White rice husk ash (WRHA) and silica ®lled ethylene±propylene±diene terpolymer (EPDM) vulcanizates were prepared using a laboratory size two-roll mill. Curing characteristics and physical properties of vulcanizates were studied with respect to the ®ller loading and ®ller type. Filler loading was varied from 0±50 parts per hundred resin (phr) at 10 phr intervals. Curing was carried out using a semi-ef®cient vulcanization system in a Monsanto rheometer. Enhancement of the curing rate was observed with increasing WRHA loading, whereas the opposite trend was observed for silica-®lled vulcanizates. It was also indicated by the maximum torque and Mooney viscosity results that WRHA offers processing advantages over silica. Compared to the silica-®lled vulcanizates, the effect of ®ller loading on the physical properties of WRHA-®lled vulcanizates was not signi®cant. According to these observations, WRHA could be used as a diluent ®ller for EPDM rubber, while silica can be used as a reinforcing ®ller.

ABSTRACT:The performance of white rice husk ash (WRHA) as filler for polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM) thermoplastic elastomer (TPE) composites was investigated. The composites with different filler loadings were prepared in a Brabender plasticorder internal mixer. Both unvulcanized and dynamically vulcanized composites were prepared. Mixing and vulcanization processes of the composites were monitored through the typical Brabender torque-time curves. The mechanical properties and morphology of the composites were also studied. The Brabender torque curves revealed that the dynamic vulcanization process employed was successful and incorporation of filler has no adverse effect on the processibility of the composites. Incorporation of WRHA improves the tensile modulus and flexural modulus and lowers tensile strength, elongation at break, tear strength, and toughness of both types of composites. Dynamic vulcanization significantly enhances the mechanical and TPE properties of the composites. Dynamic mechanical analysis (DMA) study revealed the existence of two phases in both types of composites. It further shows that neither dynamic vulcanization nor filler agglomeration has played a prominent role in the compatibility of the composites. Thermogravimetric investigation shows that dynamic vulcanization or WRHA loading has not adversely affected the thermal stability of the composites. The scanning electron micrographs provide evidence for the tendency to form filler agglomerates with increasing filler loading, better filler dispersion of dynamically vulcanized composites over unvulcanized composites, and effective vulcanization of elastomer phase of the composites in the presence of filler.

This paper compares the processability, mechanical properties, and water absorption behavior of polypropylene (PP) composites filled with white rice husk ash (WRHA) and silica. It is shown that preparation of WRHA filled composites requires less energy than silica filled composites. WRHA-PP composites exhibit better impact properties while other mechanical properties are better in silica filled composites. WRHA-PP composites also showed a better resistance to the water absorption in comparison to silica composites. An increase in water uptake with increase in filler loading was observed for both fillers although the difference is not significant for WRHA-PP composites. The study further shows that the area of the specimen cut edges influences the water uptake. The effect of water uptake on tensile properties was also briefly examined.

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