As far as the tensile properties of natural fibres as reinforcements for composites are concerned, flax fibres will stay at the top-end. However, an efficient conversion of fibre properties into their corresponding composite properties has been a challenge, due to the fibre damages through the conventional textile methods utilised to process flax. These techniques impart disadvantageous features onto fibres at both micro- and meso-scale level, which in turn degrade the mechanical performances of flax fibre-reinforced composites (FFRC). Undulation of fibre is one of those detrimental features, which occurs during traditional fibre extraction from plant and fabric manufacturing routes. The undulation or waviness causes micro-compressive defects or ‘kink-bands’ in elementary flax fibres, which significantly undermines the performances of FFRC. Manufacturing flax fabric with minimal undulation could diminish the micro-compressive defects up to a substantial extent. In this research, nonwoven flax tapes of highly aligned flax fibres, blended with a small proportion of polylactic acid have been manufactured deploying a novel technique. Composites reinforced from those nonwoven tapes have been compared with composites reinforced with woven Hopsack fabrics and warp knitted unidirectional fabrics from flax, comprising undulating fibres. The composites reinforced with the highly aligned tapes have shown 33% higher fibre-bundle strength, and 57% higher fibre-bundle stiffness in comparison with the composites reinforced with Hopsack fabric. The results have been discussed in the light of fibre undulation, elementary fibre individualisation, homogeneity of fibre distribution, extent of resin rich areas and impregnation of the fibre lumens.
Lotfi A, Li H, Dao DV and Prusty G. Natural fiber -reinforced composites: A review on material, manufacturing, and machinability. Journal of Thermoplastic Composite Materials. 2019; 0892705719844546.
2.
AmiriAUlvenCAHuoS. Effect of chemical treatment of flax fiber and resin manipulation on service life of their composites using time-temperature superposition. Polymers2015; 7: 1965–1978.
3.
BaleyCBusnelFGrohensY, et al.Influence of chemical treatments on surface properties and adhesion of flax fibre–polyester resin. Compos Part A Appl Sci Manuf2006; 37: 1626–1637.
4.
BledzkiAFinkHPSpechtK. Unidirectional hemp and flax EP- and PP-composites: influence of defined fiber treatments. J Appl Polym Sci2004; 93: 2150–2156.
5.
JohnMJAnandjiwalaRD. Recent developments in chemical modification and characterization of natural fiber-reinforced composites. Polym Compos2008; 29: 187–207.
6.
Van de WeyenbergIChi TruongTVangrimdeB, et al.Improving the properties of UD flax fibre reinforced composites by applying an alkaline fibre treatment. Compos Part A Appl Sci Manuf2006; 37: 1368–1376.
7.
HasanRRayyaanR. Effect of fibre geometry on the tensile properties of thermoset jute fibre composites. Composites2014; 14: 18.
8.
ShahDUSchubelPJCliffordMJ. Modelling the effect of yarn twist on the tensile strength of unidirectional plant fibre yarn composites. J Compos Mater2013; 47: 425–436.
9.
RaoYFarrisRJ. A modeling and experimental study of the influence of twist on the mechanical properties of high-performance fiber yarns. J Appl Polym Sci2000; 77: 1938–1949.
NaikNKuchibhotlaR. Analytical study of strength and failure behaviour of plain weave fabric composites made of twisted yarns. Compos Part A Appl Sci Manuf2002; 33: 697–708.
13.
ChunH-JShinJ-YDanielIM. Effects of material and geometric nonlinearities on the tensile and compressive behavior of composite materials with fiber waviness. Compos Sci Technol2001; 61: 125–134.
14.
Davidson P, Waas AM, Yerramalli CS, et al. Effect of fiber waviness on the compressive strength of unidirectional carbon fiber composites. In: 53rd AIAA/ASME/ASCE/AHS/ASC structures, structural dynamics and materials conference, AIAA 2012-1612, Honolulu, Hawaii, 2012.
15.
GarnichMRKaramiG. Localized fiber waviness and implications for failure in unidirectional composites. J Compos Mater2005; 39: 1225–1245.
16.
HsiaoHMDanielIM. Effect of fiber waviness on stiffness and strength reduction of unidirectional composites under compressive loading. Compos Sci Technol1996; 56: 581–593.
17.
MahadikYHallettS. Effect of fabric compaction and yarn waviness on 3D woven composite compressive properties. Compos Part A Appl Sci Manuf2011; 42: 1592–1600.
18.
WisnomMRAtkinsonJ. Fibre waviness generation and measurement and its effect on compressive strength. J Reinforc Plast Compos2000; 19: 96–110.
19.
CharletKJernotJEveS, et al.Multi-scale morphological characterisation of flax: from the stem to the fibrils. Carbohydr Polym2010; 82: 54–61.
20.
MadsenBAslanMLilholtH. Fractographic observations of the microstructural characteristics of flax fibre composites. Compos Sci Technol2016; 123: 151–162.
21.
Batra S. Other long vegetable fibres: abaca, banana, sisal, henequen, flax, ramie, hemp, sunn, and coir. In: Menachem Lewin (ed), Handbook of fiber science and technology. Vol. 4. 1985, pp. 727–807, Boca Raton: Taylor & Francis Group.
22.
BosHDonaldA. In situ ESEM study of the deformation of elementary flax fibres. J Mater Sci1999; 34: 3029–3034.
23.
BaleyC. Analysis of the flax fibres tensile behaviour and analysis of the tensile stiffness increase. Compos Part A Appl Sci Manuf2002; 33: 939–948.
24.
BaleyC. Influence of kink bands on the tensile strength of flax fibers. J Mater Sci2004; 39: 331–334.
25.
Charlet K, Jernot J-P, Gomina M, et al. How the morphology of a flax fibre influences its mechanical behaviour. In: Proceedings of the 13th European conference on composite materials, Stockholm, Suède, 2008.
26.
BensadounFVerpoestIBaetsJ, et al.Impregnated fibre bundle test for natural fibres used in composites. J Reinforc Plast Compos2017; 36: 942–957.
27.
PageDElhosseinyFWinklerK, et al.Elastic modulus of single wood pulp fibers. Tappi1977; 60: 114–117.
28.
BosHMolenveldKTeunissenW, et al.Compressive behaviour of unidirectional flax fibre reinforced composites. J Mater Sci2004; 39: 2159–2168.
29.
HughesM. Defects in natural fibres: their origin, characteristics and implications for natural fibre-reinforced composites. J Mater Sci2012; 47: 599–609.
30.
Symington M, Banks W, Thomason J, et al. Kink bands in flax and hemp polyester composites. In: Proceedings of the 18th international conference on composites materials (ICCM'11), Jeju Island, Republic of Korea, 2011.
31.
BaetsJPlastriaDIvensJ, et al.Determination of the optimal flax fibre preparation for use in unidirectional flax–epoxy composites. J Reinforc Plast Compos2014; 33: 493–502.
32.
HughesMCarpenterJHillC. Deformation and fracture behaviour of flax fibre reinforced thermosetting polymer matrix composites. J Mater Sci2007; 42: 2499–2511.
33.
KhalfallahMAbbèsBAbbèsF, et al.Innovative flax tapes reinforced Acrodur biocomposites: a new alternative for automotive applications. Mater Des2014; 64: 116–126.
34.
MoothooJAllaouiSOuagneP, et al.A study of the tensile behaviour of flax tows and their potential for composite processing. Mater Des2014; 55: 764–772.
35.
MartinNDaviesPBaleyC. Comparison of the properties of scutched flax and flax tow for composite material reinforcement. Ind Crops Prod2014; 61: 284–292.
PiyatuchsananonTFuruyaARenB, et al.Effect of fiber waviness on tensile strength of a flax-sliver-reinforced composite material. Adv Mater Sci Eng2015; 2015: 1.
38.
CharletKJernotJ-PGominaM, et al.Mechanical properties of flax fibers and of the derived unidirectional composites. J Compos Mater2010; 44: 2887–2896.
39.
CullenRKSinghMMSummerscalesJ. Characterisation of natural fibre reinforcements and composites. J Compos2013; 2013: 1–4.
40.
KuHWangHPattarachaiyakoopN, et al.A review on the tensile properties of natural fiber reinforced polymer composites. Compos Part B Eng2011; 42: 856–873.
41.
SummerscalesJDissanayakeNPVirkAS, et al.A review of bast fibres and their composites. Part 1 – fibres as reinforcements. Compos Part A Appl Sci Manuf2010; 41: 1329–1335.
42.
CorollerGLefeuvreALe DuigouA, et al.Effect of flax fibres individualisation on tensile failure of flax/epoxy unidirectional composite. Compos Part A Appl Sci Manuf2013; 51: 62–70.
