Determining the minimum, critical and maximum fibre content for twisted yarn reinforced plant fibre 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 (vf,crit) fibre volume fractions for aligned flax and jute-polyester composites are found to be substantially higher than conventional aligned FRPs; vf,crit 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 vf,crit (∼10%) and low vf,max (∼45%) implies that the range of useful fibre volume fractions for PFCs containing staple fibre twisted yarns is only 35%.