POLYMER COMPOSITE MATERIALS BASED ON COCONUT FIBRES SUBTITLE OF THE PHD Le Quan Ngoc TRAN Members of the Examination Committee: Prof Paul Sas, Chair Prof Ignace Verpoest, Promoter Dr Aart Willem Van Vuure, Promoter Prof Christine Dupont-Gillain Prof Jin Won Seo Prof Bart Blanpain Prof Peter Van Puyvelde Prof Stepan Lomov Dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Engineering December 2012 © 2009 Katholieke Universiteit Leuven, Groep Wetenschap & Technologie, Arenberg Doctoraatsschool, W de Croylaan 6, 3001 Heverlee, België Alle rechten voorbehouden Niets uit deze uitgave mag worden vermenigvuldigd en/of openbaar gemaakt worden door middel van druk, fotokopie, microfilm, elektronisch of op welke andere wijze ook zonder voorafgaandelijke schriftelijke toestemming van de uitgever All rights reserved No part of the publication may be reproduced in any form by print, photoprint, microfilm, electronic or any other means without written permission from the publisher ISBN 978-94-6018-615-8 D/2013/7515/3 Cover image: SEM image of fracture surface of coir epoxy composite, showing defibrillation of the coir fibres i Acknowledgements My career in composite materials started from a great occasion when I met Prof Ignace Verpoest in Vietnam in 2001 He opened a wide door for me to enter into the interesting field of composite materials by receiving me into the Master program EUPOCO Since that time, I have learned from him not only valuable knowledge and experience but also his kindness in supporting people In the past four years of my PhD, as my promoter, Prof Ignace Verpoest has provided me patient guidance, enthusiastic encouragement and useful inputs for this research work I would like to take this opportunity to express my deepest gratitude to him for all his supports I would like to express my great appreciation to my co-promoter Dr Aart W Van Vuure for his knowledge, advice and available time for guiding me Working in the natural fibre composites group, I enjoy very much both his leadership and friendship I also thank for his patience in correcting my papers and the first draft of this dissertation I would like to offer my special thanks to Prof Christine Dupont-Gillain for her kind help in building up the method for wetting measurement of natural fibres, and giving useful comments and inputs for papers and the thesis manuscript My grateful thanks are extended to Prof Stepan Lomov, Prof Bart Blanpain and Prof Peter Van Puyvelde, as members of advisory committee and examination committee, for their advice on my research, reading and providing valuable remarks for the manuscript I would like to thank other members of the jury, Prof Jin Won Seo, for her effort to read my thesis and evaluate my work and Prof Paul Sas for being the chairman of my thesis defense The four years research consisting of many experiments and testing would have never been successful without the technical assistance of Kris Van de Staey, Bart Pelgrims, Manuël Adams, Danny Winant, Sylvie Derclaye, Yasmine Adriaensen and Michel Genet I greatly appreciate their help Additional thanks to Gregory Pyka for his training on using SEM-CT I would also like to thank Aniko Lantos, Huberte Cloosen and other MTM secretaries for their kind help in important administrative work ii My warmest thanks to CMG friends who are always willing to offer me their help, especially, my officemates Carlos Fuentes, Lina Osorio, Eduardo Trujillo, Ichiro Taketa and Yasmine Mosleh for sharing nice time (in and out the office) during these years The thesis work of Linde De Vriese, Elisa Melcon Miguel, Delphine Depuydt and Laurena Van Oproy is contributed to this work They have had high motivation in working with coir fibre composites, and obtained good initial results which help to have further studies in this thesis Thank you very much My acknowledgements are addressed to KU Leuven for providing I.R.O Scholarships and Belgian Science Policy Department (BelSPO) for supporting our research I also wish to thank the staff involved in the BelSPO-MOST project Prof Bui Chuong, Dr Truong Chi Thanh for their advice and providing the fibres for the research My family and I would have never had such a nice life in Leuven without the care and support of Belgian and Vietnamese friends I am really thankful to Mr Jo Mariën and his wife Claire Mariën Con cảm ơn Chú Thiếm Kim nhiều quan tâm giúp đỡ gia đình suốt thời gian Bỉ Cám ơn chiến hữu Cần Thơ giúp đỡ chia sẻ vui buồn lúc xa quê Finally, I want to express my deepest thank to my parents for their support and encouragement throughout the years My special thanks go to my wife Loan and my little daughter Au Lam who was born in Leuven, for their love and support They are the driving force in my life This thesis is dedicated to them iii Abstract The interest in using natural fibres in composite materials has greatly increased over the past decades thanks to their good mechanical properties in combination with environment-friendly characteristics In this research, Vietnamese coir fibres are studied and modified for use in composite materials To be efficiently used in composite materials, the microstructure and the mechanical properties of coir fibres are first characterised Secondly, the surface of natural fibres has a complex morphology with chemical heterogeneity and relatively high roughness, which strongly influences the fibre-matrix interfacial adhesion Therefore, it is important to acquire a systematic understanding of the fibre-matrix interfacial interactions in composites Lastly, unidirectional (UD) composites of coir fibre in both thermoplastic and thermoset matrices are examined to evaluate the possible value of coir fibre for composites The microstructure of technical coir fibres is examined using SEM and SEM-CT The results show that technical coir fibres comprise plenty of elementary fibres and a lacuna at the centre The elementary fibre is built up by two main cell walls which consist of bundles of microfibrils aligned in a high angle to the fibre axis Coir fibre appears to have high porosity at 22 to 30% The mechanical properties of coir fibre are determined in tensile tests including single fibre tensile testing with optical strain mapping and single fibre tensile testing using different test lengths The results of both methods indicate that coir fibres are not very strong and stiff, but have high strain to failure An integrated physical-chemical-micromechanical approach is implemented to investigate the fibre-matrix interfacial compatibility and adhesion of the coir fibre composites In this study, the interface between untreated and alkali treated coir fibres and various thermoplastics is characterised The differences of fibre surface chemistry and properties of the matrices in terms of surface energy and potential chemical reactions are considered Wetting measurements of the fibres and the matrices are carried out to obtain their static equilibrium contact angles in various liquids, and these are used to estimate the surface energies comprising of different components The work of adhesion is calculated for each composite system, accordingly Also, fibre surface chemistry is examined by X-ray photoelectron spectroscopy (XPS) to have more information about functional groups at the fibre surface, which assists in a deeper understanding of the interactions at the composite interfaces To determine the quality of the composite interfaces, single fibre pull-out tests and transverse three point bending tests are performed on UD composites to iv measure interfacial shear strength and interfacial strength (mode I) respectively The results suggest that the higher interfacial adhesion of coir fibres with polyvinylidene fluoride compared with polypropylene can be attributed to higher fibre-matrix physico-chemical interaction corresponding with the work of adhesion Whilst the improvement of interfacial adhesion for coir fibres with maleic anhydride grafted polypropylene compared with polypropylene can probably be attributed to a chemical adhesion mechanism In addition to the specific results for coir fibre composites, the integrated physical-chemical-micromechanical approach to investigate and improve fibre-matrix interface has been developed This knowledge can be applied to study the interface of other natural fibre composite systems Mechanical properties of UD coir fibre composites with both thermoplastic and thermoset matrices are assessed by tensile tests in fibre direction, flexural tests and unnotched Izod impact tests In agreement with the interface evaluation, higher flexural strength and stiffness are found in the alkali treated fibre composites, probably thanks to the better interfacial adhesion The impact strength of coir polypropylene composite is not significantly different from that of neat polymer, while the coir fibres can improve the toughness of epoxy by minimum a factor of three, when the impact strength is considered as toughness indicator An initial study on coir-bamboo fibre hybrid composites is carried out to investigate the hybrid effect of tough coir fibre and brittle bamboo fibre in composites With a low bamboo fibre fraction, a hybrid effect with an increase of composite strain to failure is obtained, which can be attributed to the high strain to failure of the coir fibres Meanwhile, the bamboo fibres provide high stiffness and strength to the composites The results show a potential for coir-bamboo hybrid composites, which justifies further study on this topic v Samenvatting In de afgelopen decennia is de interesse in het gebruik van natuurlijke vezels voor gebruik in composietmaterialen sterk toegenomen, vanwege hun goede mechanische eigenschappen in combinatie met mileuvriendelijke karakteristieken In dit onderzoek worden Vietnamese cocosvezels onderzocht en gemodificeerd voor gebruik in composietmaterialen Om een efficiënt gebruik van de vezels toe te laten in composietmaterialen, worden eerst de microstructuur en de mechanische eigenschappen van de cocosvezels gekarakteriseerd In de tweede plaats heeft het oppervlak van natuurvezels een complexe morfologie met chemische heterogeniteit en een relatief grote ruwheid Deze factoren beïnvloeden sterk de vezel-matrix interfase adhesie Daarom is het belangrijk om een systematisch begrip te verwerven van de vezel-matrix interfase interacties in composieten Tenslotte worden unidirectionele (UD) composieten van cocosvezel in zowel thermoplastische als thermohardende matrices onderzocht, om een beoordeling te maken van de mogelijke waarde van cocosvezels voor gebruik in composieten De microstructuur van technische cocosvezels is onderzocht met SEM en SEM-CT De resultaten laten zien dat de technische cocosvezels bestaan uit een reeks van elementaire vezels met een lacuna in het centrum De elementaire vezels zijn voornamelijk opgebouwd uit twee celwanden die bestaan uit bundels van microfibrillen die een grote hoek maken met de vezelas Cocosvezels blijken een hoge porositeit te hebben van 22 tot 30% De mechanische eigenschappen van cocosvezel worden bepaald met behulp van trekproeven, zowel met trekproeven op enkelvoudige technische vezels met behulp van optische rekmetingen, als met trekproeven op technische vezels met een reeks van testlengtes De resultaten van beide methoden geven aan dat cocosvezels niet zozeer sterk en stijf zijn, maar wel een hoge breukrek hebben Een geïntegreerde fysisch-chemische-micromechanische aanpak werd gebruikt om de vezel-matrix compatibiliteit en adhesie te onderzoeken in cocosvezel composieten In deze studie werd de interfase gekarakteriseerd van zowel onbehandelde als met alkali behandelde cocosvezels in een reeks van thermoplastische matrices Verschillen in oppervlaktechemie van de vezels en eigenschappen van de matrices in termen van oppervlakte-energie en mogelijke chemische reacties werden beschouwd Bevochtigings experimenten van de vezels en de matrices werden uitgevoerd om hun statische evenwichts contacthoeken te bepalen in verscheidene vloeistoffen Met deze contacthoeken werden de oppervlakte-energieën en de verschillende componenten hiervan bepaald, voor vi zowel vezels als matrices Vervolgens wordt hiermee de theoretische adhesie arbeid bepaald voor elk composiet systeem Verder wordt de oppervlakte-chemie van de vezels bepaald met behulp van Röntgen fotoelectron spectroscopy (XPS), om meer informatie te verkrijgen over functionele groepen aan het vezeloppervlak Hiermee kunnen interacties in de composiet interfase beter begrepen worden Om de kwaliteit van de composiet interfase te bepalen worden pull-out testen uitgevoerd op enkelvoudige technische vezels, alsmede transversale buigproeven uitgevoerd op unidirectionele composieten Dit om respectievelijk de afschuifsterkte van het grensvlak te bepalen en de mode I interfase sterkte De resultaten suggereren dat de hogere interfase sterkte van cocosvezel met polyvinylidene fluoride vergeleken met polypropyleen kunnen worden toegeschreven aan sterkere vezelmatrix fysisch-chemische interactie, in overeenstemming met de theoretische adhesie-energie Tegelijkertijd wordt de verbetering in interfase adhesie voor cocosvezel met maleinezuur anhydride gemodificeerde polypropeen toegeschreven aan een chemisch adhesie mechanisme Naast specifieke resultaten voor cocosvezel composieten, werd in deze studie de geïntegreerde fysisch-chemische-micromechanische aanpak ontwikkeld om de vezel-matrix interfase te onderzoeken en te verbeteren Deze kennis kan gebruikt worden om de interfase te onderzoeken in andere (natuurvezel) composieten De mechanische eigenschappen van unidirectionele cocosvezel composieten met zowel thermoplastische als thermohardende matrix werden onderzocht door trekproeven in vezelrichting, buigtesten en Izod impacttesten zonder kerf In overeenstemming met de interfase evaluatie, worden hogere buigsterkte en stijfheid gevonden in alkali behandelde composieten, waarschijnlijk door betere interfase adhesie De impactsterkte van cocosvezel polypropeen composiet is niet significant verschillend van die van onversterkte polypropeen, terwijl cocosvezel de taaiheid van epoxy kan verbeteren met minimaal een factor drie (indien impactsterkte wordt gebruikt als indicator van taaiheid) Een initiële studie werd uitgevoerd op cocosvezel-bamboevezel hybride composieten, om het hybride effect te onderzoeken in composiet van taaie cocosvezels en sterke maar brosse bamboevezels Met een lage bamboevezel fractie wordt een positief hybride effect gevonden voor de composiet breukrek, wat kan worden toegeschreven aan de hoge breukrek van de cocosvezels Tegelijkertijd geven de bamboevezels hoge stijfheid en sterkte aan de composieten De resultaten vii laten het potentieel zien van cocos-bamboe hybride composieten, wat een verdere studie van dit onderwerp ondersteunt viii Chapter 164 The impact properties of the UD composites were studied in two systems, namely coir/PP and coir/epoxy The result for the Izod impact strength showed that the toughness of PP cannot be improved by adding coir fibres; while, for the brittle epoxy, coir fibres can improve the toughness with minimum a factor of five The effects of fibre loading and fibre treatment on the composite impact strength were also investigated for the coir/epoxy composites The results showed an optimum value of fibre loading to obtain highest impact strength Above this value, the impact strength decreased The fibre treatment improved the composite interface, which then also improved the composite impact strength An initial study on coir-bamboo fibre hybrid composites in PP was conducted With a low bamboo fibre fraction, a hybrid effect with an increase of composite strain to failure was obtained, which can be attributed to the high strain to failure of the coir fibres; the bamboo fibres provided high stiffness and strength to the composites The results show a potential for coir-bamboo hybrid composites, which justifies further study References Osorio, L., et al., Morphological aspects and mechanical properties of single bamboo fibers and flexural characterization of bamboo/epoxy composites Journal of Reinforced Plastics and Composites, 2011 30(5): p 396-408 Truong, T.C., The mechanical performance and damage of multiaxial multi-ply carbon fabric reinforced composites, in Department of metallurgy and applied materials science, Faculty of engineering sciences 2005, Katholieke Universiteit Leuven Swolfs, Y., L Gorbatikh, and I Verpoest, A 3D finite element analysis of static stress concentrations around a broken fibre, in 15th European Conference on Composite Materials (ECCM) 2012: Venice, Italy Swolfs, Y., et al., Interlayer hybridization of unidirectional glass fibre composites with self-reinforced polypropylene, in 15th European Conference on Composite Materials (ECCM) 2012: Venice, Italy Taketa, I., Analysis of failure machanisms and hybrid effects in carbon fibre reinforced thermoplastic composites 2011, Katholieke Universiteit Leuven: Leuven, Belgium Tran, L.Q.N., et al., Investigating the interfacial compatibility and adhesion of coir fibre composites ICCM 18 proceeding, Korea 2011 Cichocki Jr, F and J Thomason, Thermoelastic anisotropy of a natural fiber Composites Science and Technology, 2002 62(5): p 669-678 Vander Velpen, H., Characterization of discontinuous UD bamboo fibre composites in Department MTM 2010, Katholieke Universiteit Leuven Conclusions 165 Chapter Conclusions 166 Chapter 6.1 General conclusions This doctoral thesis has presented a study on the structure and properties of natural coir fibres, the mechanical properties of their composites, and especially the interfacial interaction between the natural fibre and polymers which is significantly important for using natural fibres in composite materials The result of the research has largely followed the study plan and achieved the thesis objectives As commonly accepted, the consideration for using natural fibres in composites is based on a few main aspects: their favourable specific properties for composite applications, economy, ecology, and society Following these considerations, coir fibres were shown as a suitable candidate; these are tough fibres and potentially can perform as toughening reinforcement for brittle polymer composites They can be considered as cheap fibres for composites and are available in large amounts For a developing country like Vietnam, which has its own coir fibre production, the use of coir fibre in composites will indirectly contribute to improving the low income of local workers who are directly producing the fibres The most important contribution of this thesis is a developed procedure for studying the interface of natural coir fibre composites An integrated physical-chemicalmicromechanical approach to improve fibre-matrix interfacial compatibility and adhesion was implemented This knowledge can be applied in not only coir fibre composites but also for other (natural) fibres used in composite materials It can be used to optimise the interface properties through fibre treatments and matrix modifications In addition to above major results, the conclusions of this thesis are summarised in terms of output, as follows: 6.1.1 Microstructure and mechanical properties of technical coir fibres The internal structure of technical coir fibres was characterised using SEM and SEM-CT The result shows a technical coir fibre comprises plenty of elementary fibres with the lumens inside, and a lacuna at the centre of the fibre As a result, coir fibre appears to have high porosity at approximately 30% The elementary fibre is built up by two main cell walls which consist of bundles of microfibrils aligned in a high angle to the fibre axis (around 45 degrees in the primary wall, and close to 90 degrees in the secondary wall) Concerning the characterisation technique, SEM-CT is a good tool for analysing the internal structure of coir fibre The fibre porosity and Conclusions 167 the dimensions of lumen, lacuna and elementary fibres were determined by using a 3D model of the scanned fibre This technique can also be applied for characterisation of other natural fibres The surface of coir fibre was observed by SEM and there are arrays of silicon rich protrusions, which can possibly be removed by mechanical or chemical treatment of the fibre surface Furthermore the fibre surface consists of longitudinally oriented cells with more or less parallel orientation; it is suggested in literature that these cells are firmly held together by a binder of lignin and fatty substances which are filling the intercellular space This is confirmed in this study by the analysis of fibre surface chemistry using XPS, in which XPS indicates a heterogeneous surface with a high proportion of hydrocarbon rich material consisting of waxes, fatty substances and lignin Moreover, on fibre treatment with alkali, the waxes are largely removed and leave a relatively homogenous surface with more exposed lignin as binder of elementary fibres The characterisation of the coir fibre surface provides useful information which will help to improve or modify the fibre-matrix interfacial adhesion when the fibres are used in composites The mechanical properties of the coir fibres were assessed by single fibre tensile testing, in which the fibre strain was determined by two methods: with optical strain mapping and using different test lengths The results of both methods indicate that coir fibres are not very strong and stiff, but have high strain to failure This is explained by the high microfibrillar angle in the fibres leading to the low stiffness in fibre direction and to high elongation thanks to reorientation of the microfibrils under tensile loading 6.1.2 Wetting measurements and surface energy estimation of the fibres A wetting measurement procedure was established to determine stable and reproducible static contact angles of coir fibres, in which the effects on the contact angle results of irregular wetted length along the fibre perimeter and liquid absorption were carefully considered Regarding this, the dynamic contact angles of coir fibre were determined following the Wilhelmy method Using the Molecularkinetic theory, the wetting behaviour of coir fibre is also modelled by fitting the dynamic advancing contact angles corresponding to different measurement speeds, which also provides the static contact angle The values of the static angles were further used to estimate fibre surface energy 168 Chapter The surface energy of coir fibres was estimated following two approaches, namely the geometric-mean approach and the acid-base approach, which describe the fibre surface energy comprising on the one hand polar and dispersive components and on the other hand a Lifshitz – van de Waals component and acid-base components Both approaches suggest the coir fibre surface has high dispersive and low polar contributions, which points to a surface with rather hydrophobic properties This result is also in agreement with the analysis of fibre surface chemistry by XPS 6.1.3 Fibre-matrix interfacial compatibility and adhesion Wetting analysis provides the surface energies of the coir fibres and various matrices, which are used to calculate the fibre-matrix work of adhesion and interfacial energy to predict the physical adhesion and compatibility of the composites Next, practical adhesion in single fibre composites and UD composites was evaluated using single fibre pull-out tests and transverse three-point bending tests In this work, untreated and alkali treated coir fibres and various thermoplastics were investigated From the wetting analysis, the results show that the work of adhesion of both untreated and treated fibres with PVDF is higher than in case of PP and MAPP On the other hand, the results of pull-out and transverse 3PB tests show much higher interfacial adhesion of coir fibres with both PVDF and MAPP in comparison with PP This suggests that the higher interfacial adhesion of coir fibres with PVDF compared with PP is thanks to higher fibre-matrix physico-chemical interaction corresponding with the work of adhesion, while the improvement of interfacial adhesion between coir fibres and MAPP versus coir fibres and PP is likely dominated by chemical bonding There has been a good agreement between the results of the wetting analysis and those of the composite interface mechanical tests The combination of different characterisation techniques has offered a deeper understanding of the interfacial adhesion and compatibility in coir fibre composites 6.1.4 Performance of coir fibre composites Mechanical properties of UD untreated and alkali treated coir fibre composites in both thermoplastic and thermoset matrices were assessed by flexural tests, tensile test and unnotched Izod impact tests Conclusions 169 The results from flexural testing show that the coir fibre composites with PVDF and epoxy are stronger and stiffer compared to the coir fibre PP and MAPP composites The transverse strength of the composites indicates a low interfacial adhesion of coir/PP composite in comparison with the other systems, which is consistent with the results from the study of the composite interface In addition, the mechanical properties of the composites are improved by the fibre treatment, possibly thanks to the better interfacial adhesion The tensile testing of the composites was not highly successful to determine the full mechanical properties due to the premature failure of the composite samples, which shows a high defect sensitivity of the composites The impact strength of the UD coir/PP and coir/epoxy composites were obtained by Izod impact testing, which shows that the toughness of PP cannot be improved by adding coir fibres; while, for the brittle epoxy, coir fibres can improve the toughness with minimum a factor of five For coir/epoxy composites, the investigation of the effect of fibre loading on the composite impact strength shows there is an optimum value of fibre loading to obtain highest impact strength Moreover, the impact strength is also improved by alkali treatment of the fibres An initial study on coir-bamboo fibre hybrid composites with PP matrix was carried out, where the coir fibre and bamboo fibre were mixed at meso level by layer by layer stacking of UD fibre prepregs The result shows that a positive hybrid effect is obtained when a low bamboo fibre fraction is used, which leads to a higher composite strain at failure compared to mono bamboo fibre composite 6.2 Future work The study of the microstructure of the coir fibres showed that they have a high porosity with lumens in their elementary fibres This hollow structure of the fibres is expected to give good damping capacity In future research, the coir fibre composites should be characterised by vibration and acoustic damping tests The mechanical properties of coir fibre were obtained from single fibre tensile tests using different methods to measure reliable values for the fibre elongation Many tests need to be done to have a statistically distributed result Therefore, dry and impregnated fibre bundle tensile tests are recommended for determination of the fibre properties With these tests, the statistical data for a larger population will be obtained, which help to understand the mechanical properties of the fibres and to conveniently analyse the final composites’ behaviour 170 Chapter In wetting analysis of the fibres, the static equilibrium contact angles of the fibre in various test liquids were determined by two methods, which are fitting the dynamic angles by Molecular-kinetic theory and the relaxation of the liquid meniscus during static contact angle measurement with a tensiometer Another method will be considered, in which a sound vibration will be used to force the test liquid into equilibrium state during a static contact angle measurement, which is supposed to provide more reliable equilibrium contact angles Alkali treatment was used to modify the fibre surface for studying the composite interfacial adhesion and the mechanical properties of the composites More treatments should be applied on the fibre for further understating the fibre-matrix interfacial interaction and the composite properties It was found that the coir fibre can ameliorate the toughness of brittle epoxy This is an interesting result which should be further studied with other matrix systems The preliminary work on coir-bamboo fibre hybrid composites showed a potential use and application of coir fibre in composites An intensive study should be focused on this topic, in which several hybrid composites will be considered, by hybridisation with bamboo fibre or flax fibre The hybrid effect of the composites will be characterised on both the meso level (fibres are mixed at the scale of fibre layers), and micro level (mixing at single fibre level) Different fibre volume fractions will also be considered in analysis of the hybrid effect Appendix A 171 Appendix A Scanning set up and parameters for analysis of coir fibre using Skyscan Micro-CT in SEM (SEM-CT) The Skyscan Micro-CT attachment for the SEM Philips XL 30 FEG in the Department MTM allows visualisation and measurement of the 3D internal structure of an object, which can be applied for analysis of microstructure of natural fibres, like coir fibre The set up of the scanning equipment is shown in Figure 1, in which a Titanium target is used in combination with a SEM electron beam for producing X-rays The resolution of scanning images can be changed by adjusting the distance between the target and the sample Coir fibre sample Ti target Figure Set up for SEM-CT scan of coir fibre Appendix A 172 Sample specification for scanning with this equipment: Spatial resolution: from 350 nm to 8m Sample length: up to 8-10 mm Sample cross-section: 0.18 - 4mm Scanning parameters used for coir fibres: Source voltage of SEM: 30 kV Source current: 113-122 µA Image resolution: 1.8, 2.3 m (image pixel size) Exposure time: 4000 ms Gain: times The Skyscan software NRecon is used to reconstruct cross-section images from scanning projection images The reconstructed set of slices can be viewed in the Skyscan Data Viewer program And the analysis of fibre microstructure including morphology measurements, 2D/3D distances and angle measurements can be carried out using the software CTanalyser Appendix B 173 Appendix B Single fibre tensile testing with optical strain mapping Sample preparation for 2D mapping of fibre deformation The deformation of the fibre is measured using the image correlation technique, which tracks the movement of small speckles in a speckle pattern on the fibre surface Firstly, the speckles were created on the fibre surface by spraying black paint (coir fibre has a light colour) Due to the small area of the fibre surface, it is necessary to obtain a small size of speckles for a sufficient tracking in lateral image processing In case of coir fibre, the fibre elongation is high, hence a small test length (5 mm) was used to prevent the loss of tracking due to a large movement of the speckles (Figure 1) Speckles on coir fibre surface mm Figure Set up for fibre tensile test with strain mapping Appendix A 174 Image correlation for fibre strain measurement Images recorded by the camera during tensile loading are correlated for analysis of fibre displacement using the software Vic-2D The analysis procedure is as follows: Open the recorded images by selecting Speckles Images in the common task Select the analysed area on the fibre surface (using rectangle function R) Adjust the size of subset (small values for small sample size) Then, run the correlation process (using the green arrow button) A series of data files is created after finishing the correlation process These files are used for the strain analysis (select Data as shown in Figure 2) In the Plotting tools, the measurement of fibre strain can be set by selecting variable exy Appendix B 175 Select an area of interest (red rectangle line in Figure 2) Then, use function ‘inspect rectangle’, followed by ‘extract’ to get the result of fibre strain exy The distribution of fibre strain is presented as in Figure Figure Strain distribution of analysed coir fibre using image correlation 176 Appendix A Curriculum Vitae Personal data Name: Le Quan Ngoc Tran Date of birth: 23/01/1978 Nationality: Vietnamese Address: Schapenstraat 37/105 3000 Leuven Belgium GSM: +32 487 19 56 39 e-mail: Ngoc.Tran@mtm.kuleuven.be Education 2008 – present Ph.D., Materials Engineering, Katholieke Universiteit Leuven, Belgium Dissertation: Polymer composites based on coconut fibres 2002 – 2004 M.Sc., Materials Engineering: Polymers and Composites, Katholieke Universiteit Leuven, Belgium Thesis: Internal structure and mechanical properties of random long glass fibre composite 1994 – 1999 B.Sc., Chemical Engineering, Ho Chi Minh City University of Technology, Vietnam Thesis: Polymer blends of natural rubber and polyvinyl chloride Internship June 2006 Training on “Synthesis of nanomaterials” at ARC Centre for Functional Nanomaterials, The University of Queensland, Australia July-August 2004 Technical training on “Composites processing techniques” at Arplam NV, Arplama Group, Brugge, Belgium October-November Training on “Construction materials from natural fibres” at Technishe 2000 Universitaat Dresden, Germany Professional experience 2008 – present Research assistant in Composite Materials Group, KU Leuven, Belgium 2004 – 2008 Researcher and lecturer in Polymers and Composites at Can Tho University, Vietnam Publications Journal papers L.Q.N Tran, C.A Fuentes, C Dupont-Gillain, A.W Van Vuure, I Verpoest; Understanding the interfacial adhesion and compatibility of coir fibre thermoplastic composites; Composites Science and Technology (2012) (Submitted) C.A Fuentes, L.Q N Tran, C Dupont-Gillain, A.W Van Vuure, I Verpoest; Interfaces in natural fibre composites: effect of surface energy and physical adhesion; Journal of Biobased Materials and Bioenergy (2012) (Accepted) L.Q N Tran, C.A Fuentes, C Dupont-Gillain, A.W Van Vuure, I Verpoest; Wetting analysis and surface characterisation of coir fibres used as reinforcement for composites; Colloids and Surfaces A 337 (2011) 251-260 C.A Fuentes, L.Q N Tran, C Dupont-Gillain, A.W Van Vuure, I Verpoest; Wetting behavior and surface properties of bamboo fibres; Colloids and Surface A 380 (2011) 89 N Defoirdt, S Biswas, L De Vries, L.Q.N Tran, J Van Acker, Q Ahsan, L Gorbatikh, A Van Vuure, I Verpoest; Assessment of the tensile properties of coir, bamboo and jute fibre; Comp Part A 41 (2010) 588-595 Conference proceedings L.Q N Tran, C.A Fuentes, C Dupont-Gillain, A.W Van Vuure, I Verpoest; Coir fibre composites: from fibre properties to interfacial adhesion and mechanical properties of composites; ECCM 15 European Conference on Composite Materials, Venice, Italy; June 2012 L.Q.N Tran, C.A Fuentes, C Dupont-Gillain, A.W Van Vuure, I Verpoest; Investigation of the interfacial compatibility and adhesion of natural (coir) fibre thermoplastic composites; SAMPE Benelux student seminar, Ermelo, Netherlands; January 2012 L.Q.N Tran, C.A Fuentes, C Dupont-Gillain, A.W Van Vuure, I Verpoest; Investigating the interfacial compatibility and adhesion of coir fibre composites ; ICCM 18 International Conference on Composite Materials, Jeju, South Korea; August 2011 L.Q N Tran, C.A Fuentes, C Dupont-Gillain, A.W Van Vuure, I Verpoest; Interfacial adhesion and mechanical properties of unidirectional coir fibre composites; Ecocomp 4th International Conference on Sustainable Materials, Polymer and Composites; Birmingham, UK; July 2011 L.Q N Tran, C.A Fuentes, C Dupont-Gillain, A.W Van Vuure, I Verpoest; Wetting behaviour and surface characteristics of coconut (coir) fibres used as reinforcement for composites; ECCM 14 European Conference on Composite Materials, Budapest, Hungary; June 2010 L.Q N Tran, C.A Fuentes, C Dupont-Gillain, A.W Van Vuure, I Verpoest; Wetting behaviour and surface energy of coconut (coir) fibres; Natural Fibres 09’ International Conference, London, UK; London 2009 [...]... coconuts which are harvested after about 6-7 months on the plant (the green coconuts have thin copra and mainly provide coconut water for drinking) While brown fibre is obtained by harvesting fully mature coconuts of 11-12 months when the nutritious layer in the seed is ready to be processed into copra and desiccated coconut The brown fibres are stronger but less flexible than the white ones Coir fibres. .. different fibre extraction processes Natural fibres can be divided in subgroups based on their origins as plant fibres, animal or mineral fibres Figure 1-2 shows the three subgroups highlighting some common fibres used in composite materials Figure 1-3 Worldwide production of natural fibres, in million ton (Sources: FAOSTAT, 2009 and FAO, 2009) [6] The production volumes of natural fibres are shown in... with high content of lignin) [20, 21] Figure 1-8 shows the cross-section of a coconut consisting of the copra, the core shell and the husk shell Figure 1-8 Coconuts from the palm and cross section of a coconut (adapted from [21]) Traditionally, coir was extracted from husks that had been soaked for 6–9 months (retted) in sea water or lagoon water and then beaten with a wooden mallet The fibres were... publication xvi Introduction 1 Chapter 1 Introduction 2 Chapter 1 1.1 General introduction Composite materials, by which is usually meant fibre reinforced polymers, are used in a wide range of applications from aerospace, automotive and construction to leisure and sporting goods, where high mechanical properties in combination with light weight make them greatly attractive materials Moreover, these materials. .. with main components and a schematic representation of their organisation Climatic conditions and age not only influence the structure of the fibres but also the chemical composition [6, 8] To have efficient processing and quality improvement of the fibres, a good understanding of the fibre chemistry is Introduction 7 necessary In Table 1-1, the major chemical components of common natural fibres are presented... and considered as commodity in the world market Their production is estimated at around 1 million ton per year (FAOSTAT, 2009) at prices of order 30 to 40 Eurocents per kilo Introduction 13 1.2.2.1 Extraction of coir fibres Extraction of coir fibres from coconut husk shells is mainly carried out in the following steps: retting (the pre-treatment process in the traditional procedure), extraction of... mechanical properties Coir fibre composites will be reviewed with a focus on the composite impact properties Finally, there is a discussion on the fibre-matrix interface adhesion and some fibre treatments for improvement of the interface quality in natural fibre composites 1.2.1 Natural fibres Figure 1-2 Overview of natural fibres [2, 6, 7] Introduction 5 Natural fibres generally are fibres which are not synthesised... mechanical properties of plant fibres Figure 1-7 Schematics of possible cell wall organisation in (A) wood fibres, (B) bast fibres, (C) monocotyledonous plant fibres and (D) seed fibres Black lines indicate orientation of cellulose microfibrils; stress-strain curves of fibre with different density (E) and MFA (F) [6] The mechanical properties of plant fibres depend on the organisation of cell walls in terms... (700) 80-855 (600) Elongation at break (%), range (most frequently published) 15-50 (30) 2-10 (8) 2-3 1.3-6 (3) 0.2-3.1 (1.8) 1.2-4 (3) 1.9-14 (3) 1.2.2 Coir fibres Coconut fibres are usually known under the name ‘coir’ fibres in literature, and are obtained from the fruit of the coconut palm (Cocos nucifera L.) growing extensively in tropical countries Coconut palm is the most economically important... Other applications are coir nettings and geotextiles for soil protection and erosion control, and rubberised coir mats used in upholstery padding for automobiles Nowadays, there are three good reasons to use natural fibres, namely: economy, ecology and society; hence, coir fibres can be a good candidate as reinforcement for composite materials They are cheaper in cost than other natural fibres, easily