The effects of various reinforcing fillers in polypropylene have been studied. Composites containing different amounts (40, 50, and 60) of rice-husk (RH), wood fibre (WF) and bagasse (BG) fibres as the reinforcing fillers with polypropylene were prepared using a co-rotating twin screw extruder. The physical and mechanical properties of the samples were characterized. In order to increase the interphase adhesion between the components, polypropylene grafted maleic anhydride was added as a coupling agent to all compositions. It was found that the PP/WF composites had higher tensile and flexural strength compared with other composites. Flexural strength and flexural modulus of composites for all reinforcing fillers were improved, and impact strength and tensile strain decreased with increased fibre content. Water absorption of the composites increased with increased fiber content. In this respect, PP/BG composites, among other composites, showed the highest level of water absorption. SEM observations showed that, up to 50 wt% of fibres, more voids were formed in the composites which led to weak adhesion between the polymer matrix and the fibres and as a result the products showed lower tensile strength. Thermal analysis of the composites filled with 50 wt% fiber showed that better thermal stability was attained for PP/WF and PP/RH composites compared to their PP/BG counterpart.
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