Aligned flax fibre/polylactate composites: A materials model system to show the potential of biocomposites in engineering applications

The potential of biocomposites in engineering applications is demonstrated by using aligned flax fibre/polylactate composites as a materials model system. The failure stress of flax fibres is measured by tensile testing of single fibres and fibre bundles. For both fibre configurations, it is found that failure stress is decreased by increasing the tested fibre volume.

Based on two types of flax fibre preforms: carded sliver and unidirectional non-crimp fabric, aligned flax fibre/polylactate composites were fabricated with variable fibre content. The volumetric composition and tensile properties of the composite were measured. For composites with a fibre content of 37 % by volume, stiffness is about 20 GPa and failure stress is about 180 MPa.

The tensile properties of the composites are analysed with a modified rule of mixtures model, which includes the effect of porosity. The experimental results are well predicted by the model. The back-calculated effective stiffness and failure stress of the flax fibres are in the ranges 56-60 GPa and 515-730 MPa, respectively.

Finally, the model is used for parametric analysis and overall guidelines for the comparisons between tensile performance of flax fibre composites and traditional fibre composites (exemplified by glass fibre composites) are presented. The stiffness per volume, per weight and per cost is compared for these two types of composites.