Novel sisal/flax braided hybrid natural fibre yarns for composite applications

Abstract

Exploring the use of natural fibres over synthetic fibres is crucial for advancing towards a more sustainable future. However, the structural applications of natural fibres, have largely been restricted to more expensive options such as flax. In this context, sisal fibres emerged as a compelling alternative due to lower cost and relatively high mechanical properties. The potential of sisal has been limited by difficulties in large-scale industrial processing. For instance, spinning sisal has proven difficult, particularly for tex values below 900. On the other hand, Flax yarns of various tex can be found in the market and are relatively stable in terms of consistency and other properties. To address these challenges, this study investigates innovative methods for preparing sisal fibres for industrial applications, by facilitating weaving into mats to be later infused with bio-resins. Apart from spinning, braiding of the individual fibres was adopted. A simple 3-strand braid consisting of sisal or flax only fibres and an intrayarn hybrid braided system was analysed. The configurations tested varied by the level of hybridisation: Neat Sisal (100% Sisal, 0% Flax), Sisal 76% with Flax 24%, Sisal 33% with Flax 67%, and neat Flax (0% Sisal, 100% Flax). Notably, the mechanical properties of the neat Flax braid were superior. The hybrids demonstrated lower properties compared to the yarns and the neat braided samples but offered a favourable balance in terms of mechanical properties, cost, manufacturing solutions and finer yarns. Comparative pull-out tests demonstrated that the braided yarns had higher interfacial shear strength than spun counterparts, showing potential in composite applications such as pultruded parts and fibre reinforcements of structures.