Mechanical and biodegradability properties of hydroxypropyl and cross-linked starch-Low density polyethylene (LDPE) Composite

Abstract

Disposal of synthetic polymers such as Low density polyethylene (LDPE) used in packaging materials are now considered as a serious environmental hazard because they are non-biodegradable. This research aims to produce biodegradable polymers by incorporating a bio-polymer (starch) into its polymeric matrix. Native starch from sorghum grain was modified by hydroxypropylation with propylene oxide and by cross-linking using epichlorohydrin. Biodegradable composites were prepared by blending the sorghum starches with Low density polyethylene (LDPE) at 1%, 3%, and 5% ww-1, using 2% ww-1 ethylene-bis-stearamide as the binding agent, and the blends were thereafter extruded. The mechanical properties, water absorption, and thermal properties of the starch–LDPE composites were determined. Soil burial test was carried out for six months to evaluate the biodegradation rate of the composites. Cross-linked Starch–LDPE Composites (CSC) and Hydroxypropyl Starch–LDPE Composites (PSC) exhibited improved tensile strength and yield elongation compared with the Native Starch–LDPE Composites (NSC). The water absorption capacity of the starch–LDPE composite increased from 0.05% (in LDPE) to 3.25% (in 5% PSC). Thermal behavior of the composites showed two-stage degradation, the main stage occurring in the range 430 – 648°C. Incorporation of starch into the LDPE matrix improved the biodegradation rate significantly from 0.55% (in LDPE) to 65.45% (3% PSC), 80.66% (5% PSC) in the starch-LDPE composites. Key words; biodegradation, composite, starch, Low Density Polyethylene