Influence of maleated polystyrene on the mechanical properties of bio-based fibers-polystyrene composites

Abstract

Bio-based polymer composites are gaining importance day by day as there has been a dramatic increase of interest in using bio-fibers as fillers in composites. The main bottlenecks in the broad use of bio-based fibers in thermoplastics have been the poor compatibility and lack of interfacial adhesion between the polar bio-based fibers and non-polar thermoplastic which results in inferior mechanical properties. Strength of composites can be enhanced if the interfacial adhesion is improved which can be carried out by using coupling agents. In this paper, mechanical properties of bio-fiber composites prepared with two types of fillers (wood fiber and wood flour) at four concentrations (10, 20, 30 and 40 %) using 5 wt% of maleic anhydride-co-polystyrene (MAPS) as coupling agent and a thermoplastics-polystyrene (general purpose polystyrene-grade SC 208) having a melt flow index of 20 g/10 min are described in detail. The tensile strength of the coupled composites increased from 31 to 49 MPa when filler concentration was increased from 10 to 30 %. Further increase in filler content to 40 % reduces the tensile strength slightly to 44 MPa. Similar trends were observed in case of wood flour-polystyrene composites. The tensile strength increased from 31 to 41.5 MPa at 30 % filler loading and then decreased to 36.6 MPa at 40 % loading, which showed an increase of 33 % in tensile strength over virgin polystyrene. Flexural strength of wood fiber-polystyrene composite prepared with MAPS as coupling agent increased linearly with fiber concentration. The flexural strength increased from 54 MPa for unfilled polystyrene to 94.5 MPa for 40 % fiber loading, exhibiting a 74 % increment over unfilled polystyrene. Wood flour filled polystyrene composites exhibited a linear increase with filler loading. For un-coupled composites, the tensile and flexural strengths were almost constant at all the loadings. Tensile modulus of coupled and uncoupled composites reinforced with wood fiber and wood flour increases linearly with filler loadings. The increase in mechanical properties provided evidence of increased interfacial adhesion and effective stress transfer from low modulus matrix to high modulus fibers.