Thermo-mechanical performance of poly(lactic acid)/flax fibre-reinforced biocomposites

• Flax/PLA samples found suitable for load bearing structural applications.
• Effect of temperature (20–120 °C) the thermomechanical properties explained.
• In-depth study on strain rate effect on the material and its viscous behaviour explored.
• An increase of the storage modulus observed after 80 °C explained.

In this study, the thermo-mechanical performance of flax fibre reinforced poly lactic acid (PLA) biocomposites was investigated for the potential use in load bearing application such as body-in-white and body structures in the automotive sector. Focus was given into the relationships between the thermal and mechanical properties, and the material response under different loading and environmental conditions. The strength (72 MPa) and stiffness (13 GPa) of flax/PLA composites investigated indicate a very promising material to replace traditional choices in load bearing application. The PLA’s crystallinity was measured to approximately 27%. Annealing above 100 °C for an hour decreased that value to 30%, but analysis of tensile results of annealed specimens reveals a significant reduction of both the tensile strength and modulus. This reduction is associated with micro-cracking that occurred on the surface of PLA during the heating as well as deterioration of the flax properties due to drying. The study results show that strength and modulus increased with increasing strain rates, while elongation at break reduces respectively. A modulus of 22 GPa was recorded in 4.2 m/s crosshead velocity. Further, flax/PLA showed significantly higher modulus than flax/epoxy for the composites studied. Improvement of the interfacial bonding and the temperature characteristics, combined the thermoplastic nature of PLA, demonstrates that flax/PLA composites is ideal for use in structural automotive applications.