ScienceAsia 23 (1997): 135-158 |doi: 10.2306/scienceasia1513-1874.1997.23.135

DEGRADATION OF CASSAVA STARCH-POLYETHYLENE BLENDS

SUDA KIATKAMJORNWONG^a, THANIDA PABUNRUANG^b, NIPON
WONGVISETSIRIKUL^c, AND PATTARAPAN PRASASSARAKICH^d

ABSTRACT: Degradable polyethylene films containing 0-20% w/w of cassava starch, 0-2% w/w of soya oil and 0-0.1% w/w ferric stearate were dispersed with Epolene wax in a dry blend mixer and compounded in a two-roll mill to form sheets. The sheets were cut into small chips that were then extruded in a blown film molding machine to yield polyethylene films. The oxidative degradation of the films was measured by outdoor weathering testing in comparison with indoor testing, and soil burial testing for six months under a natural atmosphere. Biodegradation of the films was determined by measurement of the populations of Aspergillus niger and Penicillium pinophilum fungi. All degradation processes were followed by monitoring chemical and physical changes of the samples by infrared spectroscopy, average molecular weights by the viscosity method, and tensile properties. FTIR spectroscopy revealed the formation of the carbonyl group as the ketone functionality during degradation. The concentrations of the carbonyl group were high in iron stearate starch-filled PE films. The populations of Aspergillus niger and Penicillium pinophilum on the samples showed that the latter had a much higher population, indicating that it efficiently promoted biodegradation of the starch-filled PE film in the presence of soya oil and iron stearate. The films were disintegrated into minute pieces containing abundant holes of destroyed starch. The iron stearate starch-PE films lost their physical properties after two months of outdoor exposure. Unlike the outdoor exposure test, the starch containing PE films by a soil burial test took a longer time to degrade. Both physical and mechanical properties of the PE films kept indoors (unexposed) remained unchanged for longer than six months under ambient conditions.

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a Department of Photographic Science and Printing Technology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand.
b Multidisciplinary Program of Petrochemistry-Polymer, Graduate School, Chulalongkorn University, Bangkok 10330, Thailand.
c Department of Chemistry, King Mongkut's Institute of Technology, Lardkrabang, Bangkok, Thailand.
d Department of Chemical Technology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand.

Received 5 january, 1997