Toddy Palm (Borassus Flabellifer) Fruit Fibre Bundles as Reinforcement in Polylactide (PLA) Composites: An Overview About Fibre and Composite Characteristics

Toddy palm fruit have an apparent density below 0.8 g/cm3 and offer an interesting lightweight construction potential in polylactide (PLA) composites reinforced with 37 mass-% fibres. Single fibre bundles show similar mechanical properties compared with coir: tensile strength of 240 MPa, Young's modulus of 3.8 GPa and an elongation at break of 31%. However, density and diameter (∼ 50 μm) of fruit fibre bundles are significantly lower. The compression moulded composites have a density of 0.9 g/cm3 and achieved an unnotched Charpy impact strength of 12 kJ/m2, a tensile strength of 25 MPa, Young's modulus of 1.9 GPa and an elongation at break of 9%. Due to the high porosity of the composites and the different stress-strain behaviour of fibre and matrix the fibre-reinforcement potential could not be fully used. Maximum stress of the composite was reached at the elongation at break of the PLA-matrix (∼2%) while the fibre achieved its maximum stress at an elongation of ∼31%. After reaching the maximum stress of the composite, the fibres were pulled out from the matrix with low energy absorption, resulting in a decrease in stress and a limited reinforcement potential. Additionally, the study investigates whether an insect attack by the Asian fruit fly on the mesocarp has a significant influence on the mechanical fibre characteristics. The results have shown that only the rough surface of the fibre bundles is smoothed by insect infestation. The mechanical properties were not significantly affected. For this reason insect-infested fruits of the toddy palm, which are no longer suitable for food production, can be used for the production of sustainable composite materials.