Composite Materials from Unsaturated Polyester/Rice Husk Ash/ Natural Rubber-g-Polystyrene

Abstract

Composite materials from unsaturated polyester (UPE) resin, black rice husk ash (BRHA), and natural rubber grafted polystyrene (NR-g-PS) were prepared. NR-g-PS was synthesised by emulsion copolymerisation with a NR/styrene molar ratio of 80/20 using tert-butyl hydroperoxide/tetraethylene pentamine (t-BHPO/TEPA) as an initiator. Grafting efficiency of the copolymer product was about 54%. Initially, UPE was blended with BRHA at UPE/BRHA weight ratios of 100/30, 100/40 and 100/50. Each blend was subsequently mixed with NR-g-PS in the proportions of 5, 10 and 15 parts per hundred of UPE resin (phr). After curing, the cast specimens were examined for their physical properties, thermal expansion coefficient and morphology. It was found that the composite of 100UPE/30BRHA/5NR-g-PS exhibited the highest flexural and impact strength but the lowest water absorption. The thermal expansion coefficient of 100UPE/30BRHA/5NR-g-PS composite measured by thermomechanical analysis (TMA) was as low as 0.00005/°C. The morphology of the composites was investigated by scanning electron microscopy (SEM), which disclosed that NR-g-PS particles were well dispersed in the UPE matrix whereas the RHA was agglomerated and poorly dispersed in the composites. The higher the amount of NR-g-PS the more agglomeration of BRHA. This was due to the very high viscosity of the systems.