers is similar to that of graphite (Figure 1.10). It
consists of graphene sheets that are arranged in a hexagonal pattern . This forms basal planes
that are aligned along the fiber axis, which interact with each other via weak Van der Waal
bonding [8-1 0]. Carbon fi bers require approximately 198-594 MJ 1 kg of manufacturing
energy to produce [7].
j~~ r~
c~~
c
Figure 1.10 Unit cel! of Graphite [8].
Even though they are used interchangeab ly, there is a difference between carbon and
graphite fi bers [8-1 0].
The difference lies in the way the graphene sheets interlock. In
graphitic fibers , the graphene sheets are stacked parallel to one another in a regular fashion ,
and contain upwards of 99 wt. % of carbon . In carbon fibers, the graphene sheets are
randomly folded or crumpled together, and con tain upwards of 92 wt. % of carbon. Graphitic
fibers tend to have a much higher tensile modulus, while carbon fibers tend to have a much
higher tensile strength. Graphitic fibers are more expensive because they require higher
processing temperatures.
11
Carbon fi bers are produced by 3 types of precursors: rayon, polyacrylonitrile (PAN),
as weil as, isotropie and liquid crystalline pitches [5 , 6, 8-1 0]. This di scussion will be limited
to PAN based carbon fibers, as they are common ly used in the aerospace industry due to their
high tensile strength. They consist ofturbostratic graphite with basal planes aligned along the
fiber axis . Turbostratic graphite corresponds to a hi ghly oriented structure formed by para llel
layers of condensed hexagonal rings having no three-dimensional order [8-1 0] . This fonns a
microstructure remini scent of on ion skin, and is depicted on Figure 1.11 .
Figure 1.11 Cross-section of PAN based Carbon Fi bers [8-1 0].
PAN based carbon fibers are manufactured by controll ed pyrolysis of stabilized PAN
precursor fibers [5 , 6, 8-10]. PAN precursor fibers are atactic, linear polymers contain ing
highly polar nitri le pendant groups [9]. The transformation of PAN precursor fibers into
carbon fi bers consists of severa! steps: stabilization, carbonization, and surface treatment [9].
PAN precursor fibers are first stabilized by an oxidation process, at a temperature of
about 200 to 400
oc in air [9], where the linear PAN mol ecules (thermoplastic) are converted
into a cyclic structure (thennoset). Cross-linking of the polymer networks ensures that the
fi bers do not melt during processing. The next step is carbonization [9, 11 ], where the
stabilized fibers are heated to temperatures ranging from 300°C to 1500°C in an inert
atmosphere, in order to remove hydrogen, oxygen, nitrogen, and other non-carbon elements.
12
The carbonized fibers can be further graphitized at an even higher temperature up to around
3000 °C, to achieve even higher carbon content and higher tensile modulus, at the expense of
tensile strength, in the fiber direction . The structure of PAN based carbon fibers at different
points during carbonization and graphitization is shown on Figure 1.12 [11 ]. Finally, the
relatively inert surface of carbon 1 graphite fi bers undergo surface treatment [9, Il] , to
improve their adhesion to resin systems. The fibers may be etched using oxidizing agents
such as chlorine, bromine, nitric acid or chlorates. Carbon fibers are also subjected to sizing.
Sizing involves the addition of an epoxy coating, or other type of resin, onto their surface.
This process allows thousands of fibers to stick together producing a single filament known
as a tow. Furthermore, s izing prevents fiber abrasion and damage, improves handling, and
provides an epoxy compatible surface. The tows are wound onto a spool, where they are
stored until they are used during composite fabrication .
Figure 1.12 Structure of a PAN based carbon fi ber at different po ints during carbonization
and graphitization [ 11].
The properties of carbon 1 graphite fi bers are affected by many fact ors such as
crystall inity, crystallite distribution, orientation of the graphene sheets, carbon content, and
the amount of defects [9, 11 ]. Carbon fi bers can be classified as: ultra high modulus (> 500
13
GPa), hi gh modulus (> 300 GPa), intermediate modulus (> 200 GPa), low modulus ( 100
GPa), and hi gh strength (> 4 G Pa) carbon fi bers.
As shown in Figure 1. 13, PAN based carbon fi bers break by the brittle-failure
mechani sm proposed by Reyno lds and Sharp [8, 9]. T he crystallites present in PAN based
carbon fibers are not hi ghly aligned, and mi sori ented crystallites are common. When a stress
is appli ed parallel to the fib er ax is, th e crysta llites a lign until their movement is restricted by
the mi sori ented crysta llites. If there is suffi c ient stress, the mi sori ented crysta llites will
rupture. Wh en the size of the ruptured crystal lites (perpe ndi cul ar to the fi ber axis) is larger
than the critical fl aw size, crack propagati on leads to catastrophic fa ilure, i. e. the fiber breaks .
l
Stress
1
Misonented crystalli te
llnkmg two crystall ites
parall et to the fi ber
axis
Tensite stress causes
basal plane rupture in
L, direction
Catastrophic rupture if
crystallite size > critical fl aw size
Figure 1.13 Reyno ld and Sharp ' s mecanism fo r tensile fa ilure of PAN based carbon fibers
[8, 9] .
1.6
Carbon fi ber 1 Compos ite market
In the past decade, the use of thermoset structural compos ites, and more specifically
carbon fibers rei nfo rced pl astics (CFRPs), increased significantly in aerospace with the
development of the Boeing 787 Dreamliner and the A irbus A380 programs contai ning
approximate ly 50 wt. % and 20 wt. % of CFRPs respectively [7, 12]. They are also being
incorporated in a multitude of other prod ucts, such as sailboats and consumer goods. A nnual
14
global sales of CFRPs were $13 .6 Billion in 2010, and will increase to over $25 Billion by
2025 [13].
The carbon fiber market has been growing at a steady rate of 10 to 15 % annually [7]. In
2011, the global demand of carbon fiber tow rose to 45,800 tons. The aerospace industry
accounted for 6,410 tons representing approximately 15 % of the carbon fi ber market [ 14].
Carbon fiber demand by year and industry is depicted graphically in Figure 1.14 [15].
111 2009 1!1 2010 1!1 2011
02015 02019
140,000 ..-- - - - - - - - - - - - - - - - - - - - - - - - - - - ,
~
120,000
-g
100,000
:ê.
Cl)
~
80 ,000
0
êii
s:J
u::
60,000
c::
40 ,000
t5...
20,000
0
s:J
o L.. ..LJ_L_. . . .~~Aerospace
Consumer
lndustrial
Total
Industries
Figure 1.14 Carbon fiber demand by year and industry [15].
1.7
The need to recycle
Although thermoset structural composites present numerous advantages, their
increasing use generates a significant amount of composite waste estimated at 3,000 tons per
year in North America and Europe [16]. This waste includes out-of date prepregs,
manufacturing cut-offs, testing materials, production tooling and end-of-life components [12,
17]. Additionally, 8,500 commercial aircrafts will be decommissioned by 2025 , containing
approximately 20 tons of CFRPs per aircraft [12]. Currently, the vast majority of composite
waste is sent to landfills, raising questions about waste generated from manufacturing and at
end-of-life, especially in the aircraft industry.
15
Environmenta l concern s have lead to stri ct management conditions with respect to
composite waste, especially in the European Union (EU). Since 2004, the Landfi ll Directi ve
(1 999/3 1/EC) [18] has rendered the di sposai of compos ite waste to landfi lls illegal in many
EU countri es. Meanwhil e, extended producer responsibility has set recycling targets for many
types of waste. One important example is the end of life vehi cle di rective (2000/53/EC) [ 19],
which states that after 2015 ; only 5 wt.% of an end-of- li fe vehi c le can be sent to landfills. In
North America, there is currently no legislati on to curtail compos ite waste di sposai.
However, a few developments have recently been made by certain prov in cial governments,
such as the province of Quebec (Canada), whi ch has increased landfilling fees. A detailed
ana lys is of co mpos ite waste legislatio n is provided for in the appendix. The increas in g
legislati on on compos ite waste management requires the establishment of recyclin g routes to
ensure proper confo rmity w ith upcoming regul atio ns.
In addit ion to the legislative " push" factor, another dri ving force for recyc lin g
thermoset structural compos ites is recovering recyc led carbon fi bers, which reqUi res
approximately 10 times less manufacturin g energy th an virgin carbon fi bers [1 2].
1.8
Challenges
Thermoset structural co mpos ites are inherently di ffic ult to recycle due to their complex
compos ition; as they are a mixture of re info rcing fi bers, polymer resin, as we il as, additives
or fill ers. Moreover, they are often manufactured in com bination with other materi als. For
examp le, they may contain honeycomb or foram cores to reduce weight, metal inserts to
fasten onto other parts, and paint. Finally, in contrast to thermoplastics which can easily be
re-me lted, the cross-linked structure ofthermosets prevents re-molding [12, 17].
1.9
Recycling strategies
1.9 .1
Overview
There are two ma111 technological families for thermoset structural composite
recycling: mechanical grinding and fiber reclamation (Figure 1.15) [12, 20]. Mechanical
grinding consists of breaking down scrap composites by shredding, crush ing, or mi l ling, and
- -- -- --
-- - - - -- - - - - - - - - - - - - - - - - - - - - - -- - --
----------------,
16
then separating the fragments into powdered (rich in resin) and fibrous (rich in fibers)
products that can be used as fillers in new composites, artificial woods, asphalt, cement and
other applications. Fiber reclamation consists of employing either a thermal or chemical
process to break down thermosetting resin, thereby freeing the fibers. Additionally, energy
and chemicals can be recovered from the by-products. Fiber reclamation is the preferred
method for recyc ling CFRPs because high quality recycled carbon fibers can be recovered,
producing a potentially more va1uable product. Virgin carbon fibers require 198-594 MJ 1 Kg
of manufacturing energy, while recycled carbon fibers require only 11 -36 MJ 1 kg [12].
Therefore, fi ber reclamation will be the focus of this thesis, as it is the more economical1y
viable process if app lications can be found for recycled carbon fi bers. The following sections
will take a detailed look at different fiber reclamation techniques available for thermoset
structural composites, and more specifically CFRPs.
Recycling Processes for
Thermoset Composites
1
l
Il
T hermal
l
Pyrolysis
1
1
l
1
Jl Fluidized bed J
Chemical
1
1 Mechanical [
l
Solvol~s is
1
1
Mechanical Grinding J
- Catalytic Conversion
- Supercritical Fluid
Processes allowing for carbon fiber reclamation
Figure 1.15 Recycling strategies for thermoset structural composite waste [ 12, 20].
1.9.2
Pyrolysis Processing
Pyrolysis processing is current1y the most mature method for recycling thermoset
structural composites, as it can recover high quality recycled carbon fibers from a diverse
feed stock [12, 20]. As shawn in F igure 1.16, pyrolysis occurs when composite waste is
heated to 450
oc- 700 oc in an
inert environment [7, 12, 20, 21]. This inert environment
prevents the oxidation of the fibers (susceptible to induce a reduction of their mechanical
properties), as weil as, the combustion of the resin matrix. The resin is allowed to completely
17
volatilize, thereby producing both liquids and gases composed of lower chained molecules
that can be recovered as chemical feedstock or fuel [20, 22, 23]. The remaining solid is
composed offibers, fillers , char, metal inserts, etc. [7, 12, 20, 21].
Combustible Gases to Heat Reactor
Control led 0 2
environ ment
,
Hot Gases
Scrap
Fee d
So lid Products
(Fibers, Fillers, Char)
____ _
i
Condenser
l
-
"'
---··-·-
1
Liquid
Hydrocarbons
Figure 1.16 A general process flow diagram for pyrolysis processing [20].
High pyrolysis temperatures (700
oc and up) may reduce the sol id matter to char [21].
Consequently, the operating temperature is optimized to ensure the complete degradation of
the resin matrix, while avoiding char formation on the surface of the fibers. The operating
temperature depends primarily on the nature of the resin matrix. Polyester resins can fully
oc, while other resin s, such as epoxies or bismaleimides
(BMI), need temperatures ran gin g from 500 oc to 550 oc [20, 22, 23]
decompose at a temperature of 450
Rather than operating in a completely inert environment, pyrolysis is usually carried
out in a controlled oxygen environment because it offers the advantage of burning char and
other contaminants off the surface of the fibers [12]. As long as the oxygen content is kept to
a minimum, the fibers should not degrade. Furthermore, after pyrolysis, if there is any
remaining char or resin present on the surface of the fibers, a quick oxidation step (increase
ofthe oxygen level within the reactor) can be performed [12].
18
According to Pickering, recycled carbon fi bers reclaimed by pyrolysis processing show
little to no degradati on in their mechanical properties ( < 5 %) [1 7]. However, temperature,
oxygen concentration, and residence time in the reactor can greatly affect their properties. As
mentioned previously, char formation may occur on the surface of the fibers, which would
affect their ability to bond to a new resin matri x [12].
Torres et al. [23] carried out pyro lys is experiments ranging from 300
oc to 700 oc on
Sheet Molding Compounds composed of polyester and glass fibers. Pickerin g carried out
pyrolys is experiments ranging from 350°C to 800
oc
on various composites, including
thermoset and thermo plastic res ins, as we il as glass and carbon fibers [20].
Torres et al. [23] found that there was no signifi cant change in the composition and
gross calorie value (GCV) of the pyrolys is by-prod ucts from 400
oc to 700 oc (Table
1.1 ).
GCV is defined as the energy released as heat when a compound undergoes complete
combustion with oxygen under standard conditions [24]. The gaseo us prod uct was mainly
composed of CO, C02, and C 1_4 hydrocarbons with a GCY of 14 MJ 1 m
3
•
This energy is
sufficient to fuel the reactor which would make the process se lf sustaining. Additi onall y, CO
and C0 2 can be re- introduced into the reactor to prov ide an inert environment. The liquid
product (C 5_20 hydrocarbons) was similar in composition to diesel and had a GCY of 37 MJ 1
kg; therefore, it can be used as e ither chemical feedstock or fuel. Pickering yielded very
similar results. However, he found that epoxy resins produced a gas rich in methane, which
substantially increased the GCV to 43 MJ 1 kg [20].
Table 1.1 Characterization of the liquid and gas pyrolysis products from sheet molding
compounds composed of polyester and glass fi bers [23 , 24].
Pyrolysis Products
Solids
Proportion (wt.%)
70
Liquids:
Aromatics (66 wt.%)
Oxygenated compounds (25 wt.%)
Others (9 wt.%)
[Similar in composition to diesel}
15
Gases:
15
Gross Calorie Value (GCV)
37 MJ/kg
Ethanol: 30 MJ/kg
Diesel: 45 MJ!kg
Gasoline: 58 MJ/kg
Note: Can be used as either
chemical feedstock or fuel.
14 MJ/mJ
~--------
1
1
1
19
Hydrogen: 13 MJ/m J
Natural gas: 43 MJ!m 3
Butane: 133 MJ!m3
Note: Sufficient to fuel
pyrolysis reactor.
CO (60 vol.%)
C02(JO vol.%)
c,_4 (10 vol.%)
1.9.3
The Fluidized Bed Process
For the past 15 years, the University of Nottingham has worked on the deve lopment of
a laboratory scale fluidized bed process, capable of recovering both glass and carbon fibers
from thermoset structural composite waste [ 12, 17, 20, 25]. This process is particularly
suitable for end-of-life components because it can treat heavily contaminated materials. The
fluidized bed process consists of a fast thermal oxidative decomposition of the resin matrix,
which allows for the recovery of fi bers, fillers, metals, etc. [ 12, 17, 20, 26]. As shown in
Figure 1. 17, thi s process requires three main units 1 steps: the fluidized bed reactor, the fiber
and fi lier separation step, and the secondary combustion chamber [26].
Scrap
Feed
Clean Exhaust
~,
Fluidized Bed
1 Reactor
1
Il
_____>
l
Air, Heat
~
Fi bers,
Fill ers &
Vo lati li zed
Polymers
~~~rs & Fi lier lj
Separation
------
----
11
Fibers
Fillers
Vo lat il ized
Polymers
r:-- Secondary
1
Combustion
I
1
~'
Recovered
Energy
Figure 1.17 A general process flow diagram for the fluidized bed process [26].
In the fluidized bed reactor, a stream of hot air with a velocity of 0.4 m 1 s to 1.0 m 1 s
is used to fluidize a bed of silica partie les approximately 0.85 mm in size [20]. The composite
20
waste is fed into the fluidi zed bed. Due to the hi gh operating temperature and the oxidative
atmosphere, the resin volatilizes and partiall y co mbu sts, allowing fo r natu ral segregati on to
occur: heav ier metallic components sink in the bed, w hite fi bers and fi ll ers are carri ed away
by the gas stream [20, 26]. A schemat ic of the fluidi zed bed reactor is shown on Figure 1.18.
The two key parameters affecting the qua li ty of the fi bers are the operating temperature
and the res idence time. The operatin g temperature depends primarily on the nature of the
resin matrix; polyester resins can fully decompose at a temperature of 45 0°C [26], white
oth er res ins, such as epoxies, need hi gher temperatures fro m 500-550°C [1 2, 20). The
residence time mu st be kept to a minimum to avoid severe degradation of the fi bers. This is
achieved by reduc in g the size of the scrap compos ite feed to about 25 mm x 25 mm before
entering the reactor [20, 26).
Clean Flue Gas
Scrap
~~ Recovered
Reactor
312 mm
Silica Bed
312 mm
I SO mm
Cyclone
114 mm
456 mm
1200 mm
Fi bers
Sca ling up the process w ill not significa ntly affect process co nditi ons.
Figure 1.18 A schematic ofthe fluidized bed reactor [17, 25-27).
The gas stream exiting the reactor is a mixture of fibers , fillers and vo latil ized
polymers. Separating the high value recycled carbon fibers from the relative ly low value
fil lers and polymers can be achieved by using a rotating sieve separator and a cyclone. The
rotating sieve separator consists of a rotating mesh that captures long fibers and allows short
fibers and fil lers to pass thro ugh, white a cyclone is used to separate the short fibers from the
fillers. The recyc led carbon fibers are collected and washed in an aqueous solution that may
contai n sizing [26].
21
The volatilized polymers exiting the reactor are not fully combusted. Therefore, to
prevent the release of contaminants in the atmosphere, a secondary combustion chamber
burns the volatilized polymers to produce a clean flue gas. It operates at a temperature of
1000
oc and is capable of recovering approximately 16 MJ 1 kg of energy [26] .
According to Pickering, the fluidized bed process is capable of recovering recycled
carbon fibers with 25 % to 50 % loss in tensile strength and no reduction in ten sile modulus
[17]. Moreover, they have similar surface properties to virgin carbon fibers , and are
completely free of res in and char [25]. They typically have a length comprised between 6 mm
and 10 mm, and are in a ' fluffy ' form.
1.9.4
Catalytic Conversion
Allred et al. [12, 27] and Gosau et a/. [12, 28] have developed a catalytic conversion
process to recycle a wide variety of composites, including both thermoplastic and thermoset
matrices, focusing mainly on aircraft parts and electronic assemblies. This process is capable
of handling a diverse waste stream and does not requires any pre-sorting before treatment.
This tertiary recycling process uses a liquid catalyst to degrade the resin into lower molecular
weight hydrocarbons that can then further reclaimed as fuel or chemicals. After separating
the hydrocarbons, metals, fillers , and fibers can be reclaimed for reuse or disposai. This
process operates at low temperatures and pressures, typically at 150°C 1 150 psi [7, 27, 29].
Figure 1.19 depicts a general process flow diagram for the catalytic conversion process.
22
Cat alyst Fluid &
Hydrocarbon
Product
Scrap
Feed
Solid Produ ct s
(Fibers, Fill ers, M et als)
Figure 1.19 A general process flow d iagram fo r the catalytic conversion process [17].
Accordin g to Pickering, the catalytic convers ion process is capable of recovering high
qua lity recyc led carbon fi bers w ith minimal degradation in tensil e strength ( 1 % to 17 %)
[17]. The recyc led carbon fibers have similar surface properti es to virgin carbon fib ers, and
are compl ete ly free of res in.
The hydrocarbon product leaves the reactor mixed with th e liquid catalyst. A certain
percentage is cyc led back into the reactor, whit e the remainder is separated and recovered
[28]. Shredded compos ite waste fro m damaged FIA-18 horizo ntal stabili zers was recyc led
using the cata lytic conversion process. As shown in Table 1.2, the hydrocarbon product
recovered fro m thi s waste is mostl y composed of pheno lics.
Table 1.2 Chemical composition of hydrocarbon product recovered from catalytic conversion
[29,3 1].
Com pound
Proportion
(wt.%)
Pheno l
67
Gross Calorie Value (GCV)
33
Ethanol: 30 Ml/kg
Toluene
7
Diesel : 45 MJ!kg
t---------------+---------t---M_J_IK__,.~g'----l Gasoline: 58 MJ/kg
Other (Mostly Phenolic derivatives)
MJ/kg
41
26
1.9.5
The Supercritical Fluid Process
23
The supercritical fluid process is a new and promising technology that can convert
polymerie waste back into monomers or petrochemical feedstock [30]. It consists of mixing a
reactive medium with the thermoset structural composite waste, causing the resin matrix to
decompose and dissolve, thereby freeing the fibers. Supercritical fluids possess unique
properties exhibiting both liquid and gas behaviour (low viscosity, high mass transport
coefficient and high diffusivity) [31].
Supercritical alcohols (methanol, ethanol, n-propanol) and acetone have received much
attention as a reactive media since they are readily available, relatively inexpensive and able
to dissolve many organic and inorganic compounds. They also have low critical pressures
cPc) and high critical temperatures (Tc) making them ideal for the breakdown and extraction
oforganic materials. n-propanol (Pc= 5.2 MPa; Tc= 241°C) [31] has a high solubility with
organic materials and is relatively benign, thus making it an ideal candidate [32]. Alkali
catalysts, such as NaOH, KOH, CsOH, may be added to speed up the decomposition rate
[ 17, 31]. A general process flow diagram of the supercritical fluid process is shown on Figure
1.20. This is a solvolytic process; a solvent is used to break up the polymer matrix, thereby
freeing the reinforcing fi bers. The reactor operates at 5 MPa and 31 0-500°C. [31]
Supercritical
Fluid
Fluid &
Hydrocarbon
Product
Scrap
Feed
Solid Products
(Fibers, Fillers, Metals)
Figure 1.20 A general process flo w diagram for the supercritical fluid process [17, 33].
24
Pifîero-Hernanz et al. [33] recycled therm oset structural composites using batch and
semi-continuous supercritical fluid processes. The batch process was found to be ineffi cient,
as it is limited by mass transfer: as th e polymer concentrati on increases in the supercritical
fl uid; its solubility drops until the supercritical fl uid can no longer disso lve the res in matrix.
Therefore, a semi-continuous system is preferred.
Currently, only laboratory scale set-ups have been tested. Larger scale demonstrations
are needed to further assess the viability of using the semi-continuous supercriti cal fluid
process to recover recycled carbon fi bers from thermoset structural compos ites [ 17].
Accordin g to Pickering, the semi-continuous supercritical fluid process is capable of
recovering hi gh quality recyc led carbon fi bers with little to no reduction in tensile properti es
(< 3 %) [1 7, 32]. Furthermore, th e surface of the fi bers is clean and exhibi ts good bonding
with epoxy resin.
The supercritical fluid process decomposes epoxy res111 into phenolic based
compounds as shown in Table 1.3 [ 17].
Table 1.3 Chemical composition of decomposed polymers produced by the semi-conti nuous
supercritical fluid process [17].
1.9.6
Chemical Species
Corn position (wt. % )
Phenol
p-isopropylphenol
p-isopropenylphenol
m-methylphenol
m-ethylphenol
Other
34.9
26.4
18. 1
6.5
4.7
9.4
Other Available Technologies
Various other technologies have been studied to recycle thermoset structural
composites. However, they proved to be unsuccessful or difficult to scale-up. Microwave
treatment, for example, is capable of recovering high quality recycled carbon fibers from
thermoset structural composites but its scalability is an obvious issue [34]. Examples of
25
unsuccessful treatment methods include chemical treatment, molten salt treatment, and
thermal shock treatment [35, 36].
1.10
Re-manufacturing Carbon Fi ber Reinforced Thermoset Composites
1.10.1
Overview
Recycled carbon fibers recovered by any of the above mentioned methods are in
chopped form ; therefore, they will have to be used as discontinuou s reinforcement in new
composite materials [12, 17]. However, reintegrating chopped recycled carbon fibers in new
resin matrices poses severa! challenges, as most manufacturing processes are designed for dry
reinforcements available as continuous fibers or woven fabrics.
There are severa! options for producing thermoset composites containing chopped
recycled carbon fibers [6, 7, 12]. The following techniques will be will be discussed in detail
later on in this chapter. Recycled carbon fiber mats can be fabricated by either a wet-lay
process [37] or by carding, and then impregnated with a resin system by either wet lay-up, or
by liquid molding processes, which includes resi n transfer molding (RTM) or infusion 1
compression molding. Another option would be to use sheet molding compound (SMC),
where chopped recycled carbon fibers and resin paste in B-stage are mixed beforehand, and
then undergo compression molding to form the final composite piece. Finally, thermoplastics
can also be produced by mixing recycled carbon fibers and thermoplastic resin in an extruder,
producing pellets that can then be re-melted and shaped into a composite piece by injection
molding. This discussion will be limited to re-manufacturing carbon fiber reinforced
thermoset composites.
1.1 0.2 Fabricating Recycled Carbon fi ber Mats
Recycled carbon fi ber mats can be produced by either a wet lay process (Figure 1.21)
or by carding. The wet-lay process [37] is commonly used for making paper, and is weil
suited for making recycled carbon fiber mats. The fibers are agitated and dispersed in the
mixing tank. The mixture is then pumped into the headbox, where a vacuum sucks the fibers
onto an inclined conveyor screen (form ing wire), whi le simultaneously removing excess
26
water. Finally, the fibers in the resulting mats are binded together and dri ed in an oven.
Generally, fibers lay randoml y onto the screen, however, they can be preferent ia lly oriented
in the direction of th e trave lling conveyor screen by increas in g the be lt speed.
11indcr
Mixi n ~
/
Ta nk
-
A!!i tator
Head Box
1
____. Arrlicator § vne
--··-··-0-.. ··-·· - 0
~ Takc up
Ro ll
Figure 1.21 Wetlay Process for making recyc led carbon fi ber mats [39].
Carding is a mechani cal process that disentangles, cleans and intermi xes fi bers to
produce a cont inuous web suitable for yarn production. Genera lly, thi s process is used fo r
natural fi bers such as cotton or wool. In thi s work, a roto-carder (F igure 1.22) produced
recyc led carbon fi ber mats by separating, interl ocking and partly ali gnin g recyc led carbon
fi bers.
Figure 1.22 Carding process for making recycled carbon fi bers mats
1.10.3 Wet lay-up processing
27
As depicted in Figure 1.23, wet lay-up processing consists of laying a recycled carbon
fiber mat into a mold, and saturating it with liquid resin . Rollers can then be used to spread
the res in uniformly into the mat, th us reducing the void volume. Additional layers of mat and
resin can be laid onto one another until the required composite thickness is reached. The
assembly is finally cured at room temperature or in an oven. This is a very simple method to
produce recycled carbon fiber reinforced thermoset composites; however, it is generally very
difficult to control the uniformity ofthe piece, as there is little control on the resin content.
Dry Rein fo rcement
Fabric ~
Optional
Gel Coat
Consolidation
Raller
Mould Tool
Figure 1.23 A schematic representation of the wet-lay process [6] .
1.10.4 Resi n Transfer Molding
Resin transfer molding (RTM) is schemati cally depicted in Figure 1.24 . Recycled
carbon fiber mats are stacked up and compacted into a mold . The mold is then pre-heated to
the cure temperature, and the mats are subsequently impregnated by injecting resin at high
pressures at the inlet position. At the outlet position, vacuum can be app lied to help the resin
to flow into the mat. Once fully impregnated, the resin is cured. RTM allows the fabrication
of composite parts with high fiber volume fraction (up to 60 wt. %), consistent quality, and
law void volumes. However, if the permeability of the mats is too low, RTM cannot be used
as the required injection pressures become tao high .
28
Press or clamps to hold
ha Ives of tool together.
Mould Tool
~
Res in
lnjected
Under
Pressure
Optional
Vacuum
Assistance
Mould Tool
Dry Reinforcemenl Preform
Figure 1.24 A schematic representation of Res in Transfer Molding (RTM) [6].
1.1 0.5 Infusion Molding
A schematic of the infusion process is given in Figure 1.25. The system consists of a
mold tool on the bottom, the recycled carbon fiber mats in between, and a flexible membrane
(vacuum bag) on top . The resin is infused into the mats by applying vacuum to the system.
Once fully impregnated, the resin is either cured in an oven or undergoes compression
molding for further compaction. fnfusion molding allows for the fabrication of composite
parts with fiber volume fraction up to 55 wt. %, if adequate compaction is achieved . This
process is less expensive than RTM, and provides better quality parts than the wet lay-up
process. However, controlling the resin uniformity can be difficult, leading to resin rich areas
in the corners or at the edges of the final composite piece.
Sealant Tape
Resin drawn across and through
rein forcements by vacuum
Vacuum Bag
Res in
Peel Ply and/or Resin
Distribution Fabric
)
Mould Tool
To Vacuum
Pump
'---- -
29
Figure 1.25 A schematic representation of infusion molding [6].
1.10.6 Sheet Molding Compound (SMC)
A schematic of the SMC process and compression molding is given in Figure 1.26 and
Figure 1.27. SMC sheets are a semi-finished product made from chopped recycled carbon
fibers and resin paste in B-stage (B-stage is an intermediate stage in a thermosetting resin
reaction in which the polymer softens but does not fuse when heated, and swells but does not
dissolve in contact with certain liquids). They are obtai ned by passing chopped recycled
carbon fibers and resin through compaction rollers forming a sheet. The resulting SMC sheets
are the placed into a mold, and compression molded . The SMC process can be highly
automated to increase production rate. Moreover, it allows for the production of composite
parts with fiber volume fractions up to 55-60 wt. %, and low void volumes. However,
formulation and compounding of the SMC sheets from the raw materials (fi bers and res in) is
challenging.
Figure 1.26 Schematic representation of the SMC process [7].
30
Heat and Pressure
Female Mold
Half
Composite
Charge
Heat and Pressure
Male Mold
Hait
Figure 1.27 Schematic Representation of Compression Molding [7].
1.11
Summary
The economie viability of recycling carbon fiber reinforced thermoset composite waste
depends on the ability of recovering high quality recycled carbon fibers . Thermoset
composites can then be re-manufactured using these recycled carbon fibers. In thi s work,
recyc led carbon fibers were recovered from thermoset composite waste generated by the
Canadian aerospace industry, using Materials Innovation Technologies commercial scale
pyrolysis process. In this work, recycled carbon fibers were recovered from thermoset
composite waste generated by the Canadian aerospace industry, using Materials Innovation
Technologies commercial scale pyrolysis process. In this work, recycled carbon fibers were
recovered from thermoset composite waste generated by the Canadian aerospace industry,
using Materials Innovation Technologies commercial scale pyrolys is process. Chapter II
assesses the effect of pyrolysis processing on the morphological, mechanical and surface
properties of the recycled fibers by evaluating and comparing them to a virgin fiber reference.
The properties of the recycled fi bers were found to be suitable for composite consolidation,
and th us, Chapter III covers the fabrication of epoxy 1 recycled carbon fi ber plates, as weil as,
an evaluation of their morphology and mechanical properties. The recycled fi ber composites
were found to have excellent mechanical properties when compared to pure epoxy, and
comparable properties to a virgin equivalent. Therefore, the potential of reintegrating
recycled carbon fibers as reinforcement in new thermoset composites for a variety of
applications has been demonstrated.
CHAPITRE II
EFFECT OF MORPHOLOGICAL, MECHANI CAL AND SURFACE PROPERTIES ON
THE WETT ABILITY AND INTERF AClAL ADH ESION OF RECYCLED CARBON
FlBERS*
Stefan Andjelic 1, Loleï Khoun 2',
1
athalie Legros2 ' , Steen Brian Schougaard 1'
Chemistry Department, Un iversité du Québec à Montréal
2 101 Rue Jeanne-Mance, Montreal, H2X 216, Quebec, Canada
2
Natio nal Research Council Canada
75 boulevard de Mortagne, Boucherville, J4B 6Y 4, Quebec, Canada.
* Correspond ing authors:
Lolei Khoun
e-mai l: [email protected]
Telephone: (00 1) 450-64 1-5435
Fax: (00 1) 450-641 -5105
Nathalie Legros
e-mail: Nathali e.Legros@i mi.cnrc-nrc.gc.ca
Telephone: (00 1) 450-64 1-5866
Fax: (001) 450-641-5105
Steen Brian Schougaard
e-mail : [email protected]
Telephone: (001) 514-987-3000 ext. 3911
32
Fax: (001) 514-987-4054
* This article is intended for publication in the Journal of Material Science.
2 .1
Abstract
Chopped recycled carbon fibers from prepreg and tooling were recovered from carbon
fi ber reinforced thermoset composite waste generated by the Canadian aircraft industry, using
Materials Innovation Technologies commercial scale pyrolysis process. The objective was to
analyze the effect of pyrolysis processing on the morphological, mechanical, and surface
properties of recycled carbon fibers, and to determine how their synergistic interactions
affected wetting and interfacial adhesion with epoxy resin. Recycled carbon fibers were
characterized by: scanning electron microscopy, den sity measurements by pycnometry,
micro-tensile testing, BET analysis, x-ray photoelectron spectroscopy, wettability analysis by
dynamic contact angle measurement and interfacial adhesion with epoxy resin by microdroplet testing. The results indicate that pyrolysis processing altered the surface properties of
the recycled carbon fibers by effectively removing sizing and resin , thereby revealing surface
topographies. Wetting and interfacial adhesion between the surface of recycled carbon fibers
and epoxy resin were found to be predominantly affected by Lewis acid 1 base interactions of
oxygenated surface functional groups, as weil as, by mechanical interlocking. Mechanical
interlocking appeared to be the more important parameter, as the striated prepreg fibers outperformed the smooth tooling fibers in micro-droplet testing regardless of the chemical
surface properties.
33
2.2
Introduction
The use of carbon fiber reinforced thermoset composites has doubled in the last
decade, generating a significant amount of waste, estimated at 3,000 ton s per year in North
America and Europe [ 1]. As a result, major users like aircraft manufacturers are un der
pressure to reduce waste through recycling or reuse, affectin g both in-process waste and endof-life disposai. Fiber reclamation has gained momentum because of its ability to recover
high quality carbon fibers by employing either a thermal or chemical process to break down
thermosetting resin [2, 3]. The most common fiber reclamation method is pyrolysis
processing [2-4] , defined as the thermal degradation of organic material in a controlled
oxygen environment. Other fiber reclamation technologies include catalytic conversion [3 , 5,
6], fluidized bed reactor [2, 3, 7, 8] and supercritical fluids [9, 10] .
Recycled carbon fibers have already been reintegrated as reinforcing fibers in new
polymer composites [2, 3, 11-13] , however, further optimization of their mechanical
performance requires better knowled ge of the fiber 1 resin interface. Interfac ia l properties can
be characterized by wettability and interfacial adhesion. Complete wetting is a prerequisite
for good adhesion because it prevents the formation of voids; while, good adhesion is
essential for stress transfer between fiber and resin, as it is weil correlated with the
interlaminar shear strength (ILSS) of composite materials [ 14-16].
Severa! studies [2, 3, 17-19] have reported that recycled carbon fibers retained their
morphological and mechanical properties, however, pyrolysis processing altered their surface
properties by removing resin and sizing, and altering the distribution of oxygenated surface
functional groups. These functional groups play an important ro le in wetting and interfacial
adhesion, as they interact through Lewis acid 1 base interactions with epoxy resin [14, 15].
Y et, the Lewis acid 1 base surface characteristic of recycled carbon fibers has not been
thoroughly investigated.
In this study, chopped recycled carbon fibers were recovered from carbon fiber
reinforced thermoset composite waste generated by the Canadian aircraft industry, using
Materials Innovation Technologies commercial scale pyrolysis process. The objective was to
34
analyze the effect of pyro lys is processing on the morphological, mechanical, and surface
properties of recycled carbon fibers, and to determin e how their synergisti c interactions
affected wetting and interfac ial adh es ion with epoxy resin . Morphology was probed by
Scanning electron microscopy, whil e their mechani cal performance were assessed by mi crotensile testing. Surface properties were probed by BET analys is, x-ray photoelectron
spectroscopy, wettability study by dy nami c contact angle analys is, and interfac ial adhes ion
by micro-drop let testing with epoxy res in .
2.3
Materials
2.3 .1
Carbon Fibers
Recycled carbon fi bers were recovered from a 100 kg sample of carbon fi ber
reinfo rced thermoset co mposite waste generously donated by Bell Heli copter Textron Canada
Ltd. (BHTCL: Mirabel, Quebec, Canada). Thi s sampl e was composed of actual waste
generated by the Canadi an aerospace industry . Tt co ntained carbon fi ber prepregs (cured and
uncured) based on epoxy and bismaleimide resins, and tooling parts made fro m carbon fibe r
reinforced epoxy resin with trace amounts of silicone. Pyrolysis processi ng was performed at
Materials Innovation Technologies (MIT: Lake City, South Carolina, United States) using
their commercial scale batch pyrolys is oven. Before pyrolys is, the waste was sorted and eut
into 2.5 cm x 2.5 cm fragments to limit the fiber length di stributi on, thereby controlling the
overall uni form ity ofth e recycled fi bers. Pyro lys is was perfo rmed at low temperatures(< 400
°C) under a contro lled atmosphere, and the res idence time was adju sted as a function of th e
material to be pyro lyzed. Recycled carbon fi bers were obtained fro m prepregs and tooling.
As the recyc led fi bers origi nate from differe nt feedstock, they are composed of var ious types
of carbon fi bers. Hence, it was not poss ible to preci se ly evaluate the effect of recyc li ng on
their properties. Therefore, th e performance of the recycled fibers was compared to Torayca@
T700S (Toray fi bers: sized, tensile modulus: 230 GPa, tensile strength: 4,900 MPa),
aerospace grade virgin carbon fibers from Toray (Fiower Mound, TX, USA). For BET
analysis, Panex® 35 (Panex fibers: unsized, chopped to a length of 6 mm), ind ustrial grade
virgin carbon fi bers fro m Zoltec (St. Louis, MO, USA) were selected, as they had an unsized
surface. Upon visual inspection, the recyc led fi bers fro m prepreg had a woven structure and
were eut into squares, while the recycled fibers from tooling were in a "fluffy" entangled
- - - - - - - - - - - - -- --
- - -- - - - - - - - - - - - - - - - - -- - - - - -
35
state . The Toray fibers , on the other hand, were spooled as a tow and subsequently eut into
2.5 cm lengths.
2.3.2
Resin
PRISM™ EP2400, an infusion grade epoxy system produced by Cytec Engineered
Materials (Woodland Park, NJ, USA), was selected as the polymerie matrix for micro-droplet
testing (Table 2.1 ).
Table 2.1 Processing properties of the infusion grade epoxy PRJSM™ EP2400 produced by
Cytec Engineered Materials.
Properties
Injectable Temperature ( 0 C)
Cure Temperature ( 0 C)
Dry Tg (room temperature, dry)
Wet Tg (48 hour water boil, wet)
Toughness
Cured Resin Density (g/cm 3)
2.4
Experimental
2.4.1
Characterization of Carbon Fi ber Morphology
PRISM EP ™2400
70
180
179
163
Very High
1.24
Scanning Electron Microscopy
Fiber morphology was probed by a Jeol GSM 840 scannmg electron microscope
(SEM) operating at 5 kV. Fiber diameters were measured using lmageJ software [20].
Reported values are the average of 5 samples for each fi ber type.
Fiber Density Measurement
The recycled fiber density was measured with an InstruQuest Humipyc gas pycnometer
(gas: helium, measurement pressure: 210 kPa ± 3 Pa, stabi li zation ti me: 300 s, temperature:
21.5 oC, relative humidity: 17 %). Reported values are the average of 3 measurements.
,-~~~ -~~-
· ~~~~
36
2.4.2
Characterization of Carbon Fi ber Mechanical Properties
Micro- Tensile Tes ting
Micro-tensile testing was performed on mono-filaments according to ASTM 03379
[21] using an lnstron M icrotester eq u ipped with a 2N load ce li. A gage length of 10 mm and
rate of 1 mm 1 min were used. Reported values are the average of 30 samples for each fi ber
type. In ali cases, error bounds represent the 95 % confidence limits for a student-t
distribution.
2.4.3
Characterization of Carbon Fi ber Surface Properties
BET
Carbon fi bers were analyzed by adsorption isotherms of N 2 at 77 K. Quantachrome
Instruments (Boynton Beach, FL, USA) Autosorb 1- MP equipment and software performed
20 point adsorption 1 20 point desorption isotherms, 7 point BET for specifie surface area
determination, and pore size distribution analysis. Pore size was characterized according to
IUPAC [22] as follows: micro-pores (< 20 Â), meso-pores ( > 20 A and < 500 Â), and
macro-pores ( > 500 Â).
X-Ray Photoelectron Spectroscopy
X-Ray Photoelectron Spectroscopy (XPS) analysis was performed using a Physical
Electronics PHJ 6500-ci with a Al standard anode (1486.6 eV) at 200 W for the survey
spectra, and a Mg Ka (1253.6 eV) at 150 W for the high resolution spectra. No charge
compensation was required. Ali spectra were recorded at a 45° take-off angle, and the area
under analysis was 800 x 200 Jlm for ali scans. The spectra were analyzed by CasaXPS
software using an internai reference of284.6 eV for the C 1s peak. Survey scans determined
the surface elemental compositions, wh ile the C 1s high resolution scans determined the
concentration of oxygenated surface functional groups. The curve fittin g procedure was
described by Jiang et al. [7, 23].
Wettability study by Dynamic Contact Angle Analysis
A Dataphysics DCAT 11 Dynamic Contact Angle Meter and Tensiometer employing
the Wilhelmy plate technique was used to measure contact angles using appropriate liquid
37
probes, which then characterize the Lifshitz - Van der Waal and Lewis acid 1 base
contributions to the surface free energy of the carbon fibers [24]. Mass deflection was
measured as the probe liquid was raised and lowered, measuring both the wetting and tear-off
force according to the following relationship [15 , 25]:
mg
cose = Pyl
where
e is
(2. 1)
the contact ang le, m (g) is the mass deflection, g is the gravitational
constant (9.81 m 1 s\ Pis the wetted fiber perimeter and y 1 (mN 1 m) is the surface tension
ofthe probe liquid .
Samples were prepared by gluing carbon fibers to a paper template that was suspended
from a microbalance by a hook. Probing liquid was placed into a beaker that was held in
place by a micrometer stage. The suspended sample was brought into contact with the liquid
surface and subjected to one cycle of immersion at a speed of 100 )..un 1 s and a depth of 3
mm . Mass deflection data were recorded at 5 Hz with a mass resolution of± 10 ).!g. n-hexane
was used to determine the average fiber perimeter, while 1-bromonaphthalene, water, and
glycerol were used to characterize the surface free energy of the fi bers. Reported values are
based on 20 observations for each fi ber type (5 replicates for each liquid probe).
Micro-droplet Testing
Micro-droplet testing [7, 23 , 26] quantifies the interfacial shear strength ('r), i.e. the
adhesion between the fiber and epoxy matrix. A normal force was applied on a micro-droplet
ofresin using shearing blades that pull the resin off the fiber. Assuming a cylindrical model,
the interfacial shear strength was calcu lated by:
r = F /rrD1 L
(2.2)
where F is the debonding force, Dr is the fi ber diameter, and L is the embedded length.
38
Samples were prepared by gluing the end s of a carbon mono-fi lament onto a 4 cm x 1
cm paper template w ith a punch ho le through the middl e. E lliptical epoxy droplets were
a pplied onto the monofi lament using a fin e metal applicator co nnected to a heated so ld erin g
iron. Sam ples were cured in an oven fo r 2 hours at 180 °C. Droplets with embedded lengths
varyi ng between 20
)..lill
to 50 J..Lm were chosen for testing. Observations were made usi ng a
N ikon Ecl ipse SOi optical mi croscope con nected to a Qlmagin g Go-3 camera, and
measurements were made using ImageJ software calibrated with a Pyser-SG I S8 stage
micrometer graticul e. A caliper attached to a Mi cos MT-65 linear stage served as shearin g
blades. The caliper opening was set to 10
)..lill
an d the speed was set to 0.1 mm 1 min. Force
meas urements were acquired using a Mettl er To ll edo AB 135 -s/FACT ba lance connected to a
computer using Nati onal Instruments LabV iew software. Reported values are based on 15
observations fo r each fi ber type .
2.5
Results and Discuss ion
2 .5. 1
Characterisation of Carbon F iber Morph ology
SEM micrographs (Figure 2. 1) revea led that the recyc led fi bers from prepreg and
too ling were re lati ve ly un damaged, havi ng no obvio us cracks. Their di ameters measured 6.5
± 0.8 J..Lm and 6.5 ± 0.9 J..Lm respective ly. Pre preg fi bers exhibited surface striations des igned
to improve their adhes ion with epoxy [7, 23 ], and res idual res in was ofte n observed, probably
due to a lack of optimi zation of the pyro lys is process (the process was optimi zed fo r epoxy
compos ites, w hereas prepreg waste contai ned both epoxy and bismalei mide res ins). Too lin g
fi bers showed sorne loose debris and no surface striations. The Toray fi bers, on the other
hand, have a coating of sizing clearly visib le on their surface, which is designed to improve
adhesion with epoxy res in and protect the fi bers against abrasion [ 14]. The average density of
3
the prepreg fibers was determined by pycnometry to be 1.75 g 1 cm , close to the val ue of the
Toray fibers (1.80 g 1 cm
3
).
Overall, the recycled fibers retained their bu lk morphological
properties summarized in Table 2; however, pyro lysis process ing altered surface texture and
chemistry by removing resin and sizing, thereby revealing their surface topographies.
39
a)
b)
c)
Figure 2.1 SEM micrographs ofthe recycled carbon fibers from a) prepregs, b) tooling, and
virgin carbon fibers from c) Torayca@ T700S.
40
Table 2.2 Summary of carbon fiber morphology.
Carbon Fiber Type
Diameter (J.lm)
6.5 ± 0.8
Recycled Fibers from Prepreg
6.5 ± 0.9
Recycled Fibers fromTooling
6.5 ± 0.6
Torayca® T700S
* Torayca@T700S Datasheet
2.5.2
Density
3
(g 1 cm )
1.75
1.80*
Surface Striations
Sizing
yes
no
*
no
no
yes*
Characterization of Carbon Fiber Mechanical prope1ties
Micro-tensile testing was performed to determine the effect of pyrolysis processing on
the mechanical performance of the recycled fibers. The recycled fibers from prepreg and
tooling had a tensile modulus of 160 ± 20 GPa and 170 ± 10 GPa, and a maximum tensile
strength of3400 ± 400 MPa and 3800 ± 200 MPa, respectively (Figure 2.2). When compared
to the Toray fi bers, average differences of -10 % to - 5 % in ten sile modulus and - 20 % to 10 % in maximum tensile strength were observed. Tooling fi bers offered a better mechanical
performance than prepreg fibers , although prepreg composites contain hi gh performance
aerospace grades of carbon fibers, while tooling composites generally contain industrial
grades of carbon fibers. This result may be due to process variations that can occur during
recycling (possible degradation of the fiber surface). Therefore, further optimization of the
pyrolysis conditions (temperature, residence time, and atmosphere), with respect to the type
of composite waste being treated , should contribute to further improving the mechanical
properties of the fi bers. Overall, the recycled fi bers retained the ir mechanical properties.
41
•Tensi le Modulus
~
<0
DT ensile Strength
200
5000
180
4500
160
4000
140
3500
120
3000
&.
Q. 100
2500 ~
w
80
2000
60
1500
40
1000
20
500
K
0
e
b
0
Prepregs
Tooling
Toray
Figure 2.2 Tensile modulus E (GPa) and max imum tensil e strength Œmax (MPa) of the carbon
fi bers.
2 .5.3
Characterizati on of Carbon Fiber Surface Chemi stry
Figure 2.3 di splays the N 2 adso rpti on and desorption isotherm s fo r the recyc led fibers
from prepreg and too ling. Both isoth erm s were of type II nature, indicating that th e recyc led
fibers were non-poro us so lids [27]. In additi on, very little hysteres is was observed between
th e adsorption and desorption isotherm s, signify ing that th ere were no large meso- or macropores (i.e. large cav it ies) present on their surface [27].
The recycled fibers were in itially compared to the sized Toray fibers for BET analysis.
However, sizing is a po lymerie coati ng that can cover up surface defects, making it difficult
to evaluate the effect of pyro lys is processi ng. Therefore, unsized Pan ex fi bers were offered as
a more appropriate comparison. 7 point BET analysis (Tab le 2.3) determined that the
recyc led fi bers had a specifie surface area approxi mately 9 times greater than the Toray
fibers, and 43 times greater than the Panex fibers. Moreover, pore size distribution plots
(Figure 2.4) established that this substantial increase was due to the introduction of many
small pores ( < 100 A) on the surface of the recycled fi bers. The presence of meso-pores on
the Toray fibers was attributed to the uneven coating of sizing, wh ile for the Panex fiber; it
,-----~ ------------ ---- -
----·
--
--
42
was attributed to surface defects. Generally, an increase in the specifie surface area of carbon
fibers should improve interfacial adhesion between fiber and resin, as there is more intimate
contact at the interface [ 15]. However, epoxy res in cannat penetrate su ch small pores [15],
and subsequent micro-droplet testing shows thi s, as adhesion between the recycled and Toray
fibers were quite similar. Therefore, BET analysis revealed that pyrolysis processing
effectively removed sizing and res in, and slightly degraded the surface of the recycled fi bers
by the introduction of small pores, which had little effect on their interfacial properties with
epoxy resm .
Table 2.3 Specifie surface area (m 2/g) of the carbon fibers.
Fiber Type
Recycled Fibers from Prepreg
Recycled Fibers from Tooling
Torayca@T700S
Panex® 35
Specifie Surface Area (m 2/g)
43
43
5
1
- -- -- - -- - - - - -- -- - - -- -- -- - - - - -- -- -- - - - - - - - - ,
43
a)
25
20
êi
1 15
~
Q)
E
2 10
0
>
- -- - Adsorption
5
-- -- - Desorption
0
0
0.2
0.4
0.6
0.8
P/P 0
b)
25
20
êi
1:
15
~
Q)
5 10
0
>
- -- - Adsorption
5
- -- - - Desorption
0
0
0.2
0.4
0.6
0.8
P/P 0
Figure 2.3 20 point N 2 adsorption 1desorption isotherms. Vo lume ( cm3/g) versus relative
pressure P/P 0 for the the recyc led fi bers from a) prepreg and b) Tooling.
44
a)
b)
2.00E-03
2 OOE-03
1.50E-03
1.50E-03
1.00E-03
1.00E-03
S.OOE-04
5 OOE-04
,-...
OJ)
.......
..,~
s
.._.,
<:)
Q)
s
=
0
>
Q)
1.
0
~
O.OOE+OO
0
1~
100
0 OOE+OO
200
300
0
400
c)
~
100
200
100
200
300
400
d)
2.00E-03
2.00E-03
1.50E-03
1.50E-03
1.00E-03
1.00E-03
S.OOE-04
S.OOE-04
]
.....
=
Q)
1.
~
.....
~
~
O.OOE+OO
O.OOE+OO
0
100
200
300
400
0
300
400
Pore Width (Â)
Figure 2.4 Differentiai pore vo lume (cm 3/Â/g) vers us pore widths (À) for the recyc led fibers
from a) prepregs, b) Tooling, and virgin fi bers from c) Torayca@T700S and d) Pan ex®3 5.
The surface chemistry of the carbon fi bers was probed by XPS. Survey scans (Figure
2.5) showed carbon at a binding energy of 284.6 eV, followed by oxygen (532 eV), nitrogen
(399 eV) and silicon (101 eV). Trace amounts of sodium (1070 eV), calcium (346 eV) and
chlorine (198 eV) were also detected, and were most likely contaminants from the carbon
fiber manufacturing process [7, 23].
Based on the survey scans, Table 2.4 displays the elemental composition on the surface
ofthe carbon fibers. The oxygen to carbon ratio (0 1 C) is the most important parameter, as it
45
determines the concentration of oxygenated surface functional groups, which serve to
improve wetting and interfacial adhesion with sizing and resin [14, 15]. However, a high 0 1
C ratio (i.e. severe oxidation) forms fissures, causing a weak boundary layer that is
detrimental to both interfacial adhesion, and the inherent mechanical properties of the fibers
[ 15]. Epoxy sizing on the Toray fi bers had a 0 1 C ratio of 0.22 [7], wh ile the 0 1 C ratio for
the recycled fibers from prepreg and tooling were 0.46 and 0.15 respectively. Pyrolysis
processing heavily oxidized the surface of the prepreg fibers, which explains why it did not
perform as weil as the tooling fibers in micro-tensile testing. The Nitrogen content varied
from 2 - 3 %, and was attributed to nitrogen containing functional groups present in PAN
based precursors used during carbon fiber manufacturing, sizing, and resid ual resin. Tooling
fibers were known to be contaminated with silicon; however, ali the fibers contained
significant amounts of it, suggesting that it mu st have been incorporated in sizing or res in.
In order to quantify the concentration of oxygenated surface functional groups, C 1s
high resolution spectra (Figure 2.5) were curve fitted by 6 components according to a
procedure described by Jiang et al. [7, 23): a graphitic (C-C) peak at 284.6 eV, hydroxyl (COH) peak at 286.1 eV, carbonyl (C=O) peak at 287.6 eV, carboxyl (COOH) peak at 289.1
2
-)
eV, carbonate ion (C0 3
peak at 290.6 eV and n-n* transitions peak at 291.5 eV. The results
are displayed in Table 2.5. The proportion of oxygenated surface functional groups did not
change significantly; however, there was sorne evidence of surface oxidation by pyrolysis
processing, as hydroxy l groups on the recycled fibers oxidized into higher oxidation state
carbonyl groups. Both the recycled and Toray fibers showed evidence of carboxyl groups,
making them favorable for wetting and adhesion with epoxy resin [28].
46
Table 2.4 The surface elemental compositions(%) based on the XPS survey scans ofthe
carbon fibers.
Fiber Type
C ls
285 eV
0 ls
532 eV
N ls
399 eV
101 eV
Torayca@ T700S
Prepregs
Tooling
75 .64
57.14
82.56
16.51
26.45
12.44
2.48
3.37
2.81
5. 15
12.65
1.87
Si2p
Na l s
1070 eV
Ca 2p
346 eV
0.14
0.09
Cl 2p
198 eV
0.17
0.14
0 /C
0.22
0.46
0.15
Table 2.5 Curve fitting results for the C 1s hi gh resolution scans of the carbon fibers.!!. is the
variation expressed in(%) with respect to Torayca® T700S virgin carbon fibers.
C-OH
C-C
Fi ber Type
284.6
il.
eV
Toraycailll
T700S
Prepregs
Tooling
19.82
20.20
il.
cV
24 .24
1.89
-2.06
287.6
6.6 1
10.47
289.1
il.
eV
2.87
-4.42
-4 .04
co,.
COO H
C-0
il.
eV
6 1.84
63 .73
59.78
286. 1
6.78
9.51
7t-7t*
il.
eV
8.85
3.74
7.6
290.6
0.83
0.00
il.
eV
0.00
-2.07
0.66
291.5
2.20
0.83
0
2.22
0.04
0.02
-2. 16
47
High Resol utio n Scans
Sur·vey Scans
a)
6000
4000
2000
0
0 200 400 600 800 100012001400
+------~---~-----1
280
285
290
295
b)
30000
6000
20000
4000
10000
2000
0
200 400 600 800 100012001400
+----~---~-----1
280
285
290
295
c)
30000
6000
20000
4000
10000
2000
0
200 400 600 800 100012001400
+----~---~------1
280
285
290
295
Binding Energy (eV)
Figure 2.5 XPS survey and high resolution C 1s spectra for the recycled carbon fi bers from
a) prepreg, b) tooling, and virgin carbon fi bers from c) Torayca® T700S .
48
Dynamic contact angle analysis (DCAA) probed the effect of pyro lysis processing on
the wettability of the fi bers by measuring the ir surface free energy at the macroscopic scale.
According to the Van Oss-Chaudhury-Good method [14, 24], which uti lizes contact angles,
measured using liquid probes, the solid surface free energy term, Ys is related to contact
angles as follows:
(2 .3)
(2 . 4)
(2.5)
where yfw and yfw are the Lifshitz - Van der Waal components, Ys+ and Yt are the
electron acceptor components (i.e. lewis acid), and Ys- and y1- are the electron donor
components (i.e. lewis base) for the so lid and liquid surfaces respectively. YsAB is the the
lewi s acid 1 base contribution of the so lid surface, and is equal to the geometrie mean
between
y/ and Ys-.
A system of3 independent equations is required so lve the 3 unknowns (YsLw , Ys+, Ys-)·
Table 2.6 lists the 4 probe 1iquids that were used. n-hexane was used to determine the average
fi ber perimeter as it efficiently wets the surface (assume 8
=
0 in equation 1). 1-
bromonaphthalene is a non-polar liquid and is used to measure the Lifshitz - Van der Waal
component, while water and glycerol are polar liquids and are used to measure the lewis acid
1 base components.
Table 2.6 Surface free energy components (mN 1 rn) of the probing liquids.
Liquid Probes
n-hexane [29]
1-bromonaphthalene [30]
Water [15]
Glycerol [14]
Yt
yLW
y[
Yi
18.49
44.4
72.8
64
18.49
44.4
21.8
34
25.5
3.92
25.5
57.4
l
As shown in Table 2.7, the recycled fibers from prepreg and tooling had a surface free
energy of 46±3 mN 1 rn and 55 .6±0.2 mN 1 rn respective ly, while the Toray fibers was
· - - - - - - -- -- -- - - - - - - - - - - - - - - -- -- - - - - -- -- - - - - - - - - - - - - - - -- - ,
49
slightly lower at 45± 1 mN 1 rn because sizing covers up high energy sites [28]. The Lewis
acid 1 base contribution compared to the total surface free energy of the fibers was
significant, varying between 39 % to 54 % for the recyc led fibers and 44 % for the Toray
fibers . The Lewis acid 1 base contribution was attributed to the hydroxyl, carbonyl, carboxyl
and carbonate oxygenated surface functional groups seen on the XPS C 1s high resolution
scans, as they show strong Lewis ac id 1 base behavior compared to grap hene [ 14, 15]. Lew is
acid 1 base interactions play an important ro le in carbon fiber 1 epoxy adhesion, as most
notab ly, carboxyl groups can covalently bond with epoxy groups [28].
The surface of al i fi bers had an electron donor nature (Ys-
> Ys+).
For the Toray fi bers,
the electron donor nature of the surface was attributed to epoxy based sizing [14], wh ile for
the recyc led fibers , it was attributed to the oxygenated surface functiona l groups and
impurities . Pyrolysis processing altered the e lectron acceptor 1 donor balance, as hydroxy l
groups oxidized into higher oxidation state carbonyl groups. Moreover, positively charged
ions (Na+, Ca2+), as weil as, residual resin and contaminants, also influenced the electron
acceptor 1 donor nature of the oxygenated surface functional groups. Overal l, the recyc led
fibers had high surface free energies with significant Lewis ac id 1 base contributions, making
them favorable for epoxy wetting and ad hesion.
Table 2.7 Surface free energy components (mN 1 m) of the carbon fibers .
Carbon Fiber Type
Torayca@T700S
Prepregs
Tooling
Ys
y~W
r:B
Yi
y;
Y: 8 fYs
45± 1
46±3
55 .6±0.2
25±3
28±4
25±3
20±3
18±4
30±3
4±2
3±2
8± 1
24±5
24±8
27±2
0.44
0.39
0.54
Interfacial shear strength plays a critical ro le in stress transfer between fiber and resin
in composite materials; additionally, it is a quantitative measure of interfac ia l adhesion [7,
14, 15, 23, 3 1]. M icro-drop let testing determined the interfacia l shear strength of the carbon
fibers with epoxy resin, and the results are di splayed in Table 2.8. When compared to the
Toray fibers, no difference was observed in the interfacial shear strength of the prepreg
fi bers, wh ile, on average, tooling fi bers had a 10 % lower value. The wettability study and
50
XPS results suggested that tooling fibers should have had a better adhes ion than prepreg
fibers because it had a higher surface free energy, Lewis acid 1 base contribution, and higher
concentration of carboxyl groups, however, this was not the case. This contradiction can
nonetheless be explained by the surface striations seen on the SEM micrographs of the
prepreg fibers, which would have improved fiber 1 epoxy adhesion by mechanica l keying [7,
23]. Despite the lack of sizing, the recycled fibers maintained their interfacial adhesion to
epoxy resin .
Table 2.8 Interfacial shear strength (T) of the carbon fibers.
~
is the variation expressed in
(%) with respect to Torayca® T700S virgin carbon fi bers.
Carbon Fiber Type
Torayca ' T700S
Prepregs Fibers
Tooling Fibers
2.6
• (MPa)
52±2
52±2
47±2
A(%)
0
-10
Conclusion
Pyrolysis processing altered the surface properties of the recyc led carbon fibers by
effectively removing sizing and resin , thereby revealin g surface topographies. Wetting and
interfacial adhesion between the surface of recycled carbon fibers and epoxy resin were
found to be predominantly affected by Lewis acid 1 base interactions of oxygenated surface
function al groups, as weil as, by mechanical interlocking. Mechanical interlocking appeared
to be the more important parameter, as striated prepreg fibers out-perfonned the smooth
tooling fibers in interfacial adhes ion w ith epoxy resin despite their less attractive surface
properties. Therefore, surface topographies are extremely important, and need to be assessed,
when predicting the performance of re-manufactured composites containing recycled carbon
fi bers, as the interlaminar shear strength of composite structural materials correlates weil with
interfacial adhesion [14-16]. Finally, recycled carbon fibers have immense potential to be
reintroduced as chopped fiber reinforcement in epoxy based composites, as they exhibited
similar performance to virgin carbon fibers.
51
2 .7
Acknow ledgements
Thi s project (identified as CRIAQ ENV -4 11 project) was supported by the Consortiu m
for Research and Innovation in Aerospace in Quebec (CRJAQ), Bell Helicopter Textron
Canada Ltd (Mirabel, Quebec, Canada) and Bombardier Aerospace (Montreal, Quebec,
Canada). The authors wou ld like to thank Karen Stoeffler and Loleï Khoun from the National
Research Counci l of Canada for the ir help and advice.
2.8
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App lications: Tech nology Review and Market Outlook. Waste Management.
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[10] Hyde JR, Lester E, Kingman S, Pickering S, Wong KH. Supercritical Propanol, a
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2006
CHAPITRE III
CARDED RECYCLED CARBON FIBER MATS FOR THE PRODUCTION OF
THERMOSET COMPOSITES VIA INFUS ION 1 COMPRESSION MOLDING *
Stefan Andj elic 1, Loleï Khoun 2', Nathali e Legros 2' , Judith Robergé, Steen Brian Schougaard
1
Chemistry Departm ent, Un iversité du Québec à Montréal
2 101 Ru e Jeann e-Mance, Montreal, H2X 2J6, Quebec, Canada
2
N ation al Research Council Canad a
75 boulevard de Mortagne, Bouch ervill e, J4B 6Y4, Quebec, Canada.
3
Bell 1-lelicopter Textron Canada Limi ted,
12800 rue de l'Avenir, Mirabel, J7J 1R4, Quebec, Canada
* Corresponding auth ors:
Lo lei Khoun
e-mail : Lolei.Khoun@ imi .cnrc-nrc.gc.ca
Telephone: (00 1) 450-641-5435
Fax: (00 1) 450-64 1-51 05
Nathalie Legros
e-mail: athal ie.Legros@ imi.cnrc-nrc.gc.ca
Telephone: (00 1) 450-64 1-5866
Fax: (00 1) 450-64 1-5 105
Steen Brian Schougaard
e-mail : schou gaard .steen@uq am .ca
Telephone: (00 1) 5 14-987-3000 ext. 39 11
Fax: (00 1) 5 14-987-4054
*This arti cle has been accepted, and published in SAE international.
1
'
55
3.1
Abstract
The use of carbon fiber reinforced thermoset composites has doubled in the last decade
raising questions about the waste generated from manufacturing and at end-of-life, especially
in the aircraft industry. In this study, 2.5 cm long carbon fibers were recovered from
thermoset composite waste using a commercial scale pyrolysis process. Scanning electron
microscopy, density measurements, single filament tensile testing as weil as micro-droplet
testing were performed to characterize the morphology, mechanical properties, and surface
adhesion of the fibers. The recycled fibers appeared to be mostly undamaged and clean,
exhibiting comparable mechanical properties to virgin carbon fibers. A carding process
followed by an ultrasound treatment produced randomly aligned recycled fiber mats. These
mats were used to fabricate composite plates, with fiber volume fractions up to 40 %, by
infusion 1 compression molding. The mechanical properties of the plates were evaluated by
tensile and flexural testing, and were found to be comparable to an equivalent containing
virgin carbon fibers.
1
1
1
56
3.2
Introduction
In 2011 , the global demand of carbon fiber tow rose to 45 ,800 tons. The aerospace
industry accounted for 6,410 tons representing approximately 15 % of the carbon fi ber
market [1]. Carbon fibers are mainly used as reinforcement in polymerie matrices to create
composite materials with higher strength to weight ratio and higher fatigue resistance than
metals. In the past decade, the use of these carbon fibers reinforced plastics (CFRPs)
increased significantly in aerospace with the development of the Boeing 787 Dreamliner and
the Airbus A380 programs containing approximate ly 50 wt. % and 20 wt. % of CFRPs
respectively [2] . This increase, however, has generated a significant amount of CFRP waste
estimated at 3,000 tons per year in North America and Europe [3]. Currently, the vast
majority of composite waste in North America is sent to landfills; therefore, aircraft
manufacturers are under pressure to reduce waste through recycling or reuse, affecting both
in-process waste and end-of-life disposai.
Environmental concerns have lead to strict management conditions with respect to
composite waste especially in the European Union (EU). Since 2004, the Landfill Directive
(1999/31/EC) [4] has rendered the disposai of composite waste to landfills illegal in many
EU countries. Meanwhile, extended producer responsibility has set recycling targets for many
types of waste. One important example is the end of !ife vehicle directive (2000/53/EC) [5],
which states that after 2015 ; only 5 wt. % of an end-of-life vehicle can be sent to landfills.
Therefore, recycling composite waste has been the subject of much investigation over the last
15 years. Y et, carbon fiber reinforced thermoset composites continue to be difficult to recycle
[2, 6, 7], as they are a complex mixture of different materials such as thermosetting polymers,
carbon fibers, and fillers; they may also contain foam cores, metal inserts, wire meshing,
paints and other contaminants. Furthermore, the cross-linked nature of thermosetting
polymers prevents remolding.
Severa! recycling technologies have been proposed and developed for CFRPs. They
can be classified in two broad categories; mechanical grinding and fiber reclamation [2, 8].
Currently, fiber reclamation has gained momentum because of its ability to recover high
57
quality carbon fibers by employing either a chemical or thermal process to break down
thermosetting resin . Fiber reclamati on is particularly suitable for CF RPs due to the hi gh
chemical and thermal stability of carbon fibers [2, 8]. The most common fiber reclamation
process is pyro lys is [2, 8, 9]. It is defined as the thermal degradation (400 - 700 °C) of
organic material (i.e. polymerie matri x) in an in ert environment (usually CO, C0 2, or N 2) .
Other fi ber reclamation technologies inc lude catalytic conversion [8, 10, 1 1], fluidized bed
reactor [2, 8, 12, 13] and supercritical tl u ids [ 14, 15].
In addition to the legislative " push" factor, another driving force for deve loping fiber
reclamati on technologies is the sav ings in terms of energy of prod uction. Manufacturing
virgin carbon fi bers requires a tremendous amou nt of energy estimated at 55 kWh 1 kg to 165
kWh 1 kg [2] . Recovering carbon fibers from CF RPs, on the other hand , requires only around
3 kWh 1 kg to 10 kWh 1 kg [2] . Therefore, economie viability of recyc ling CFRPs can be
achieved if applications can be found for recyc led carbon fi bers. To this end, the feasibi lity of
using carded recycled carbon fiber mats and epoxy resin to fabricate thermoset composite
plates by infusion 1 compression mo lding was investigated in this study.
3.3
Materials
3.3.1
Carbon Fibers
Carbon fi bers were recovered from a 100 kg sampl e of carbon fi ber reinforced
thermoset com pos ite waste genero usly donated by Bell Helicopter Textron Canada Ltd
(BHTCL: M irabel, Quebec, Canada). This samp le represents an actual sample of the waste
composition generated by the Canadian aerospace industry. It contained carbon fiber
prepregs (cured and uncured) based on epoxy and bi smaleimide resins, and tool ing parts
made from carbon fiber reinforced epoxy w ith trace amounts of silicone. Pyro lysis was
performed at Materials Innovation Technologies (MIT: Lake C ity, South Carolina, United
States) using their commercial scale batch pyrolysis oven. Before pyrolysis, the waste was
sorted and eut into 2.5 cm x 2.5 cm fragme nts to limit the fiber length distribution, thereby
controlling the overall uniformity of the recycled fibers. Pyrolysis was performed at low
temperatures (< 400 °C) under a control led atmosphere, and the residence ti me was adjusted
58
as a function of the material to be pyrolyzed. Recycled carbon fibers were obtained from
prepregs and tooling. Toray T700SC (sized, tensile modulus: 230 GPa, ten sile strength : 4,900
MPa) virgin carbon fi bers were chosen as a reference material , and eut into lengths of 2.5 cm.
3.3.2
Resin
PRJSM™ EP2400, produced by Cytec Engineered Materials, is an infusion grade
epoxy used to fabricate the carbon fibers 1 epoxy plates, with processing properties as listed
in Table 3 .1.
Table 3.1 Properties of the infusion grade epoxy PRJSM™ EP2400 produced by Cytec
Engineered Materials.
Properties
Injectable Temperature (oq
Cure Temperature ( 0 q
Dry Tg (room temperature, dry)
Wet Tg (48 hour water boil , wet)
Toughness
C ured Resin Density (g/cm 3)
3.4
Experimental
3.4.1
Characterization ofthe Carbon Fibers
PRISM™ EP2400
70
180
179
163
Very Hi gh
1.24
Fi ber surface morphology was probed usin g a Jeol GSM 61 00 scannmg electron
microscope (SEM) operating at 10 kY. Fiber diameters were measured using lmageJ software
[16]. Reported values are the average of 5 samples for each fiber type. The prepreg fiber
density was measured using a gas pycnometer (Humipyc from InstruQuest, gas: helium,
measurement pressure: 210 kPa ± 3 Pa, stabilization time: 300 s, temperature: 21.5 ° C,
relative humidity: 17 %). Reported values are the average of 3 measurements. Micro-tensi1e
testing was performed on mono-filaments according to ASTM D3379 [17] using an lnstron
Microtester equipped with a 2N Joad cell. A gage length of 10 mm and rate of 1 mm 1 min
were used. Reported values are the average of 30 samp les for each fiber type. In ali cases,
error bounds represent the 95 %confidence limits for a student-t distribution.
59
3.4.2
Characterizati on of the carbon fibers 1 epoxy adhesion
Micro-droplet testing [1 2, 18, 19] was used to quantify the interfacia l shear strength
('r), i.e. the adhes ion between the fiber and epoxy matri x. A normal fo rce was applied on a
micro-droplet of res in using shearing blades that pull the resin off the fib er. Assuming a
cylindrical model, the interfacial shear strength is calculated by:
r = F /n:Dr L
(3 . 1)
where F is the debonding force, Dr is the fi ber di ameter, and L is the embedded length.
Sam pies were prepared by gluing the end s of carbon mono-filaments onto 4 cm x 1 cm
paper templates with a punch hole through th e middl e. Elliptical epoxy droplets were applied
onto the monofil aments using a fin e metal applicator conn ected to a heated soldering iron.
Samples were cured in an oven for 2 hours at 180 °C. Droplets with embedded lengths
varyin g between 20 !lm to 50 !lm were chosen fo r testing. Observati ons were made usin g a
N ikon Ec lipse SOi optical mi croscope connected to a Qlmagin g Go-3 camera, and
meas urements were made using lmageJ software calibrated w ith a Pyser-SG I S8 stage
micrometer grat icule. A caliper attached to a Mi cos MT-65 linear stage served as shearing
blades. The caliper opening was set to 10 !lm and the speed was set to 0.1 mm 1 min . Force
measurements were acquired using a Mettl er To lledo AB135-s/FACT balance conn ected to a
computer using LabView software. Reported values are based on 15 observations for each
fi ber type.
3.4.3
Carbon fibers 1 epoxy composite plates fabr ication
Recycled carbon fi bers were transformed from a "fluffy" material to a mat by the
follow ing procedure. A roto-carder separated, interlocked and partly ali gned the fi bers. To
remove surface impurities and debri s, the fibers were placed on a 25 cm x 3 1 cm fram e,
subjected to ultrasonic treatment for 5 minutes, and washed with disti lled water. The resulting
mats were dried in an oven at 115
oc
fo r 24 h to remove res idual water. Upon visua l
inspection, fibers appeared to be evenly distributed throughout each mat. The mats had a
60
mass of approximately 19 g. A similar method was used to prepare mats containing virgin
carbon fibers.
As shown in Figure 3.1 , carbon fibers 1 epoxy plates were fabricated by a combinati on
of infusion 1 compression moulding. Mats were laid on an a luminium tool, and a peel ply and
fl ow distribution medi a were placed over them. A vacuum bag was used as formable matched
mold . After degass ing, epoxy was injected at 80
oc via a heated
injection line, and vacuum
was applied at the end of the plates. Once entire ly impregnated w ith epoxy, plates were
placed in a heated press for 2 hours at 180 °C, and compressed to 3 mm with a pressure of 60
tons.
60Tonnes
Res in inlet
Resin flow
Vacuum vent
Infusion
Compression 2 hours at 1802C
Figure 3.1 Schematic representati on of th e infusion 1 compress ion mouldin g process.
3.4.4
Characterizati on of the carbo n fibers 1epoxy composite plates
Test spec imens were eut from the plates by water j et saw (F igure 3.2). Density
specimens were co llected at pos itions A, B, C and D, and poros ity specimens were co llected
at positions A', B' and C'. Tensile and flexural specimens measured 25 mm x 250 mm x 3
mm and 12.5 mm x 64 mm x 3 mm respective ly.
61
}
1
Flexion
1
Density/Microscopy
1
1
l
1
1
1
Tension
Figure 3.2 Geo metry and pos ition of th e test spec imens eut fro m the carbon fibers 1 epoxy
plates.
Fiber volume fraction . The fiber vo lume content (v1 ) was control led by the mass of
fib ers used per plate (number of mats per plate), and is cal cul ated by:
(3.2)
where m1 is the mass of fi bers, Pt is the fiber density (as measured fo r the recyc led
3
fi bers and 1.80 g 1 cm for the virgin fibers), mm is the mass of epoxy and Pm is the epoxy
density ( 1.24 g 1 cm3 for PRISM™ EP24 00).
Density. The experimental plate density (P,c,l) was measured by we ighing sampl es in
water and air, and is calcul ated by:
Pc,1 =
mc,air
mc,air - mc,water
* PH 2 0
(3.3)
where mc,air and mc,water are the specimen masses in air and in water respectively,
and PH 2 o is the water density (0.9977 g 1 cm at 22 .5 oc [20]).
3
Based on the experimental fiber volume fraction determined m equation 3, the
theoretical plate density (Pc,z) is calcu lated by:
62
(3.4)
Porosity. Polished cross-sections of recycled carbon fi bers 1 epoxy plates were probed
by SEM in order to confirm the presence of porosities, and to examine the distribution of
fibers within the material.
Mechanical Properties. The plates were tested under uniaxial tension according to
ASTM 03039 [21] using an lnstron 5582 equipped with a 100 kN cell; the applied crosshead
speed was 2 mm 1 min. Flexion tests (3-point bending) were performed according to ASTM
0790 [22] using an Instron 1123 equipped with a 5 kN cell ; the applied crosshead speed was
1.3 mm 1 min with a span of 48 mm . Reported tensile and flexural values are the average of 5
measurements for each plate.
3.5
Results & Discussion
3.5.1
Characterization ofthe Carbon Fibers
SEM micrographs (Figure 3.3) show that the prepreg and tooling fibers were generally
clean and appeared relatively undamaged having no obvious cracks. Their diameters
measured 6.5 ± 0.8 11m and 6.5 ± 0.9 11m respectively. Prepreg fibers exhibited surface
striations designed to improve their adhesion with epoxy, and residual resin was often
observed, probably due to a lack of optimization of the pyrolysis process (the process was
optimized for epoxy composites, whereas the prepreg waste contained both epoxy and
bismaleimide resins). The tooling fibers showed sorne loose debris and no surface striation.
The average density of the prepreg fi bers was determined by pycnometry to be 1.75 g 1 cm
close to value of the Toray fi bers ( 1.80 g 1 cm\
3
,
63
a)
b)
Figure 3.3 SEM micrographs ofthe recycled carbon fi bers from a) prepregs, b) tooling
The recycled fibers from prepregs and tooling had a tensile modulu s of 160 ± 20 GPa
and 170 ± 10 GPa, and a maximum tensile strength of 3400 ± 400 MPa and 3800 ± 200 MPa,
respectively (Figure 3.4). When compared to the virgin fibers , average differences of around
- 10% to- 5% in tensile modulu s and- 22% to- 13% in maximum tensile strength were
observed. Tooling fibers offered a better mechanical performance than prepreg fibers,
although prepregs contain high performance aerospace grades of carbon fi bers, white tooling
composites generally contain industrial grades of carbon fibers . This result may be due to
process variations that can occur during recycling. Therefore, further optimization of the
pyrolysis conditions (temperature, residence time, and atmosphere), with respect to the type
of composite waste being treated, shou ld contribute to further improving the properties of the
fibers. Overall, the recycled fibers retained most oftheir mechanical properties.
64
l!l Tensile Modulus
ti
Q_
w
DT ensile Strength
200
5ooo ·
180
4500
160
4000
140
3500
120
3000 ti
100
2500 ~
80
2000 tl
60
1500
40
1000
20
500
a..
.
Ë
0
0
Prepreg s
Tooling
Toray T700SC
Figure 3.4 Tensil e modulus E (GPa) and maximum tensile strength <>max (MPa) of the
recyc led carbon fi bers fro m prepregs and too ling, and virgin carbon fi bers fro m Toray
T7 00SC.
3.5.2
Characteri zation of the carbo n fiber 1 epoxy adh es ion
Figure 3.5 plots th e fo rce at debonding versus embedded length of the microdroplet
data. Regression analys is produced a linear trend fo r each fiber type; thu s, the interfac ia l
shear strength was ca lcul ated from:
(3. 5)
r =/5 /nDr
where
/5
is the s lope of the
F vs . L regression
recycled fibers, 7 J.l.m virg in fi bers).
curve,
Dr
is the fi ber diameter (6.5 J.l.ill
65
0.06
F = 0.00 11 L
R' = 0 .91
0.05
0.04
•
• •
~
...02l
0.03
••
•• •• •
•
u.
0.02
0.01
0
20
25
30
35
40
45
50
Embedded Length (IJm)
Figure 3.5 Force (N) versus Embedded Length (J..Lm) of the recycled carbon fi bers
from prepregs for the microdroplet test.
When compared to the virgin fibers (Table 3.2), no difference was observed in the
interfacial shear strength values for prepreg fi bers, wh ile, on average, too lin g fi bers have a 10
% Jower value. T hi s differe nce may be exp lai ned by the surface striat ions seen on the SEM
micrographs of the prepreg fi bers, which could improve fi ber 1 matrix ad hes io n. Despite the
Jack of sizi ng, the recycled fi bers maintain the ir interfacial properties.
Table 3.2 Interfacial shear strength ('r) of the recycled carbon fibers from prepregs and
tooling, and virgin carbon fibers from Toray T700SC . D.. is the variation expressed in % with
respect to the Toray fi bers.
Carbon Fiber type
Toray T700SC
Prepregs Fibers
Tooling Fibers
-r (MPa)
A(%)
52±2
52±2
47±2
-10
0
l
66
3.5.3
Characterization of the carbon fiber reinforced epoxy composite plates
Table 3.3 lists the carbon fibers 1 epoxy plates fabricated by infusion 1 compression
moulding. Three plates with prepreg fibers, three plates with tooling fibers, and two plates
with virgin fibers were fabricated. Plates Tl and NR4 were not mechanica lly tested. The fiber
volume fraction (v1 ) varied from 23 % to 40 %.
Table 3.3 A List of the carbon fibers 1 epoxy composite plates produced by infusio n 1
compression moulding.
Vr
Wr
(%)
(%)
Pl
P2
P3
38
36
40
47
44
50
Tl
T2
T3
23
28
34
30
35
42
NR3
40
50
NR4
38
47
Material
Sam pie
Epoxy 1 Prepreg Fibers
Epoxy 1 Tooling fibers
Epoxy 1 Toray T700SC
Figure 3.6 di splays the composite density along the injection direction of each plate.
Variations in density are likely due to the presence of porosities in the plates as we il as a
difference in fiber distribution from one position to another. The presence of porosities was
confirmed by SEM micrographs of plates P3 and T3 (Figure 3.7); voids seemed to be evenly
distributed throughout P3 , wh ile in T3 , they are mainly observed at the outlet position C ' .
67
1.80 . , . . . - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - .
oTheoretical density
I!I Position B
oPosition C
~!! Position D
œPosition A
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
P1
P2
P3
T2
T3
NR3
NR4
Figure 3.6 Variation of composite density along the injection direction for the carbon fi bers 1
epoxy plates .
68
P3
T3
A'
B'
C'
Figure 3.7 SEM micrographs of the polished cross-sections along the injection direction of
plates P3 and T3.
69
Tensile (Figure 3.8 and Figure 3.9) and flexural testing (Figure 3.1 0) showed, as
expected, higher fiber volume fractions lead to better mechanical properties. The addition of
recycled fibers in the plates increased the tensile and flexural modulus, on average, by a
factor of at !east 6, while the maximum tensile strength and flexural strength at yield
increased by a factor of at !east 2 when compared with pure epoxy. These results confirm that
the recycled fibers act as reinforcement, and not as simple filler. For the same volume
fraction , the virgin fibers 1 epoxy plate (NR3) exhibited slightly better mechanical properties
than the plates containing recycled fibers. This difference is attributable to; the inherent
mechanical performance of the carbon fibers , the overall fi ber and void distributions within
the plates, as weil as the fiber 1 matrix adhesion (presence of sizing on the virgin fibers).
Therefore, the quality and performance of the plates containing recycled fibers should be
improved by increased control over the fiber volume fraction (via composite thickness) and
void content, increased homogeneity of the recycled fi ber mats, and incorporating an epoxy
compatible sizing at the surface of the recycled fibers .
Epoxy
P1
P2
P3
T2
T3
NR3
(38 %) (36 %) (40 %) (28 %) (34 %) (40 %)
Figure 3.8 Tensile modulus E (GPa) of the carbon fibers 1 epoxy plates.
70
l!i! Tensile Strength
o El ongation
at Break
8
300
7
250
6
200
5
Cil
0..
4~
~x 150
.c
""
Ë
b
3
100
1---
2
50
~
0
Epoxy
0
P1
P2
P3
T2
T3
NR3
(38 %)(36 %)(40 %)(28 %)(34 %)(40 %)
Figure 3.9 Maximum tensi le strength
O"max
(MPa) and elongation at break
Eb
(%) ofthe
carbon fi bers 1 epoxy plates.
I!I Fiexu ral Modulus
30
600
25
500
20
400
1
Cil
~
o Flexural Strength
15
Cil
0..
300 ~
w
10
200
5
100
0
~
Epoxy
0
P1
P2
P3
T2
T3
NR3
(38 %) (36 %) (40 %) (28 %) (34 %) (40 %)
Figure 3.10 Flexural modulus E (MPa) and flexural strength at yield
fi bers 1 epoxy plates.
O"y
(MPa) of the carbon
71
3.6
Conclusion
Ln thi s study, carbon fibers were recovered fro m carbon fï ber reinfo rced thermoset
composite waste generated by the aircraft industry using Materia ls Innovation Techno logies
commercial scale pyro lys is process. Electro n mi croscopy, density measurements, mono fil ament tensile testing and mi cro-droplet testing determined that the recyc led carbon fi bers
retain most ofth eir mechanical and surface adhes ion properti es. The feas ibility of fa bricatin g
recyc led carbon fiber reinfo rced therm oset compos ites was a lso demonstrated. A cardin g
process prod uced homogeneo us recyc led fiber mats that were subseq uently manufactured
into compos ite plates by infusion 1 co mpression mouldin g w ith epoxy. Fiber vo lume fract ions
up to 40% were obtained. Tensile and fl exural testing determin ed that plates containin g
recyc led fi bers exhibited better mechani cal properties th an pure epoxy, and si milar pro perties
to a plate containin g virgin fibers, despite the presence of poros it ies. T hi s demonstrates the
potent ial of reintegrating recyc led carbon ft bers as rei nfo rcement in new therm oset
compos ites fo r a variety of applications.
3.7
Acknow ledgements
This proj ect (identified as CRlAQ ENV-4 11 proj ect) was supported by the Consortium
fo r Research and Inn ovation in Aerospace in Que bec (CRIAQ), Be ll He li copter Textron
Canada Ltd (M irabel, Que bec, Canada) and Bombardier Aerospace (Montreal, Q ue bec,
Canada). The authors wo uld li ke to thank Karen Stoeffler, Fréderic Busnel, and Ér ic
Patenaude from the N ational Research Council of Canada for the ir advice and he lp on the
manufacturing of compos ite pl ates.
3.8
References
[1] Black S. Carbon Fi ber Market: Gatherin g Momentum. visited on 201 3-09-09:
http://www.compositesworld.com/articles/carbon-fi ber-market-gathering-momentu m
[2] Pimenta S, Pinho ST. Recycling Carbon F ibre Reinforced Polymers for Structural
Appl ications: Techno logy Review and Market Outlook. Waste Management.
2011 ;31 (2):3 78-92.
72
[3] McConnell VP. Launching the Carbon Fibre Recycling lndustry. visited on 2013-09-09:
http://www .rein forcedplastics.com/v iew /8116/launch ing-the-carbon-fi bre-recyc 1ing- industry1
[4] The Landfill Directive on Waste (1999/31 /EC). visited on 2011-07-05:
http: 11ec. euro pa.eu/en v ironm ent/waste/1 and fi Il_ index. htm
[5] Directive 2000/53/EC on End ofLife Vehicle Directive. visited on 2011-07-06:
http:/1ec.europa.eu/environment/waste/el v_ index.htm
[6] Pifiero-Hernanz R, Garcia-Serna J, Dodds C, Hyde J, PoliakoffM, Cocero MJ , et al.
Chemical Recycling of Carbon Fibre Composites Using Alcohols under Subcritical and
Supercritical Conditions. Journal of Supercritical Fluids. 2008;46(1 ):83-92.
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Recycling by Pyrolysis ofThermoset Composites: Characteristics of the Liquid and Gaseous
Fuels Obtained . Fuel. 2000;79(8):897-902.
[8] Pickering SJ. Recycling Technologies for Thermoset Composite Materials-Current Status.
Composites Part A: Applied Science and Manufacturing. 2006;37(8): 1206-15 .
[9] Sekula R, Leszczynski S. Utilization of Scrap Thermosets Using Pyrolysis. Energy
Sources, Part A: Recovery, Utilization and Environmental Effects. 2009;31 ( 1):76-85.
[1 0] Allred RE, Busselle LD. Tertiary Recycling of Automotive Plastics and Composites.
Journal of Thermoplastic Composite Materials. 2000; 13(2):92-1 01.
[11] Gosau JM, Wesley TF, Allred RE. Integrated Composite Recycling Process. SAMPE
Technical Conference. 2006
[12] Jiang G, Pickering SJ, Walker GS, Wong KH, Rudd CD. Surface Characterisation of
Carbon Fibre Recycled Using Fluidised Bed. Applied Surface Science. 2008;254(9):2588-93.
[13] Pickering SJ, Kelly RM, Kennerley JR, Rudd CD, Fenwick NJ. A Fluidised-Bed Process
for the Recovery of Glass Fibres from Scrap Thermoset Composites. Composites Science and
Technology. 2000;60(4):509-23.
[14] Yuyan L, Guohua S, Linghui M. Recycling of Carbon Fibre Reinforced Composites
Using Water in Subcritical Conditions. Materials Science and Engineering A. 2009;520(12):179-83.
[ 15] Hyde JR, Lester E, Kingman S, Pickering S, Wong KH. Supercritical Propanol, a
Possible Route to Composite Carbon Fibre Recovery: A Viability Study. Composites Part A,
App lied science and manufacturing. 2006;3 7( 11 ):2171.
73
[ 16] Imagej: Image Processing and Analysis in Java. visited on 2013-09-09:
http: //rsbweb.nih.gov/ij /
[17] ASTM Standard 03379. Standard Test Method for Tensile Strength and Young's
Modulus for High-Modulus Single-Filament Materials. ASTM International ; 1989.
[18] Jiang G, Pickering SJ, Lester EH, Turner TA, Wong KH , Warrior NA. Characterisation
of Carbon Fibres Recycled from Carbon Fibre/Epoxy Res in Composites Using Supercritical
N-Propanol. Composites Science and Technology. 2009;69(2): 192-8.
[19] Miller B, Muri P, Rebenfeld L. A Microbond Method for Determination ofthe Shear
Strength of a Fiber/Resin Interface. Composites Science and Technology. 1987;28( 1): 17-32.
[20] Perry RH, Green DW. Perry's Chemical Engineers' Handbook: McGraw-Hill ; 2008.
[21] ASTM 03039. Standard Test Method for Tensile Properties of Polymer Matrix
Composite Materials. ASTM International; 2008.
[22] ASTM 0790 . Standard Test Methods for Flexural Properties of Unreinforced and
Reinforced Plastics and Electrical Insulating Materials. ASTM International ; 201 O.
~ -----
CHAPITRE IV
CONCLUSION
In this work, chopped recycled carbon fibers from prepreg and tooling were recovered
from carbon fiber reinforced thermoset composite waste generated by the Canadian aircraft
industry, using Materials Innovation Technologies commercial scale pyrolysis process.
Pyrolysis processing altered the surface prope1ties of the recycled carbon fibers by effectively
removing sizing and resin , thereby revealin g surface topographies. The mechanical
performance of the recycled fibers were comparable to that of the virgin fibers, with a
decrease in tensile modulus of < 10 %, a decrease in tensile strength of < 22 %, and a
decrease in interfacial adhesion to epoxy res in of < 10 %.
This work demonstrated that recycled carbon fibers can be reintegrated in thermosetting resin
producing high quality composites. The epoxy 1 recyc led carbon fiber plates, fabricated by
infusion 1 compression molding of carded recycled carbon fiber mats, had a comparab le
mechanical performance to a virgin equivalent with a decrease in tensile modulus and
strength of < 10 %; however, severa! recommendations can be made to optimize the quality
and performance of the fabricated composites, as weil as, the molding process:
- The quality of the mats has to be improved to reach a more homogeneous distribution
of the recycled carbon fibers . Moreover, preferential ali gnment of the fibers can 1mprove
anisotropie properties ofthe fabricated composites.
- The infusion 1 compression molding process needs to be optimized to better control
the fi ber volume fraction and void content.
- The incorporation of an epoxy compatible sizing at the surface of the recycled carbon
fibers should be investigated to enhance adhesion at the fiber 1 epoxy resin interface.
75
Moreover, surface topographies of the recycled carbon fibers need to be assessed prior to
molding, as they have a significant effect on interfacial adhesion with epoxy resin.
- Scaling-up of fabrication process. This includes cleaning and preparation of the
recycled carbon fi ber mats, as wel l as, molding of the final composite piece.
In addition, Sheet Molding Compounding (SMC) should be investigated as an
a lternative method for manufacturing epoxy 1 recycled carbon fiber composites, since this
fabrication method all ows for the incorporation of higher fi ber contents, and leads to a better
consolidation ofthe material.
Finally, this thesis confirms the huge potential of re-manufacturing high quality
thermoset composites from recycled carbon fibers . Such materials might be suitable for
app li cations in the aerospace industry or in other markets.
APPENDIXA
SUMMARY
During my master's, I had an intern ship from August 20 Il un til February 20 12 at the
National Research Council Canada (NRC), under the superv ision of my co-sponsors Nathalie
Legros and Karen Stoeffler. T worked on a project identified as CRIAQ ENV -411 , which was
supported by the Consortium for Research and Inn ovation in Aerospace in Quebec (CRIAQ),
Bell Helicopter Textron Canada Ltd. (Mirabel, Quebec, Canada) and Bombardier Aerospace
(Montreal, Quebec, Canada). This project resulted in the following work:
- A report entitled "Recyc ling of T hermoset Compos ites Wastes from Aerospace Industry :
Feasibility Study and Proof of Concept" was produced, and is currently und er a
confidentiality agreement. The portion di scuss ing compos ite waste legislation is presented in
Section A.l of the appendix. In addition, it was presented as a poster at a CRIAQ conference.
•
Stoeffler K, Khoun L, Legros N , Andjelic S, Schougaard SB, Roberge J, Chowdhury
S, Corrigan J, Dezombre J, Jordan A, Oudi ehani K. Recyc ling of Thermoset
Composite Wastes From Aerospace Industry: Feasibility Study and Proof of
Concept. 1Oth Anniversary Gala CRIAQ. 20 12 . Montreal, Que bec, Canada.
- A scientific article entitled "Effect of Morphological, Mechanical and Surface Properties on
the Wettability and Interfacial Adhesion of Recycled Carbon Fibers" is intended for
publication in the Journal of Material Science, and is reproduced in Chapter Il.
77
- A technical paper entitled "Carded Recycled Carbon Fiber Mats for the Production of
Thermoset Composites via Infusion 1 Compression Molding" was accepted and published in
SAE International, and is reproduced in Chapter III. This manu script was presented as an oral
presentation at the SAE 2013 AeroTech Congress & Exhibition, held on September 24-26,
2013 at Palais des congrès, in Montreal, Quebec, Canada.
•
Andjelic S, Khoun L, Legros N, Roberge J, Schougaard SB . Carded Recycled
Carbon Fiber Mats for the Production of Thermoset Composites via Infusion 1
Compression Molding. SAE International. 2013.
- A scientific article entitled "Polyphenylene sulfide (PPS) composites reinforced with
recycled carbon fiber" was accepted and published in Composites Science and Technology.
A copy of the article is reproduced in Section A.2 ofthe appendix.
•
Stoeffler K, Andjelic S, Legros N, Roberge J, Schougaard SB. Polyphenylene sulfide
(PPS) composites reinforced with recycled carbon fiber. Composites Science and
Technology. 2013; 84(0): 65-71.
Section A.1 covers legislation on composite waste disposai , white Section A.2
presents the published article mentioned above.
A.l
Composite Waste Legislation
2.
Thermoset composites recycling
2.1.
Government Regulation s
2.1. 1. Introduction
Govemments are currently setting up legislation in order to decrease the amount of waste thal
is produced. discarded, and disposed of. White methods may vary, the goals of waste
management are always the same : promoting thewaste management hierarchy (reduce. reuse,
recycle, recover and disposai) and reducing the amount of waste thal is sent to landfills. This
section will examine current and upcoming legislation conœming waste management in
Canada and Europe. The main locus will be on the management of thermoset composite waste.
2.1.2. Waste Management in Canada
2. 1.2. 1. Overview
ln Canada. the responsibility of managing waste is shared amongst the federal, provincial 1
territorial, and regional 1 municipal governments. The federal government is responsible for
managing the international and interprovincial movement of hazardous waste destined for
recycling or disposai. The provincial 1 territorial govemments have jurisdiction over the
transportation of hazardous waste within its boundaries, as weil as the licensing and permitting
of authorized facilities undertaking the reclamation, recycling, or disposai of waste'.
2. 1.2.2. Management of End-cf-Ufe Products in Canada
Approxima te !y 1.2 million vehicles are taken off the road every year in Canada. This amounts to
nearly 150 000 t 1 year of vehicle waste thal ends up in landfills2• Given thal the volume of waste
produced by the automobile industry far outweighs that produced by the aerospace industry; it is
sale to assume thal any legislation conceming End-of-Lite (EOL) vehicles will be a precursor for
EOL airerait legislation. Canada has lagged behind many countries in the world in addressing
this issue and there are nearly no laws in place dealing with EOL vehiclesu.
The management of other EOL products is govemed by both Extended Producer Responsibihty
(EPR) and Product Stewardship programs•. An EPR program specifically identifies end-of-lite
management of products as the responsibility of producers (e.g. brand cmners, firsl importers or
manufacturers), whereas a Product Stewardship program allocates the responsibility to
16 1
79
provincial / territorial or regional / municipal govemments. The main difference between the two
approaches is thal funding for EPR programs is provided by the producers. Therefore, if an EPR
program were developed for EOL aircrafts, it would put the responsibility of managing such
waste on airerait manufacturers.
2. 1.2.3. Waste Management in Ouebec
al Overview
ln 2008 , 13 million tonnes of waste was generated in Ouebec amounting to 1.69 t 1 capita. 52%
of this waste was treated, leaving 810 kg 1 capita of waste thal was disposed of. Therefore,
the re is an undeniable potential in further developing reclamation and recycling technologies. To
demonstrate this key point, in 2006. 2.5 million tons of the most commonly recycled residual
ma teri ais thal were recovered generated S 550 million and created over 10 000 jobs5.
ln Ouebec, waste (a.k.a. residual materials) management is govemed by the Environmental
Ouality Act (EQA, 1999)6 and enforced by the Minister of Sustainable Development,
Environment and Parks. There is no specifie regulation for the management of composite
waste: thus, they are treated on a case by case basis, by applying the EOA (sections 20, 22,
and 66, Table t ) and by examining the regulations on residual materials (Regulation Respecting
Solid Wastes, Regulation Respecting the Landfilling and Incineration of Residual Materials,
Regulation Respecting the Charges Payable for the Disposai of Residual Materials) and the
regulations on hazardous residual materials (Regulation on Hazardous Materials).
Table 1. Oesaiplion of the sections 20. 22 and 66 of the Environmentaf Ouafity Ad.
Section Environmental Quality Act
No one may emit, deposit, issue or discharge or allow the emission, deposit,
20
issuance or discharge into the environment of a contaminant in a greater quantity or
concentration than thal provided for by regulation of the Govemment.
No one may erect or alter a structure, undertake to operate an industry, carry on an
22
activity or use an industrial process or increase the production of any goods or
services if il seems likely thal this will result in an emission, deposit, issuance or
discharge of contaminants into the environment or a change in the quality of the
environment, unless he first obtains from the Minister a certificate of authorization.
66
No one may deposit or discharge residual materials or allow residual materials to be
deposited or discharged at a place other than a site at which the storage, treatment
or elimination of residual materials is authorized by the Minister or the Govemment
pursuant to the provisions of this Act and the regulations.
t7 1g 3
80
bl The Residual Materials Management Policv
The Ouebec Residual Materials Management Policl provides insight into the future of residual
materi als management in Ouebec. This policy reflects the government"s intent to build a green
economy and is accompanied by a 5 year Act ion Plan. Ils main goals are to create a zero-waste
society and to dispose of only end -waste. lt includes measures (regulations, programs,
amendments, reports, etc.) thal will address th e three main challenges of residual materials
management:
Ending resource waste
Promoting the goals and achievements of the Climate Change Action Plan and of the
Ouebec Energy Strategy
Making ali stakeholders involved respon sible for residual materials management.
The quantitative goals of the Action Plan are the following:
By the end of 20 15, the amount of residu al materials sent for disposai must decrease
from 810 kg 1 capita to 700 kg 1 capita
70% of paper. cardboard, plastic, glass and metal waste must be recycled
60% of organic putrescible waste must be processed
80% of concrete, brick, and asphalt waste must be either recycled or reclaimed
70% of construction, renovation, and demolition waste from the building segment must
be sorted at the source or sent to a sorting center.
To reach these goals, 10 intervention strategies have been set up :
t.
2.
3.
4.
5.
6.
7.
Maintain the 4R-D hierarchy (reduce, reuse, recyde, recover and disposai)
Prevent and reduce the production of residual materials
Discourage and monitor disposai
Ban the disposai of organic mate rial
Make producers more responsible
Support reg ional planning and performance
Stimulate the performance of the indu striai and construction sectors
8. Choose the most efficient collection system
9. Know, inform, raise awareness, and educate
t O. Report on results
There is no mention of thermoset composite waste, EOL vehicles, or EOL airerait management
in the 5 year Action Plan. However, there are a few interesting developments. The Regulation
for the Recovery and Reclamation of Products by Enterprise extends producer responsibility for
severa! EOL products. This regulation forces companies to manage and bear the full cost of
reclamation, recycling, and disposai of their waste. Another interesting development is the
increase of landfilling fee s discussed in the Regulation Respecting the Charges Payable for the
Disposai of Residual Mate rials ~.
t8 l93
81
cl The Regulation on Hazardous Materials
1t is important to determine whether or not thermoset composite waste is considered hazardous.
The Regu lation on Hazardous Materials7 defines a hazardous material as any substance which
poses a threat to health or the environment and has the folkming properties: explosive,
gaseous, flammable, poisonous, radioactive , corrosive, oxidizing or leachable. There are also
materials thal are classed as hazardous regardless to whether or not they possess any of th e
above mentioned properties. They are :
Oil and grease
A contaminated empty container
A gas cylinder or aerosol container containing a hazardous material
A material or object contain ing 3 %wt. or more of oil or grease
A material or object containing more !han t 500 mg /kg of total organic halogens
A material contain ing polychloride biphenyls (PCBsl or contaminated by PCBs
A material or object contamina led on ils surface.
Hazardous materials may be disposed of in final disposai sites ether !han the following :
Mate rials in a liquid state at 20 'C
Mate rials thal contain a free liquid
Rammable or explosive materials
Soil having 50 mg 1 kg of PCBs or more
Mate rials physically or chemically incompatible with the materials thal oonstitute the final
disposai site
Mate rials that may, on contact with water, air or materials already in the site, form gases,
mists or fumes at levels thal oould lead to harmful effects on the health of human beings
or of ether living species or damage to the environment or to property
Mate rials and objects oontaining PCBs or oontaminated by PCBs.
ln general, thermoset oomposite waste is not considered hazardous. However, the recycling of
thermoset composites may produce hazardous by-products. For example, chemical and thermal
recycling methods transform the resin matrix into lower chained hydrocarbons that are in a liquid
or gaseous state. These by-products need to be either incinerated, oombusted for energy
generation purposes. or sold as a product because they cannet be sent to final disposai sites.
dl The Regu lation for the Reoovery and Redamation of Products by Entemrises
This regulation promotes extended producer responsibility for electronics, batteries, paints and
paint containers and mercury lamps, and will impose stringent conditions on their waste
management. lt states !hat companies must implement a recwery and re-use program for the
products they market. If they !ail to meet this obligation, they will have to pay to the Green Fund,
an amount corresponding to the difference between the prescribed and achieved rates'.
19 193
82
el Regulation Respecting the Charges Payable for the Disposai of Residual Materials
The purpose of this regulation is to prescribe the charges payable for the disposai of residual
materi als in disposai sites. !:very operator of a disposai site must pay charges of $10.88 / t of
residual materials received for disposai. ln addition, from October t " 20t0 until September 30"'
2015. an additional fee of $9.50 1 t is charged. However, no charge is payable for incineration
residue from an incinerator or for residual materials thal are sorted and recovered on the
premise !hat they will be reclaimed9 .
2. 1.3. Waste management in Europe
2. 1.3. 1 Overview
ln 2008, the European Union ŒU-27) produced 2.62 billion tonnes of waste amounting to 5.2 t 1
capita. 9t o/o of this waste was treated , leaving 468 kg 1 capita !hat was disposed of. EU 's waste
management policies aim to reduce the environmental and health impacts of waste and to
improve its resource efficiency. These policies are based on 3 principles; waste prevention,
recycling and reuse , as weil as improving final waste disposai and monitoring . The EU's 6"'
Environmental Action Plan includes waste prevention and management as top priorities. ~s
main objective is to decouple waste generation from economie activities. Therefore. with proper
measures in place. economie growth should not lead to an increase in the waste volume to be
disposed of10.
EU waste directives on landfilling and incineration have resulted in st ringent management
conditions for composite waste. Si nee 2004. the landfill of composite waste has been banned by
most EU member states. Member state policies have put more pressure on solving composite
waste management through reuse and recycling, by promoting the waste management
hierarchy and extended produœr responsibility. The EU has already set recycling targets for
many types of waste : EOL vehicles, electronics and electronic equipment, batteries, packaging,
1
demolition and construction rnaterials and municipal waste u 2•
The Landfill Directive ( 1999/3 t/ EC)' 3 is intended to prevent or reduœ the negative effects of
waste on health and the environment. ~ sets strict requirements for the operation, monitoring ,
and closure of a landfill site. This directive defines 3 types of landfills: hazardous, nonhazardous, or inert. Co-<lisposal and mixing of hazardous and non-hazardous waste is not
permitted. Additionally, ali waste must undergo treatments to decrease its volume orto remove
its hazardous nature. Therefore, composite waste is not considered an end-waste and must be
processed before disposai. Certain wastes are restricted or banned from landlills such as tires,
liquid waste and some types of hazardous and biodegradable wastes' 0•11 •
According to the United Kingdoms' waste classification scheme, composite waste is defined as
a non-hazardous rnaterial under the heading of Biodegradable Wastes and other non special
waste which can give rise to organic or other contamination and il can be disposed of in a
20 193
~--
83
landfill thal accepts non-hazardous waste ' . The landfill directive obliges Member States to
reduce the amount of biodegradable waste thal they landfill to 35% of 1995 levels by 20 16'•.
Therefore. seme EU states have set targets to progressively reduce the amount of
biodegradable waste thal is sent to landfills. Moreover, under many EU state legislations, the
landfilling of organic wastes, including plastics, is restricted or even banned. EU legislation does
not differentiate composite waste from ether types of organic wast es even though they may be
relatively inert 10·11 •
The directive on incineration (200!76/EC)' ~ sets requirements for the emission of contaminants
in the air. water. and soil. Different types of wastes are often c~ inc ine rated so thal the energy
content remains relatively constant. This ensures complete combustion and avoids unwanted
emissions. Compos~e waste can be incinerated provided thal it does not exceed the limits
provided by regulation. However, its high calorie content and the limited capacity of municipal
incinerators means thal less domestic waste, of which there·s nearly an unlimited supply, is
incinerated. Therefore, the cost of incinerating composite waste is much higher !han ordinary
waste. For ex ample, in London, the cos! of incinerating composite waste (€ 120 1t - € 150 1 t) is
approximately 5 times more expensive than the average (€ 30 1 1) 12• The residues produced by
the incineration of composite waste would be composed of inorganic lillers and libers and they
can as su ch be sentto landfills 11 •
Table 2 gives a list of relevant legislative documents regarding composite waste.
Table 2. Relevant EU legislative documents regarcing composite waste".
Document
75'442/EEC
91 /689/EEC
931259/EEC
94167/ EEC
1999131 /EC
1999/45/EC
2000/76/EC
2000/53/EC
2000/532/EC
2002195/EC
2002196/EC
Title
The Waste Framework Directive
The Haz ardous Waste Directive
The Regulation on Trans-border Shipment ofWaste
The Hazardous W aste Incineration Directive
The Landfill Directive
The Dangerous Preparations Directive
The Incineration of Waste Directive
The End-of-Lite of Vehicles Directive
List ofWaste in relation to the Waste Framework Directive 75/442/EEC
The RoHS Directive (restriction of use of hazardous substances in electrica l
and electronic Equipment)
The Waste Electrical and Elec1ronic Equipment Directive (WEEE Directive)
2.1.3.2. The End of Life Vehic/e Directive (2000153/f.C)
Every year, EOL vehicles generale from 8 to 9 million tonnes of waste in the EU. The EOL
Vehicle Directive (2000/53/EC) aims to increase the reclamation, reuse, and recycling of EOL
vehides. tt does this by imposing stringent demands on automobile manufacturers' 6 :
21 1
84
EOL vehicles alter 2006:
85 wt% must be reused, recycled , or subject to energy recovery.
Only 15 wt% can be landfilled .
EOL vehicles alter 2015 :
85 wt% must be reused or recycled.
10 wt% may be subject to energy recovery
5 wt% can be landfilled
The ferrous and non-ferrous metals account for approximately 76 Ofowt. of a vehicle and these
materials are routinely reclaimed and recycled. The more diff icult challenge is to reclaim and
recycle plastics. which make up approximately 9 %wt. of a vehicle. Therefore, due to legislation,
composite automobile suppliers may lose a portion of the ir market share to the metal industries
if their parts cannot be reclaimed or recycled'7 .
22 193
A.2
Polyphenylene Sulfi de (PPS) Compos ites Reinfo rced w ith Recyc led Carbon Fiber
Conten<o
~lb
avliable tit SciVerse SclenœDkea
Composites Science and Technology
journal homepage : www.elsevler .eom/loeat e/eompael teeh
1~
1 1 \1 \ Il
Polyphenylene sulfide (PPS) composites reinforced with recyclee! carbon
Crou:'..t;ar<
fi ber
Karen St Iller ... •. Stefan Andjcli ". Nathalie Legros ..... judith Roberge ' . Steen B. Scho ugaard "··
<4."0!:. lS houk\'Qfd dt \b'r c.loudwMtlt, Qudw. ~J bY.t
' OtF=a ofthttrat,.,., l..bw\'t'n::.t!' du Q:lib« A
t'tet~~ &ea . su::n~n.U C mr1't' 1
~ w Utk:Dpte- tumm !4:u:bl~td Jl i!O:) rwdt (lb.,,., \t:Tctd Qutbtc. ~J lJ r .t
• .~moiRumrchtourc!
ARTICLE
A.
~.,.Jtt
A.~
RK)<Ied c..llbon f1bt!f\ ....~~ tt.<IJunt'd by con.nt'fcul
rr.
pyroly~~
han CJrbon llbco•
re~nlaœd
ll.er -
dtd CJJ boo hl>f'f'\ \'\"t1t tntc<gr.u .. d lnlo J poi.YJ>hffiylrnt sulhd~ {Prs ) thtrmq>l.tSIIC rt'lln
t'A'U\
rt"W canpoundaog lotiON t'rd by 1n~ c 1 n n kS&ng . Co n~ \ dt '( co nt.11nlog 20 wt.% .tnd 4 0
1 C ~d .tJbon hbtH Y.wt' prodiJCcd 0vC"tJ8 . ltw r1bt-n 'f'\'t'C~ IOUnd lO ~ UnlftY~y da.~i'd Ill theo
polytnd ~ mJtr u. ll\t t~~ lk fli wr.lJ .lnd Cmp.l(t propH11n o lt tw co n~\ltt" S ''"" ' ' n'Jit.Ytid 11)c' recyclt'd C.&l
h r rotlnforcfd PPS co n~><H ilt" .. nhtbllt"d oo mp.at.abk m«hm.c.al pr o pot'ft~t~ to e"'J.11V.1itnt
cumpwnd< pr IXt"d u.'u lndJ.... uulgr.tdn ol \ho tt \'irgtn c.ubon t.t>tt ln Jdd1h0n.thtnn " r.l~mtlrt c
.atW~~ sho\'\'t'd ttutthi' enu
uC11C1\ d rr<ycltdurbon l~ s w.b 001 d~nmenLlJ 10 tht- inherffll ll'k'1 ·
hbtot'\. Tht r
,, .%
by
lm: c orr.po :SC M l P\~( 1
fibt-N
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f~
.ait
moh1 rum~llc' w.Ktt~ gr" I~J t fd ~ thtuH~p.l(~ lncils u y. Titt" mt"C'hJn .1l.lnd phys .li ptopt>O•i'i of
tlwo fl'(l.tunrd c.ub.>n lrben v.>t>œ 'ihown to be- co n~r.lblt" 10 thO'IC.' ol.wros pJCr gtJdt! virgin arbon
onb ne- lt. ~v 20U
......
toi. Qutbtc. c..œ.::dr:H ..k. Jhf
AB ST RACT
INFO
Ntdt hru
.
~ ft\'t'd 1 J 0'\'t'rr.~r l OU
e wd 1n rn~f'd fonn 1 MJ.y l 01J
Acrepud l Mly l OU
Av~IJ.bk
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• •
Cxtnauon
"'""
l MKN:naol prop«1v-s
Q.Jb~ttyu
rrs
C 101 1 Pubhh<d by
[bn>k"l
Ud.
1. lntroduaion
the tstabb s h~n t of rccyclmg mut(5 to cnsurc propcr conformî ty
wi th upcoming œgull t ions.
Co mp osites tuvc b«n uscd in arrt:'rdft &sign for many Yf'Jts as
they signific.mt ly rt duœ aircTJfl: wcight and fuel consu mpri on .
Compo site rcxycting h """n ! be subject of much investigation
ovcr rbe llsr d ade. Tbe rcxycling of rhonn ose r composi ros. w h ich
ûrbon liber roinforccd polymers ( CFRI's) are pa n icu llrly .I IU C-
ac cou nt for thC' l:u- est p.lM or th e acrospacc compo sit e nu t crials.
is stiJl problcm.ltic. Several mcthod s ha ve b n dC'wlop....""<i to rc-
ri vc- for thC' .:tc-rospa œ irdustry si nee 1hcy dfC' ligh t .tnd show out~
sunding mechanic.JJ propc-rriC's and corroston rcs~ UOC C'. In 20\ 1.
!he worldwide domand of ca mon libers for ·rospaa: appliGlti ons
was 70 1 and il was oc poet cd to incroaJC 10 19.700 t by 2020 Il~
Al th ough CfRPs pre-sent oomcrous Jdv.mo.gcs.. thctr IOCrt'.UIT~ use
also gmcr.-cs an incrcasing .unount of w~tc . including out ~ or~
d.lœ pre pre
manufaaurifl: cu r-otrs. tosnng rrurrrials . production tools and cnd-of~ifo componcnt s 121. ln North AmcnGl. lhore
~
currcntly nc.ar1y no le-gislation to cu mil composiœ wasrc dJS·
n rrude by
ccroin provincial govcrnmcnrs. such .lS th e provinœ or Qucbc-c
pos>l. Ho""""'· a few dovelopmon<s h....,., rcam rl y b
(Carud.l ) which lus tncrNJC<I landlillifl: f""s Il~ On the olh<Y
lund. rho EuropNn Union lus adop tedstringont managemcnrcondlrions wilh regardsro composile w.ute. limiting t beirdisposal by
llndfilling 141 and extending p roducer rcsponsibitity 15~ Tho
incrc-nirrg legislation on composilc- w
tt' managcrtll"nt rcquircs
• ( om-lp('lncbn~..lua01'1
l
~ua:
~ rcn
a (N
bn-n 'R'Dt'fflr:C'tc-lrc nrc.
mt.t. ID S ur hat rru: M"
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u
~.nrcn. tdt ~ -' n n
l l fi.I DIII \htd
cb:.d œ.~n 0. 101 ~ Ja:m-.ps:a~h. lt)1 l.OS.
(
q:m.a (
rt.
lll t'\1«1' l d
.s
ruth.:ht k-
l.~ hou~.rd '
cyde lherlllOSCI compo si res. Me<haniGll grinding 12 .6-9~ which
consists of brt'aking down tl'lc> thc rmoser com~i u.• wastr by
shrcddi:ng. crushi ng or milling. is the most rurrent mcthod for
rccyclllg fibC'r rcmforccd lhcrmoset composites. The fr.l mcnts
produ œd arc typi cally reuscd .as fillcrs in composiu:s. artificial
woods or œmmts . Fiœr cxtr4ctl0n. on the- othcr tu nd. gcncr.. cs
more valuablc products. This is pantcula:rly tnr in the ca~ or
CFRPs. sincc t he priœ of vir 10 carbon fibcrs lies l:lcrwœn
32 USD/kg and 65 USD/kg. versus 18 - 26 USD/ kg for ca rb on libers
reda rm..'<i from CFRP wasto po ~ ln addiliol\ the production of
rcxyclcd carbon fi>ors n:quires !css en< IllY !han ohe rrunufacruring
ofvirgin carbon fibcrs. making former an mvirorvncnt.1Dy attr.tc·
riveoplion 110~
Sovcral t o<hnologies allow for lhci\'Cllm.Iion ofurbon libers
from CFRP w.utr. l'yrolysis 12.6.11 - 13 ~ which consists in tho tber·
mal degradation of rbe pol ymer malnx in lhc absence ofoxygonat
remp<rarures varying from 450 C to
C. is lhe most mature
re<hnology. EI.C Carbon Fibre lld. 114) ( United Kingdom) is lhc
world"s tirso comm<rculsGllc plant for rcxycting CFRI's. Th<>y luve
rbe cap.>c ily 10 proc s 2
yo>r of composite was
using
86
continuou s pyro ly<is. Ma tt rials Inn ovati on Ttc hn oiOj;ics 1151(U nittd Slalts) lus the cap.1ci t y to proc<Ss 1300 Wear 10 22 t j'y en of
co mpos~ e w~lr usiog ba tch pyrolysis. CatJiyti c conve rsion
12.6.16.171 aims at d tcamposing the polymer matri < int o low
moltcU ior weight hydroca rbons using c hemi ca l so lve nts. 1t ope r.Ji tsa t temp.,..aturcs compristd betwre n ISO<(: and 300 •(. Adh t rtn t Ttc hnoiOj;i cs ln c. 1181 ( Unittd States) h as d ovd o ptd a batch
ca tJiytic conve rsion procrss ill t he pilot sca lt. Stsidts pyrolysis
and c a~1lyti c conve rsion. two othe r promi sing rtcycling ttchnolo~n deve lopro but are rurrt ncly o nly availabk .u I lle
gics h
llbor.ll ory sc al e. The fluid is td btd proccss 12.6,19-2 11 consi siS of
a faSl th ermal oxidative dtc omposirion of t he polymer mat rix betwrc n •ISO•C and 550 •(. wh.,..oas tho suporcriri cal fluid pro ctss
12..22-251 in volvrs the use of a so tvent mainLJinrd in a supe!rcritic.tl ru tt to dtcompost tho polymer m.Jirix. Tho proptrt its of the
rtcycltd carbo n fi be rs art rightly linkt d to th o rKiaimiog pro ctss
ustd. lt h JS b n rrporttd tha r carbon fib t rs rtc ll imtd by pyrolysis
1how I~U t rtducti on in to nsilt stre ngth when pro ctssed undtr
500
16.11 ~ Fo r mol'l' informati on. a th orough rcvi ow of the
cx istiog th erm ose t r ychog ttchnoiOj;ics lus bren rtcenlly pubfi shtd by Piment! .tnd l'inho 121Aso fn ow. rtcyd td ca rb on fi be rs have bre n succcssfully re ustd
as rt info rce men!S in stvt rallhermos ring rosins ( e-~;- epoxy 126281) and thcrm oplas ti c r ins ( e.g. polyethylen e 1291. polypro py~
ene l.l0-32). polyamid e J 33~ polyethcrimid e IBia nd poly ether
C!her kotont 133J). McNaUy et •1. 1291 1\'porttd • 1 sm: incl'l'JS<!
in polyc thyltne lr nsüe modul us .nd a 27.51: inc rNst in œns üt
stre "!;th using 30 wl .ll. mül td rtcycltd e<~ rbon fibers. Wo n g et al.
1321 rrporttd a 7SX incrtJS<! in polypropyl t nt tm silo st rcngrh
usi ng 30 wt.1:short rtcyc ltd arbon fi bers. ln thise olS<'. thta dd•tion
of cMc fully S<!l td malti c anhydride gratltd coupling <1!;< n iS allov~ a n improvement o f the ad hesion al th e fiber{m.Jirix inl <r·
r, e. rcsu ltinl; in furthr r c nha nce ment s in tr nsile stre ngth.
ln this work. a l'l'pl'l'st nttrivo sa mplt of ae rosp.Jct thcrmo se t
compos it e waSl t w as coll ttd and pyrolyztd at th e co mm crc iJI
scalt. Th e rtc!a imtd carbon fibcrs wtro ca rtfully charactt ri ztd before bci ng inco rpor.u ro u rcinforcr mc.-nts in a polyphmyl cnc suJ·
fidc (PPS ) thl:rmoplasric rrutrix by twin scrcw extru sion PPS is one
of the most popular th t- rmoplasti c:s for acros p;aœ appli c.l t ions duc
to its rrosonablc cosr. procr ssing tanpcrarurc. high stiffncss and
turdn c.ss. exce llent rcs istancc- 10 solvcnr s ard low Oammabili ty.
The rccyclcd c.ubon fibcr rcinforccd rrs compo sit es we rc rtlC"Chan-icaDy and t hcrrrull y charaa crizcd Thci r propcrti cs wc re cornpar cd t:o thosc of cquiva~n l composiœs bascd on Vi!l;in o rbon
fibor.
2. MatcrWs
Ry ton P- 6, a low vi scosiry PPS grade productd by Ch ron Phiti ps ( mclrflow ind ex:380 10 mina t 3 16'C/5kg) w:ISstl ttd as
th e poly ~ rie m.11 ri x ro fa bricatc the c.J rbon fi ber rci nforcOO tht'rmoplas ric composi tes.
RNydtd ca rbon fib c~ werc rtclaim od from a 100 kg S.l!Tl pl c of
ca rbon fi ba- rt:i n forctd t hcrmos n wastc providtd by Bt D Hcticoptrr Tcxtron û n.>rla lld. ( Mirabe l. Quob..'C, Can ada ~ This wasr.
samplc w as rcprc.scnt.tri vco ft l'lc acrual wasœ co mposi tion gcncr.;r cd by ttr C.m.uti Jn .tt'rospJCc industry. Ir rru inly containc'd ca rbon fibe r prrpc
( ruœd and unruœd ) b.lstd on epoxy or
bisrrulcimidc rc-sins.. Jnd fi nished parts made of carbon fi ber rei n-fort'f'd epoxy. The fin ishcd pan sa Iso contlinOO contaminanl ssuch
as primer or pai nl The pyrolysis wJS pctfonn td at Mat trials Innokc O ty. Sou th Ca roli ru. Uni tod St.tt <S ) using
vat ion Ttchno!ogics
th <i r commercial ba teh pyrolysis ovcn. Beforc pyrolysis. t ht waSlt
was sort cd and ru t into 6 mm ' 6 mm frag~ n ts. Thc- w.lStc- fragmcniS be l'ore and afltr pyrolysiSJrt shawn in Fig. 1. Pyrolysis WJS
pt rfo i1Titd belO\'/ •100 ' ( und er co ntroUtd atmosphtre Th e dura -
rion of th e procrss was ,a dju sttd as a fu ne ri on of the m.Jtcrial to
be pyrolyzl'd according to rhc cxportiS<! devc loptd by Ma r.,..ials
lnno v.Jiion Tec hn oiOj;i<s. Rtcyc lcd ca rbon fibe rs wero obaintd
from p<t p l'l'gs and from finisht d p a ~ s. bOlh with anavcragc lt nl:lh
of 6 mm. The rKydtd carbon fib"'s w t rt c lrun ed by s uc cessive
watrr washin;s in volvin s: uJtn~ son ic ati o n srcps to rt movc any
pyrolysis residucs. and furthcr drit'd ro climiru tr residtul
moinurc.
As1he r«ycl«i ca rbon fi bers origin.u c from difTrrrnt f«'dstock.
1hcy art co mposed of vario us types of ca rbon fib crs. Hcnœ. it w.t.s
not p:u.si bl t' toa.sst"ss prcOsclythccfTt'CI oftht'rrdaiming proccss
on thcir propcrri cs. ln th is si tuation. the performanc e of th e rec y·
c ltd fi bers wascomp.1rtd t o 1 hat ofrypi ca l ca rbo n fi be rs: aerosp e
: si ztd ) wcrc sup grade, long vi rgin ca rbon fib t rs (Torayca• T7
pl itd by Toray. whilc indu stri.11 grade. sh ort virg in ca rbon fi be rs
( Pa ntx 35: unsi ztd: nomin a ll t ngth: 6 mm) wcrc obuintd from
2o kck.
3. Exptrimtntll
3. 1. Ora raat n!Dnm of t h#: rtc)Cied carl>on fi bers
The surfacr of the- rccyc lcd carbon fibcrs wa.s 1nvest ig.urd using
a jeol GS M 6 100 sca M ing e ltctron mic ro sropr ( SEM ) opera tin g at
10 kV. Th e d t nsi ty of th e rtcyc ltd carbon Abe rs was meas u rod
usir; a g.ts picn omcc cr Humypic from ln struQucst T'he I'TlC'asurcmr nt s wrre caiTied out ~ 2t0kPa llSing a stlbil izat ion rime of
l OO s. Rt'portcd valu es arc c~ average of th ~ ~asurt' mcn ts.
Sp ific arca of the v.vious types of carbon fiœ rs was dct cnn incd
b y nitrOj;t n (N>) BET ad sorpli on usmg an Aut osorb 1 MP from
Qwnt.l c hrom t Instrum ent s. Ad sorption isothtrms of nitrogr n
w c rc pcrformcd at n K.
M icro- tcnsile rcsril'lb was pcrformcd on mono- lîJ ammts of
To rayca• T700S and rtcyc ltd ca rbon fi be rs from pre pregs according to rundud ASTM 0 3379 and usi ng an ln stron Microtc-stcr
equ ipptd with a 2 N lrud cellA gage lt ngth of 10 mm was ustd.
Th e cJrbon fibc' rs werc- trstC'd ar a rat e of 1 mmjmin. Rcportcd VJIucs arc thr average of 30 samplcs for cach type of carbon fi ber.
3.2. Fabncarrm of rh ecorbonfib< r rm ifor ced
rrs composnes
AD mar criai s. including the- PPS rcsil\ wc re dr~ in an ovcn 'o
rcmo vc rcs idwl moisi\Jrc prior to m mpotmding. rrs and carbon
fibcrs wt' rc compoundcd using a LL-istritz 34 mm co-rotuing
tw in- scrcw exrru dcr comprts ing tcn mn cs. PPS ( in .1 powd cr rot e)
was ftrl JI the main hopper. whi~ urbon fi bers werc fc-d downst rœ m usiog a si& fœd cr. Th t' screw confi gurar ion w sclectNI
so .ts to minimi zc mc<h.ln tcal damage ro 1hc fi bers. and concillC'd
t hrcc zones ofmtxingclcrœ-n ts. The extruder was opcr.ucd ar a t otalthroughpur of 3 kgJh wi rh a scrcw spct d of t SO rprn Jnd a dit
temperature of 315 C. Th c cxtrudJtc was Ji r
led and pellet izt'd.
Sp irœm for mc-chanic.ll rcsring wcre molœd fro m t he- co mpos-
ites po li oiS usi ng a Boy 34 t injtcrion moldin g pross.l nj«rion tcrn pt'ra turc w.tS set bcrwc-cn 290 C and 30S • C. lnj ri on mold WJS
main ta incd al tlS "C to al low for crystall izari on of PPS. Cooling
timc was 40 s and cycle durarion was 55 s.
3.3. Oraromn:LIDal of th#: c:orbonjib<r rernforctd PI'S compos•er
The ttnsilc proponics of t he carbon Aber rcinforttd PPS compositrs we re mtJSurtd accord in g 10 su ntll rd ASTM 0638 usi n
a n In n m n 1123 machin< equip p..'<l wit h • 25 kN œil. TYP< 1 specimens w<rr t cSltd .r a crosshCJd spC<.'d or 5 mm(m in. An extmsomtt~r (50 mm. 101:) w.s ustd. Trnsi lr moduJus ( El m.»<imum
87
.,
llr r<>r< pyrol ysts
trnsar str s ( Gm ü ~ donaation a l brralc (Il>} and <n<rgy lo break
(E,} l't<r< lculllr d Values rr port <d Jr< lh< avrrag< or fivr mrarutt:"mcnrs forr h composia t'. The fractur-cd ccnsi k.- test s p..~mm s
wrrr ms pc rd usong a fir ld rrni ssion gun SEM Hitlchi S4700oprr.Jling at 2 kV to de termi ne the mode of fa1lurc and cvalw tc the
~hcsi on .t t thr fibcr{matn x intrrfacr. Polishcd swfa œs of untrstcd tcnsi lc rest sp imcns wcrc cx..:mlintd using a J 1 G 1
6100 SEM opcrallrlg at 10 kV ro dctrrrrUne fi ber oricnralion and
distribulion.
Fk'xuraJ propcrr~ s wcrC' t'valw tcd ac cording to standard ASTM
0790 usi ng an lnsiTon 1123 mJc hinr rquipptd wilh a 5 kN cd l.
l'l1c crosshcad spc<Cd was 13 mmJmi:n. The span wu 48 mm. Fkx·
ur al modulu s ( E1 ~ fl<xu ral yit ld strrss ( a,,). SI ra in a l yitld (r~, } and
cn t' rgy to yicld {Eh.) wcrc caJ cuJa tcd. Va hJCs rt!porred arr thC' average of fivc mrusurcmcnts for ca ch typC' of composite.
The imp.1ct C' ncrgy ( ~ was mcolSurcd usi ng the lzod un pa ct tcS1
(norch<d } acco rd ing oo su ndard ASTM 0256. Sp imrns hld J
thicknt5 S of 3.17 mm and a 2 lb-ll h.:unmcr was uscd. Values rc-por1cd are the avt' rag<" of 10 mcJsuremt"ftt s for c h composi te.
The thcnnal propcrtics of thr carbon fibcr reinforced compos·
Îtt'S WCr(' cv.lluafrd USIOg a differentiai SCJMing c.Jiorimctcr OS(
Q2
(TA ln srrumrniS} opcr.uin und<r niiT en. A hmling romp
rrom 25 C to 350 C al 20 (/ min was applitd. Ti'c mrkong
(a)
tempa-a ru rt' ( Tm ) an d th e inici.ll ayst aJ
at td . Th< crystal ro nt r nt was calculatrd
co nu~ n t
~H.
Yo = f
(z o) wrrc cvahJ·
rord ing to :
( 1)
· lill'.
wh cr< ll.H,. is ti'c t nt hllpy or rusion. M~ is lh < r nt hllpy of rusion
or 1
crystallinr I'PS and/ is thr r fftct iv< PI'S wogh l rrarrion in
œthe composi te. ln this v.ark. Y.c cmploycd t he valut' of ~\
port<d by Huo and Crbt 134 1(112 Jl g~
Finally. th r thrnnal stabilily of th< carbon rrinf"on:cd PI'S rompositt's wu eval ua cd using a lhcrmogravimctric analyzcr TGAJ
DSCt (Mr tt l<r Toledo ~ A i'cari ng r.~ m p was applitd rrom 25 "( 10
700 C a i 20 •CJ min und<r nil rogr n a ndair ann osphcres. Wr rc po n
tcmpa-aru rcs at 5 wt...X and tOwt .X dt'-gradar:ion ( Td. and r.u o). as
Wt' ll as t ht' mass of t he res id ut' at 700 OC.
4 . Res ultt
~nd
d iscussion
4.1. Ooaracnm::aoon of n-cydt'd carbon fib<'rs
'Or lcngth distribu tion of re<yclrd carbon fibr11 w.u cturactl'riz<d on a populaoon or 619 ondovidwl rccycltd fibtrs from
(b)
88
(a) 1 o
_ • - l cn}'Col l700S
,
.....;
00
t
''
'
1!0
70
i
GO
!
40
50
!
appcar.mœ of œcydrd camon fi> r " from prrpr s and from fin.
ishcd part s WJ.S rxarnincd by SEM . Th e œcydrd fi bors wrœ cl<an
and cxhibi tcd an .wc rage dia me ler of65 •Jm ( fig. 2 ~ The .tvcr.l gc
drnsi tyof t hr rrcyclcd ca rbon fibrrs fro m prr prr gs WJ.S 1.75 cm •.
Thi s va lut> is dose to t htorerica l dcn sity of vi rgin c arbon fibt-rs
( 1.8 g/c m'~ which furthrr confinns the good qu.•lity of th e rrclaimcd fibrrs. Specifie arca of th e fibers was dc tenn incd by N,
BET adsorption. Panrx 35 un sizrd virgin carbon fibrrs v.crt s hawn
to have a specifie arca of 1 m'/g and ta contJin nearly no porcs.
Rrcycl<d carbon fi>r" from prr prrgs and from fini shcd part s
ri ve ly 4 2 m 1Jg and
exhibit<d much high r r spt<:i fic aœas (res
1 8 m 'Jg ~ vmich migh t indica te a d eteriorati on o f the surfa œ of
the' Cilrlx>n fi bers du rio; t he pyrolys ls proccss..
Thr te nsil< propr rt ics of t hr rrcyclcd carbon fibcrs from prr prq;:s wcrr cvalw t«J using micro-- tcnsilr test in;. R«yclcd carbon
fibcrs arc re-c bin'K"d from a dive rse fC'Cdst oc.k bJW'd on variou s
types of carbon lïbe llO . Hr nce, thry arr aC! ually composcd of a mi x-
to-rcso nom propregsl
100
'
JO
so
100
:>oo
160
300
E(GPa)
(b) :~
to- rCF
noos)
11om pmpegsl
~
ig
~
(.)
1!0
70
compariso n purposcs. Th e rumull t ivc frequcncy di st ri>utions of
tc milc moduJu s and tc n silc strcngth ofTorayca• noos and r yc l<d c•rbon fibrrs from pœprcgs arr plo ttcd in fi g. 3. As r xp tcd.
rrcyclcd carbon fibcrs from prrprrgs show • broadcr distribution
in rc nsile moduJus and rcnsilc strcngth t lun Torayca • T700S fib c ~
Howcvcr. they rcuin ovrrall good propcrtics aflcr pyrol ysis. wi th
an average tcnsilc m odulus of 165 GPa and an average tcnsilc
st rength of 3415 MPa. Comparcd wi th TorJyca 0 17005 lïbr ~ this
rcprc.scnt s a diffcrC" ncc of - IOX in average rcnsilc modul us and
- 2~ in Jvcragc rm s ilc s trcngth.
_F
• - TCtiiiCil l100S
00
l
~
f
ture of difT-~ren t popu l.vions. For sake of simp lici ty. wc se lect cd a
for
singlr acro spaœ graœ ~ fr-rcnc c ma tcrial (To rJyc a...
/ .... • '
GO
so
40
JO
20
10
•1.2. Characu n;onon ofccrbon fi brr rr 111prctd PI'S romposaes
0
· 10
-+----,------,---,----r-- - -,
lOOO
000
4000
The pmpcrti cs of t ~ c arbon fib e r rcinforcrd rrs composit es
werr r v.lluatrd in rm sion. As cxp«tl'd , compositrs ronraining ca r·
bon fibcrs showcd cnhlnttd rc m~c propc-rrics comparcd 10 pure
PPS (Tablc 1 ~ Fo r a 40 Yll.X rrcydcd carbon fibrr content . th~ tmsi le modu lus was incrcascd by 6 80X.. t he ma ximum tcnsil t' srrcs s
by 680-7
the tlonsa rion at brtak by 20- 351t. and th< entrgy
to break (which is an indica t ion of tht toughnrss) by 9 10- llOO:t
Th~ tensilc propc n ics of the PPS composites made from rrcyct..-d
C.lrbOn fib e ts W€.TC sJ ightJy h.ighc r th.ll"' t hose nuœ from JlJOt'X
35 shon arbon fi bors. According to t hr tec hnicJI da tl of th e suppl~r. Pana 35 sho n arbon fitx-rs h.w c .1 tcmil t' modulus: o f
242 MPa and a trns üe st rength of 413 7 MPa. Ntoough it wJs not
possiblt' to w rify thos c valu rs by micro-- tcnsile 1 ting bcGluse
of the shon longth of Panox 35 fi bers (6 mm). it is unli ke ly that
5000
o_ (MPa)
1~1 Cu !T.ulltn.Y b-q U~:- rcvdnrn:.U c om o f ( J ) tt-m llt-rr...odu kn (.l) J nd (b )trnu k.:.t nw.xnr.um b:d (11-.-. ) for rcqd f'd c.ubon fi~N. from ~p rcp ( J.\'C'fJ~
<b - l b)W'.z::
m.u> - ).; :O MP.a ) J.nd \'1tpn a rbon fi hrn lorJ.yc-:.• 17
. ,~r~ : <f> · 182CP.o. :
- .OlB MPJ ).
m.
<:ttt"U
pr!'prcgs usi ng inugc an .Jiys is. ThC' average rngth was 5.6 mm
(standard d cvi.uion: 15 mm : 951t co nlidcn œ int< rval : 55 5.8 mm ~ Although not characrcrizr<l. r ydcd carbon fi bors from
fini sh.~
parts arr exp
cd to have a simiJar ~ngth distribu t ion
the samc proœss.. T ~ ph ysical
t he-y w crC" obclincd usin
b blrl
Tcn ~ ~ruMoff'P:) ~ ndcxbonfibt r ra rdc::l«e-d Pf") cort~liCUI!t e ( ~rroton m.N~m:-na cOfT'O.potlr::hrottr s ta nd .a'd d NU hOn; ..1 ntht v.-u horu·~prr nc-d ~ 1; wch teopf'Cl
:D :tr putr PPs rN tm). ~at ~ mak- m<d:.lb ~ r ~bo ç.-m f« ~ PPS C CifT1J<m: ~ tnriorcrd Wl:h nn"'drd c..tlon ftom prr-snp .n~ fuh::IOII ol fitrr cotten: ~ nd fibr-t
....,tb>n
~mforremrrw:
pf>
PP \GP..u'CX J.S
PP~rO ftom.p ~~
PP
ra from fin t'ha:! p.nJ
PP \0 P.a.rrx l
pf>
~
.Q()
rCI'!romp~
pp ra &o:n
fi n ~ cd
.10
.10
.10
pzu.
.Q()
.Q()
} ~ \'Cb.ae-Ji
Pl' •
.a !romp~
pf>
rCfbœop~
.10
( WU.)
( (CJ>•
J.9 tn.l:
14.7 tO..S
l h.Sto.l
1 7.4 tQ..S
l O.Stl. l
J O. . h t b
l O.ltO.J
tu. c,... ,~ •
1.U(X, • J}11)
J n..l(x. -1 )
1..1.8(x. - l p,
2l..1(l, .. .Hf
~U(Jt • l
' (<
~-..( M P~ )
2 4 tb
ln
,...
Hl
b&<
b!IO
6110
1071 J
11 11~
14 6.t 4
114 .12
2 1S
19 1 .11
.1 (1 )
..
"'
'99
61 8
7H
Q.97
...,,
'
,1( 1.
O.t.b 1 Q. l 8
O.a.& 1Q.Q}
Q..96t Q.Q.;
10.
l1
lO
.,
n.88.t 0.08
ll
0.89 1
.IS
21
0...90 1 0.02
r.ul
0 171Q.tlt
0 .94 tQ.OS
11 9 J. Q.1l
l .S .h Q. 18
1AS.t0...U
.l ( 'l)
~
9llS
2 .04.10.15
11 00
1..12 ttl l2
912
89
œ
(a)
(b)
(c)
1~···
obu..n·.:t'J3no!
I'Ù'Itd ~m o{PIJ~campamt-.s: (.1. ) 20 wt'L rf'C)ocltdcJrbon fibcn ftom p~
~l"' d r1 .ur .r;l ~1 !\beN prr.cnt an 1ht- crttr.po.t'l'l:t' w.1.1 ~ ); .:ud (c) ,.Owr 'L P.lnex U ..
(a)
.._~ S.
lhctu:Td :aarfo.et:S
of~ CDIT:pclme~
rt"'brud Wlth
40W'l.'1. mydtd
a.
flbt-rs!rom prrprrp (wtlu
(b)
rt'C')'dt'd
c.:rnon ntr rs from
p~~ (.: O wt.:t~: ( J. ) O\<en'1M"
.:t bor.-
~-n~flc_~con:
( b dtt.:.lh .:.1
~
rr~zficuon.
recydC'd crbon fibcrs h.Jvc ben cr inrrinsic tmsilt" propcrtics th.Jn
bcrwecnO and 1 dcpcndiog on tht- aspM
Pancx 35. Othor possi ble explarulions for the bellrr performance
rrs composi tes nudc from rccydcd carbon fibcrs rrügh t
be: ( i)difTcrences in dispersion andfordisDibution of t ho carb on fibers in tho matrix. and (ii ) ditfa-enc~ in adhosion JI th o PPSfca rbon fi ber i nlerfa œ .
As a first approximation. the longitudinal ~ensile modulus of
shon fi ber composi tt-s cao be cvalua tt'd using th~ foDowing ruJc
of mixtur<'. baSC'd on tho shoar- llg throty do""lopcd by Cox )35 J
for short fibcrs pcrfC'Ctly bondod lo tho matrix. and modifi!d by
Hull ID t>kc in t.o coontlho orientation of tho fi bers )36):
ttr di stancc bctween fi>cB. .vld
r.:stioof t ~
fibcrs and
of ttr
z, is a p.1rarœtcr compris cd be~
twccn 0 and 1 accou nr ing for the oriental ion of the fi bers (/. 1 - 1
ln t his eqwuon. E1 and
arc tho rcsp ti"" ~ensi!< moduli of
the fibcr and the m.1trix., Lt and a~....u e tht r pcctive volul'l'\C
fr.~cnon s of tho fi ·rand Ille maDix.z: is a par.~mrtor romprisC'd
for fi bers paralld t o Ille s tress dirc<tion. z 1 - 3/8 for in plane ran domly distributC'd fibcrs. 1.• - 1/ S for lhrC<'-dimensionaDy ran domly distribu tC'd fibers and 1. • - 0 for fibcrs pcrpcndicullr 1o
tho stress dirC'Ction l ln thi s study.lh<' followi~ para met ors W<>r<"
uSC'd: E1 -165GPa (Fig. H E,. - 3.9 GPa ( Ta ble 1) and b "' 1 duo
10 tho high aspca ratio of the fibors ( longth : 6 mm: diamele r:
651'm: possiblo,.Dition of tho fi bers du ring t ho ext rusion proc.-ss
is nol ronsiderC'd hor<' ~ Table 1 also gives tho throre tical t ensil.modulusof a PPS rompo site rcinforc!d willl rC"Cy<l!d camon fibe rs
from pœp~as a funa ion ofthcfiberrontrnt and of tho fibcrori ·
onl.ltion paramttcr z 1 • Tho rcsultssugg<-stlllatlho recydC'd carbon
fibcrs arc probably in-pllnodistributC'd and randomly ori roled. To
valida le lllis rMUI~ EM obS<rVations wa-e pcrfo""'...S on polish.....S
(2J
1
90
JO
lab.,. J
lfrlU.Ct propM"tiCS ol ~ ~d c_.hœ fibtr rsnbt:fd ~ m~t:e ( a"'«W on
m~.r.~ rrrru corre; ponds ta 1te- stand Id ~lOn :'' n th r vJ. N::I onnp-f':UI!'d en
l wr.h r~ ra the-ptXt- P~m.um
200
.
llt l
""'
...
~
UJ1
1J t O
PP:i.l\'0 P.ann l5
rO from JU"P"'P
~J r(T from ~mhed p.~ru
lO
lO
lO
PPS/\<f P.anu J5
~ ~ r(J from Jft'P!Tp
40
40
40
f'P:>/r<f from fimhed JlJ"-'
tt'fot h~
ff"flf tO tht
g ~cUrd dtvu.IIM
long1rudmal sortions of tho in lod sp imcn<. Th< microgro phs
lod u rbon fibo rs ar~ cssm rially atignod
conRrm !ha l 11>< r
al on,
th ~
in · rion dir«tion and
a~
cvm ly distributcd in the
mJ~
trix (Fig.•t ~ Tt'll" di spersion and dist nb ua ion arc very simi lar for rrs
composites reinforcrd with ranoc 35 shon ca rb on fi bers.
The fracturt"d surf: cs of thr ttrn-1lc trrt sp«i rncns wa-c obSOIVod by SEM. Cood adhesion was gcnorally obsorvrd al th e fi.
bcr/nu trix intrrfaœ dcspi tc the absence of any sizi ng on the
surfacr of rh< lib ers (Fig. s ~ Al lhoogh rho occu rronco or dobonding
JI fiborfma iTix inc ona co un bo obsorv«l faüure by tibor rupcuro
sc-ems to br the pr~mi ru n t 1'1'1C'Chlnism. This resu lt is con sis~n t
v,; t h th e increasc in elongation .11 brrakobsci"W'd for th e arbon fibor roi nfon:od compœi ros. si ncr GHbon fi bors tuvo a hlgh<r elo ngation at break tll.l n purr rrs.
rrs
finaUy. the trnsilc propcn ies of th e
composi tes rr info rt'cd
v,; t h rNydrd ca rbon fi bers wcrc co mp.Jrcd ro thosr of co nvne-ci.:JI
l'f'S compound< from RTP Company conuining 20 wU and
•10 l'A .% virgin c..-bon fibors 137 } Tho rosu~s. sunun..-i zod 111
Ag. 6. deMI y drmonsrr.u o th al sho n r<'cyclod c.ubon libers h.wo
lh r pOicnliaiiO compo lr with lh rir virgin equivalents.
fl oxu ral proporb os a~r ropo n od in Ta bi r 2. For a 40 wU r<'cy·
cled arbon fi ber conte nt . t he- fkoxural moc::hdus w.u tncr~ascd by
SJOX and rh r n oxur.~ l Slrrn a l yirld by 290- 310X com parod lo
pu re PPS. 0 pitr a dccroa<< of JOX in 11>< slrain JI y~rld. lh r ontf"~ 10 yirld is inarasod by 170-210X comparod lo pure rf' S. Conm ir nt wi th lho !l'nSIIr 1csri ng resui L<. Ih cfloxur.~l proponirsofth<
l'f'S composirrs mado from r<'cyCiod urbon fibors oxh1bi tod wC"o
round 10 bo high<r llun lhoso ITIJdo from ranox 3S s hon urbon fi.
bors. ln addirion. lhr products ITIJdo from r<'cyCiod carbon fibors
e<h1bt t simila r fl cxural propatÏC's to commercial compounds from
lh o RTl' Company bascd on virg111 ca rbon fi bors 1 37~
l .W. l
At-rual proptr.tn ol PP) .and a.rbcln fibtr r""fotcrd
rcop«t to tht puu Pfl) m.nn)
~ c om~n (~n'Of
P~ro J~
!{) (nwn p "1ftP
frotnfinnh«t p.ru
\Πh.nt1: .U
.a lnwn P"1ftP
t(J"
ra: from finn.htd p.:ru
10
lO
20
40
40
40
w
Ill
1!12
.....
l!.4
"''
!9 tl
t6 t1
l ...
l!.4
llod 1m~ œsistancr of the composi tes 11 rtportt<! m T ~Ir 3.
Tho l'f'S composi los con l .. nlllg r<'cyCiod urbo n fibC"s show mhancod proponus comparod lo pu ~r f'f'Sand lo composites mado
from Panox 3S shorl u rbon fi bor<. 11>r a •10 wU rrcydod c.Jrbon
fibor con le n ll h< impaCI rncrgy wa< inaruscd by 250Xcompared
10 purr l'l'S.
Th< c.ysldl cor< cr< or inJCC!od sa m pics or nca l l'f'S and PPS
composi l os ro111forcrd w1th rrcydod a rbon fibors from proprcgs
w.u cva lwtt"d by DSC. Tht" rcsul ts. sumnuru.t'd 1n Table 4. show
! lu i inj lion mo ld ing produ crs specimens having a degree o r
CI)'Stl llinity of abou t 38 VA.%. rega rdl ess of l h< carbon fib<r COn·
t c~ . Th cre fore, the incre.tsc 10 m«hanical prope r1 i
should be
mainly artTibu rrd to the pre5Cnœ of ca rbon fi bers and is not .tÇsoci.u C"d ro .1 ctunsc in ma tr riJI ayst.ll lini ry. Thr thLYm.JI srabib ty
was <VJIU.llod byTCA. ~suit< arc reporrod in Ta bl e 4. Tho lllCOIJ>e>rarion of rccyclcd arbon fi bers is not dcrrimcntal ro ~ ~ inhrrcnt
1h<rmal srabi lity or l'f'S and lh o onset or degradation ( T.,) r<mains
•pproxinu t <ly SIS C for aD sa mplrs. Furth orrnoro. l he pres mer of
re<.yciOO carbon fib:rs leach ro .v1 increuc of th e carbo ru CNMJs residu. ar 7
C which roachos 60-70 wU. This rrsul l i< or indusI rial intNcst si nec cturrins of polymcrs du ri ng 1he ir combu sti on
improvcs fi re retarda ney.
5. Conclusio ns
ln thls work. Cd rbon fibcrs wcrc rcdaimC"d by co mmcrci .ll sale
pyrolysis from carbon fibcr rcinforcrd 1hcrmosct composi tr v.astc
~en<rared by 11>< aC"ospacr indusl ry. Micro·Hnsilr lrsting and
dcnsi ty measuœmcnts showcd ttut the rr<Llimcd carbon fi bers rctaint'd SJ tisfactory propcrt ics. The rccycJOO carbon fibas wt>re
compoundcd wit h rrs to obtain compositrs containing 20wt .%
a nd4 0 w1.% r<'cydod c.J rbon fi bors. Th< lonsllr. ncxuraland impact
propcrnrs of the compos1 tts wcrt' cvalua tcd. k w~ danonstratl"d
1tu1 f'f'Scomposi!l's r<inforcod wi lh r<'cyCiod arbon fi bers rxhibi l
s1millr or bcttrr mc-charac.JI properrics than cqu1valcn t commercul compourds producrd using industrial ,rtldt' short v~r,in carbon fibcrs.. This confirms lhc hugc porrncial of crbon fibcrs
reclaimNi from ŒRP wastc to be incorpora red .1§ rcinforccmm ts
on mtJ1ln'md"':l corn:s.pon:b to
~~ ~.an:Urd ~'<Wl. t
u O'lf' VJM:aon
n:pr~\e'd 1n 'l .....,:-.
.
Q.l-1 t ODl
ll O.t1
1711
l JS t O..CU
l .AJ 1 O.O!J
lJ.
1t...l.t0.4
1b.9t.CU
J: .U tCU
1
0..14 t OD l
WH
1~
1A St O.Ol
147
lttO .t~
H9
117 t O.Ol
o..l4 .1 0D1
l b.t 1.0
l1.7t0.4
Jt0 t7
2!12
J 11
11 9t 0.04
l.l ltO.O:
"
OJ7 .t ODl
127
11J
2U
Rf'mfotœnv,. (Wt \ )
\()
.t ( 'l.
"'"
J7! l
.li t j
50
ltc,. ' · ltntllf' pttlfl dtW" ' al m cotn.J'O!olln trmbrc~wlth
Wodc.a.rbon fiht-n
.,d œtnnkttul ~ com.p!'!Urd' rt'tnbrcf'd w11h 'bx"f ,,L'Jl" u.
fiht-n I J 7~
W'ijl m )
1
S34
m ..
1(< )
l(y( 't)
1( < )
1 .1 4 t (U4
110
r,, Ol
1("(,
Q. 1S t OD4
.l.l
.l2
11>
0.41 t 0.02
0.47 .t OD l
1l7
91
71
l .J.hlr-4
n'NI ptOPer:IM el PP:.
J. ~ PP.)
)<dtd arbon fi, cn from prcpc-p f,n
con..,tt".co rt'1nbrœd .......:h
~ crm lne'd
by 0
,,.•re
lM
~1 2
...
!. 19
sn
~ lb
1'19
279
~, .
"'
S29
"'
• trror on C"\"StJI cor~ r- n11s1 1l.
' l.tTOr cm tcm.pc-r-* Urt r1 t. l "'L
~ k d du c- n «"VJ. •tt"d J.l
~ . f.JTOt on rer: du c- n tb
in ncvt composi l
Such m_. cri als might br- u ~ for swta ble
applica t ions ci thcr 10 the acros pare i nd ~ ry or in he r m.u krts..
j 17f <...M .a.J J Y. WC".slev
\t P'fl«h et.nr
1111 Adhcn·nr
n.
t\"d ML
T«hnolog'lr:'
~c-p.:tt'd
lnc
CPrnpoatt> t«\'Cbrtg proo::r-u 1,..
<Nrp- v.~
he-r~l'll
l'rlobprl• J\"''Q rd ~D.:..IlJ
c:4..n ritro n<D\
l7\t J. n..acta:rd bcd proc:r-u.
(Dfrl)ODie-.1 ~
zn. M.rch. 1
. p.9
trd'\ cnmJ
t«\'Chn ~
11~ J Kr- mrrlv ,Jk.
Acknowh.'d !:"m <nts
This proj 1 ( oclc n ri~ cd J.S CRIAQ ENV-411 proJ 1) wu su J)portai by th e- Consort iu m for Rc~.uch and lnnov.1tion in Aao.
spa cc on Qucb
(C RJIIQ ~ Bd l Hcticopc e< TcxiTon û nJdJ lld
(Mira bd. Que
. (J nada ) and Bomb.lrdic r Ac rospacc (MontrcJ I,
Que
Can> d a).
Re-fere-na'$
fll
~ cn:.tAl
n-.c r- O.~t. t.btul nur k:nappontmii~~Mforc:rbonfibC'n: J.n
n~hr:t l")' n'Oh"ln~ mo ~h \ '01\Hr.t" procr-u~ ln : CDmp&QfN world arbon
121
b r 20 11 conlrrc-rce
Oea~r ~
7.
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• 2011
P'urA"tC.: !t.. PmM ~1 ii.C"C\'C bn ~ czbon ~rr re nforcrd polyrrrn br UNCtuu l
t»n': whno ;::v tn'Y'W .::ld rr..:: C'l ou d
•t.u R- M.:n.:.~
:D11 ~ 1 ! ,:J7M ~
Rrpll .z10n R:e:;peoa mg the- 01~ PJ.y.Z, k b: t hr' On:pM.:I of ii.Nldwl
M:t c- N-k <t.tp:J IWWWCin hl~l tnlq<r ~ ~ '!r~ r rrq cq l r .OIJ -* C'U i rTq
~ pb
Ill
cq l r J.h er. l>- JvmcC"d 1Q.1l 1 1J
J.:J t.:.ndfiD
1 ~1
lbl
f7J
Dlr~~n~~ on W.z.s~r (1999,CJ1JlC <tctp: ec.neop.uuit-nVII"'O"'rrrnr,;
Yn1tC'!\.t_ndfiQ...mdt'x.Nrn• J\"HII ed mD711J.
&d
lz{f'
Vdudr
DlrtdnT
( 20 1.11[(
m\'U'Onrr.mti'W~ItiC'!v_mdC' hur.,. I\"''Qk'd ..._07 11 1
<h tr;J ;fl«
C"'UU"'p~f'"u
Prlm '1' ~J V«yê~ tt<hnool~ br lhmr..o-..e-t cnrrpo-.:ztf'" nutmJ. k
c:urra'lt ~.:.t\1'1.. <.om.poutC""'' P.:.n A lO ..;J1\8 ~ I lOt. 1 ~
~ 'ltdubw.J 1. Olu.no Y. lJ.~.J. l M«l'u.nlC~ pro pt-n'W'' o( NI ~ rn:~n
re n!orœd "M c:! rrn'Citod (fltp Advzac:rd lorr.pou ~ M.:~n.z.k · ThC' ()(h::u.l
f&J ~J.~~~~h~~;$UUN.~=t 1, r_.;~c-·~~~~l: _t.;:~~~ ..~
~r~=~~~r~'tJ.
ct :.l
'CtC"dO"Io:Pbv111«nonrr.o!dm nY thod..K.t. M lnl
.:r_
191 P.:lm J <.hau. OR. ~vJ.gt 1... f.\'J.M
Succrufu l cbud loop rrnodlf\; or
c:~c- nro~t com
r ' Comp<mtc-1 P.:n A 20 , :0,.4):
..&.
II OJ ( uberrv W AupYne ft'C)odmg c-fb re bt-nrfir Bœmgopc~n t~ ~m~AIJt.O
,\ b.ptrn:- QlCl '-.Œ.
• p.b 1J
j11J U'\h\:oûu K. ~orr..liS\1 N.. \~o M. V«\•dlng cl OW ~· pyrotv~u rr.tl:lod.
M:I C!" So tpn 1 ~;~ .:99~-'28 .U .
l..urvoj
jt lj bi!J.Jl lr-.rc:vn ~ Ultb:::uon o!-.ctJ.pthc-~u uun~ P\'f'Otvst:l. f'"IY~
1ourcN P.:n A:. WraJ\"t'rv UnJ [:1\.,ron urcu 2 ~11 (1 ~ 7f. .r,
ji J) ADen Rf_ (h.:rJ.Ctr:n: .;ttonol r«Uur.C'd czbon fibrrs J.nd C'lru m~;uhon t N D
ntw lhf'rmcl'".rt
\"'11'4
mot ncc: YU tXN"t~ ctHrpct$1~ fJ.bnc .S tOn
tt<h,_que-, lib)r h ' 'bre"l CzobnJ. Sc. tc- UmTr-.;aty ; ..!!llN 1.!8 p.
1141 O.(. c.:rbon rttr l td. <httP'" I/Woww ~ledcJ.
fi)rc.com,.
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oll
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nd RI': . lhnw
LA tc-ntJ.rv rrc\'C" bn
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,U (2~!U
101
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~mrrr1 ~·JK,. Kdtvii.M,ftnwtd:t-.1 Plchrm ~J il.txid lO. Th:-di.J.-r
c-n.-uhon
J.nd tt'lH~ of p.nt fitns rr<yrlt:d from 'ICJ"~ CD
~ bo.• tb: .J.Cton el J.fkudtwd
proctu.. (om pMIIc:; P.:n A 1 S; 1 ):KJ9 •
1.n 1 PieU~ ~,L. ~t R\l cn ~rirv JR il.~d <D. fC'rrwd: "1 A fkudl'lof'd b«i
prcxr-u for l:h t> t«O\Tt\' al gl:lu fin~ from -re r~ C\tm\O'".C"t compoutMCo""l'OC 1 Tf'd'lnorl
0: .; ~
ll
fllf Jl.lns C... Pk"k:C'nn~ ~J tt, ~ , C. Hklod P. W.nuw N. Rf'<)'hnt;c.J n tèrrirpo-.:v
IC.
IN ÛWI((ornpM M.:tC"r
n-un mcr.poutt'".l: uvng ~C'rc'll lC J. I propJ.
7
(.U 1P\n ~ro llrm.J~ K. C....:ro.J )t-rN J. ()r(:dch C.. )hodr J Pob.J.b:llf .
M.J.
~ ~ .1 l Ole-mel rf'C\<dtng of urbon fi) rf' COfrJ'CI1ftC'l ~nt: J.kn
U!"ldt'r
wbo:ntol :.rd o;upr-l'tTi c al (l)l'ldl c orn. J ~rm t rlu:<h
;.; 1):31 !.
f.l4 f 8J1 Y. WJ. - l , rf'"~ L C. l"rm.:.:l t"t'C.)'Clm ~ o! c.:.nxm fi be-N rr tnbrcrd C""pOXV
ft'"M comp:r.;lte m OXV::f'"n 1n .~C'1'C'IttC".: I wlt-t
~tue-r
De
.!O I O;J I 2):gr_6 1 2
~~~ ~l'lt.6ht (.(. Un ( , lhZig: (. \VJ.~ B. litn")'C bn ~ ol WO'\""<"ft Ottlon fib«ff'"mfon:cd
\"'11'4 composttC't US if'lè 1 up
nttC".J I WJ. If'f l.fT\'rf011 Tf"àànr:tl
J.tO)
I!Oll; J..(b ;:W9
-4:
f;,t,l
FYkC'nflë ~ L. turner lA VJ.rno~ W... Mouktms compound d ~T b prr>t"l'll u~.;
tt<\'Cit:d crton ftx-N tnt
MPl 1Kh (onfl
;t.7 :1Cl.
1211 Tumrr lA. Ptcktnns ~.J.. Vhmor NA. Dc-\Tklpmti'C ot h h , .J. corr:puar
n:•t-1Ul \tm~ f«\'C"!Nt crlonfibrr-ln: l ntc-m:uorul
\C P{~)-:rtpMaa.. J,_nd
(xhtbcton(Pro~p ). \'Dl~4.. 2
p . IQ.
flXI WCI!r\; KH. Pdz:nn' SJ. Tu rn!:T l A.. W...-n or SA. t. o:r.prn.-J.on rr..ouldt~ o4.:
r«)'C"Rd arbon fi)rr ~mbrcC"d rpœry com.poDit tn : ln ~ mJ..co:u.l
~[
~ympMun :t'Id l".xhl~10n ( Procnd snp.). ''01.. ~
9.. p. 12.
!..SI MdültvT . B~-d P..
orv(. 8JC"n0 Moore- l Mtllar B. Cf .1 l k«)'C k<!c.J~
fibt-rfiiJt.d
\'rC"t vlrnt-mmpœxM.JApp l f'otvm ~a.l
; 107 ( l ) :.sl 1 ~ 1. 1
1101 l.unrwb 1
~ pq; M. VJ.mJ. J M~dunac.al pt rlonr..:rc ~ o! J. I"K)'ded
arbon fin- IPP mmpo-.:ztc-. r.xp Mf"<h 20 11 :~ t (• ~~7 17
IJt J Aloon:b M U, ~tf'rl:"C' (A f'".: tt BM. 1?«\drd C.Jrbon ti br~ rt"trdorc-cd
)11'0Pvkrr
thcm--094.U te
Com.petn iN
f'..:.n
A
ltll l;4l( 1): 79 .....
I.UJ
\V'~KH. S)'t'd ·
.nrr.C"dO , Pid:ttm~"f . B
ii.. L!"«"tolc~hn_;~ne
on ranfomrç; p<*:ntulol rt<)'(led C.Jrbon fi)rr bt p 'Ptof'\'lrnf'" CDmpQQ(t.
(D~
tltd'i
1!01l;74,7)~ ill 4;
IJJI (..J.w K. C C"CJ~i't' P u ~ cl rt'<'\<Ck<! .lt-rt~q~œ- p-uic- arbOn fi bt-n; m
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(-«<<o:p 2010
ll4 1 ~oP . Ct-t:Jr P. f. ft'ec-u ol the-..-nu l hr2orv on l:lt npd .JmatphCM ph.:.·.r L"'
pht:ny\rnr llll~t , (ollcud ~ Sc1 1 !6.!:l
9): ~ ~l..
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App l Ph~ 1 ~ 2-.1 :7! 9
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Prr:n: 1 ~ 1
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