Thermoplastic cassava starch/sorbitol-modified montmorillonite nanocomposites blended with low density polyethylene: properties and biodegradability study

S Chuayjuljit, S Hosililak, A Athisart

Abstract


The objective of this research paper is to prepare environmentally friendly plastic materials from biodegradable cassava starch, montmorillonite (MMT) and low density polyethylene (LDPE). MMT was first modified by sorbitol via a solid state method. Results from X-ray diffraction (XRD) indicated that sorbitol molecules were intercalated in between MMT layers along 001 direction. Cassava starch was plasticized with sorbitol and formamide on a two-roll mill to obtain thermoplastic starch (TPS). The TPS/modified-MMT nanocomposites were prepared by means of melt blending of TPS with various amounts of MMT (0, 2, 4, and 6 phr). XRD and transmission electron microscopy (TEM) results showed that the nanocomposites formed were all exfoliated. The prepared nanocomposites were subsequently blended with a mixture of 80 LDPE/20 PE wax on a two-roll mill followed by a compression molding machine. The obtained polymer blends were examined for their impact and flexural strength, water absorption, morphology and biodegradability. The mechanical properties of LDPE were improved by incorporating 10 phr of TPS nanocomposite that contained MMT 2 phr and gained the highest impact and flexural strengths of 2900 J m-2 and 17 N m-2, respectively. The scanning electron micrographs displayed that the TPS nanocomposites with a high loading of starch and MMT exhibited poor distribution in PE matrix. Water absorption and biodegradability of the nanocomposites were enhanced with the increasing amount of cassava starch. However, silicate layers with high aspect ratio could serve as a barrier and reduce the water-uptake ability of these materials.

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