Influence of material parameters on the mechanical properties of extruded sisal fibre-polypropylene composites

Sisal fibres possess good reinforcing capability when compounded with polymers. These fibres are relatively inexpensive and have favourable specific strength and modulus values. They are also found in abundance and originate from renewable resources. Thermoplastic polymers such as polypropylene (PP) possess shorter manufacturing cycle times and reprocessability despite poor fibre wetting and high viscosity problems. The renewable natural fibres when coupled with the recyclable thermoplastic polymers provide eco-friendly natural fibre reinforced composites exhibiting attractive properties. Natural fibre thermoplastic composites are commonly manufactured by film stacking (compression moulding), injection moulding, pultrusion and extrusion. The current study focuses on maximising mechanical properties of thin sisal-PP extruded composite sheets. A factorial experimental design as a function of material formulation was applied to maximise the mechanical properties of the composites. An increase of 14% and ∼23% in the tensile and impact strength respectively, compared to PP was observed by setting the factors at levels predicted in the experiment. The fracture surfaces observed under SEM to investigate the fracture mode, revealed fibre fracture indicating a good fibre-matrix interaction and fibre pull-out. The fibre length checks revealed that most of the fibres were under the critical fibre length. Hence, failure of the fibres of critical length and higher may have initiated the failure of the material, followed by the yielding of the matrix and the pulling out of all the fibres that were under the critical fibre length.