Processing aids for re-processing starch-filled plastics

Abstract

Environmental threats restrict the use of nondegradable polymers and encourage the development and use of degradable plastics. In order to obtain a cost-effective biodegradable plastic, starch-filled polyethylene (PE) is still the best alternative. Starch and PE blend is incompatible at the molecular level and often leads to poor performance. In order to overcome this drawback, either PE or starch should be modified. The aim of this study was to modified linear low-density polyethylene (LLDPE) and blend it with starch. Maleic anhydride (MA) was grafted onto LLDPE in xylene using dicumyl peroxide (DCP) as an initiator. Corn starch in varying concentrations (between 10 and 60%) was blended with MA-g-LLDPE in a torque rheometer. The same blend compositions of nonfunctional LLDPE with the starch were prepared for comparative studies. The torque and totalized torque generated during blending are reported as a function of starch content. Torque decreased with increasing starch content for the compositions from 10 to 50% and increased for 60% starch content. Work energy decreased for all the compositions of blends except for 60% starch content. Tensile strength and modulus increased and percentage elongation decreased as the starch content increased in the blends. Water absorption of the blends increased with an increase in starch content. The biodegradability of MA-g-LLDPE/starch blends have been studied in two biotic environments: (1) soil environment over a period of 6 months; (2) mixed fungi inoculum (Aspergillus niger, Penicillium funiculosum, Chaetomium globosum, Gliocladium virens and Pullularia pullulans) for 28 days. The samples containing more than 30% starch content supported heavy fungus growth. Blends exposed to a soil environment degraded more than in fungi alone. Any changes in the various properties of the MA-g-LLDPE/starch before and after degradation were monitored using FTIR spectroscopy, weight loss, a scanning electron microscope (SEM) for surface morphology, a differential scanning calorimeter (DSC) for crystallinity and a thermogravimetric analyzer (TGA) for rapid determination of starch content. Percentage crystallinity decreased as the starch content increased and biodegradation resulted in an increase of crystallinity in MA-g-LLDPE/starch blends.