Determining the minimum, critical and maximum fibre content for twisted yarn reinforced plant fibre composites

The effect of fibre volume fraction on the physical and tensile properties of aligned plant fibre composites (PFCs) produced via vacuum infusion has been investigated. There is no clear correlation between fibre volume fraction and porosity. However, low fibre content PFCs are prone to intra-yarn voids, while high fibre content PFCs are prone to inter-yarn voids. This is due to changing resin flow dynamics with increasing fibre content. The tensile behaviour of PFCs with increasing fibre content is similar to that of conventional fibre reinforced plastics (FRPs). Interestingly, the non-linear stress-strain response of plant fibres has been transferred to the composites. Fibre content and tensile properties are found to be linearly related, as per the rule of mixtures. A void content of up to 4% is found to have minimal effect on the tensile properties of PFCs. The minimum and critical (nu(f,crit)) fibre volume fractions for aligned flax and jute-polyester composites are found to be substantially higher than conventional aligned FRPs; nu(f,crit) it for jute-polyester and carbon-polyester is 8.1% and 2.4%, respectively. A simple model has also been developed to approximate the theoretical maximum obtainable fibre volume fraction of PFCs reinforced with staple fibre yarns. The absolute theoretical maximum fibre content is found to be 58.9%, which agrees with experimental values in literature. A high nu(f,crit) (similar to 10%) and low nu(f,max) (similar to 45%) implies that the range of useful fibre volume fractions for PFCs containing staple fibre twisted yarns is only 35%. (C) 2012 Elsevier Ltd. All rights reserved.