Rheological Properties of Dynamically Vulcanised Thermoplastic Elastomer Composites of Polypropylene, Ethylene Propylene Diene Terpolymer and White Rice Husk Ash: Temperature Dependence

Abstract

Kesan suhu pengekstrudan terhadap sifat–sifat reologi pemvulkanan dinamik bagi komposit getah dominan PP/EPDM/WRHA telah dikaji. Empat suhu yang berbeza digunakan bermula daripada 170 sehingga 200°C dengan selang suhu sebanyak 10°C. Adunan getah dominan PP/EPDM tanpa pengisi juga turut dikaji bagi tujuan perbandingan. Kajian menunjukkan bahawa komposit boleh diproses secara termoplastik, jika suhu ekstruder dan kadar ricih yang sesuai digunakan. Kajian terhadap lengkungan aliran dan rekahan leburan ekstrudat menunjukkan peningkatan suhu pengekstrudan telah meningkatkan kelikatan leburan bagi komposit pada kadar ricih yang rendah. Pada kadar ricih yang tinggi, pola yang didapati adalah berlawanan. Didapati komposit PP/EPDM/WRHA adalah pseudoplastik bersamaan dengan adunan PP/EPDM tanpa pengisi. Sifat pseudoplastik bagi system tervulkan ini seperti yang telah ditetapkan oleh indeks hukum kuasa (power law index, n) meningkat dengan peningkatan suhu pengestrudan. Di samping itu telah didapati penambahan bahan pengisi dan partikel–partikel getah tersambung silang mempamerkan kelakuan pseudoplastik di dalam leburan polimer tersebut. Penggantian separa matriks polimer dengan WRHA mengurangkan kesan ini, menunjukkan kelebihan pemprosesan WRHA terisi komposit. Kajian keseluruhan menunjukkan bahawa suhu 180°C sesuai untuk pengekstrudan kedua–dua komposit tanpa terisi dan terisi. Kata kunci: sifat reologi; pemvulkanan dinamik; elastomer termoplastik; poli propilena; etilene; polipropilene diene terpolimer; abu sekam padi putih The effects of extrusion temperature on rheological properties of dynamically vulcanized and rubber dominant composites of polypropylene (PP), ethylene propylene diene terpolymer (EPDM) and white rice husk ash (WRHA) were investigated. Four different temperatures varying from 170 to 200°C with 10 degree intervals were used. Filler free rubber dominant PP/EPDM blends were also subjected to the same study for the purpose of comparison. The study reveals that the composites could be processed like thermoplastics, if suitable extrusion temperatures and shear rates are used. Study of flow curves and melt fracture of extrudates indicates that increase in extrusion temperature increased the melt viscosity of the composites at low shear rates. At high shear rates, the trend becomes opposite. It was found that PP/EPDM/WRHA composites are pseudoplastic similar to the unfilled PP/EPDM blends. Pseudoplasticity of these vulcanized systems as judged by the power law index (n) increased as the extrusion temperature increases. Furthermore, it was shown that both incorporation of filler and introduction of crosslinked rubber particles induce the pseudoplastic behaviour in the polymer melts. Partial replacement of polymer matrices by WRHA reduces this effect indicating a processing advantage of WRHA filled ternary composites. Overall study suggests that temperature of 180°C is suitable for the extrusion of both these unfilled and filled composites. Key words: Rheological properties; dynamically vulcanized; thermoplastic elastomer; polypropylene; ethylene propylene diene terpolymer; white rice husk ash