The Optimisation of Flax Fibre Yarns for the Development of High-Performance Natural Fibre Composites

Abstract

Currently most developments in the area of natural fibre reinforced composites have focused on random discontinuous fibre composite systems. The development of continuous fibre reinforced composites is, however, essential for manufacturing materials, which can be used in load-bearing/structural applications. The main problem in this case is the optimisation of the yarn to be used to manufacture the textile reinforcement. Low twisted yarns display a very low strength when tested dry in air and therefore they can not be used in processes such as pultrusion or textile manufacturing routes. On the other hand, by increasing the level of twist, a degradation of the mechanical properties is observed in impregnated yarns (e.g. unidirectional composites) similar to off-axis composites. Additionally, a high level of twist decreases the permeability of the yarns. This problem is addressed in the current work using yarns based on both long and short flax fibres.

Development of Flax Fibre based Textile Reinforcements for Composite Applications

“…The DOS-2 fabric was used (see Table II). This fabric is composed of non-optimised (highly twisted) yarns (223 turns/m) [12]. Nonetheless, the obtained properties are quite high compared to the current state of the art non-woven flax based composites despite the relatively low fibre volume fractions.…”

“…In order to create yarns for textile applications, typical flax fibre yarns have relatively high levels of twist, giving them the necessary strength for textile processing and end use. However, when highly twisted yarns (see Figure 2) are impregnated in a polymer resin, their strength may decrease significantly with twist similar to the drop in strength of an off-axis composite [11,12]. Moreover, due to the high level of twist the permeability of the yarns decreases and impregnation becomes more difficult.…”

“…An important parameter in the development of these yarns is the level of twist. It has been shown by Goutianos and Peijs [12] that very low twisted yarns display a very low strength when tested in air and therefore they cannot be used in processes such as pultrusion or textile manufacturing routes like knitting or weaving (see Figure 2).…”

Modelling the effect of yarn twist on the tensile strength of unidirectional plant fibre yarn composites

“…[4][5][6] However, due to the short length of technical plant fibres, the manufacture of aligned unidirectional PFCs requires the reinforcement to be in the form of staple fibre yarns. 4,[6][7][8][9][10][11][12] Plant fibre yarns, whose primary application is found in textiles, are conventionally produced through ring-spinning. The spinning process gives the yarn a twisted structure, where twist is the primary binding mechanism.…”

A review of bast fibres and their composites: Part 3 – Modelling

“…(37) is similar in form to that used to model the effect of microfibril angle on the elastic modulus of single plant fibres by McLaughlin and Tait [94]. The cos 2 (2a) model was found to be a near-perfect fit for experimental data from Goutianos and Peijs [95] for aligned flax yarn composites with either 609 tex long fibres or 1000 tex short fibres at seven different twist levels.…”