Photo-oxidation starch

Amylose has been shown to degrade by photo-oxidation and hydrolysis reactions on exposure to ultraviolet (Phillips, 1980), resulting in breaking of the chain and production of organic acids. Empirically, paste films have been found to be more stable if they are made from starch granules rather than flour (Clapp, 1978 Wills, 1984), whose gluten (protein) content will degrade faster (Radley, 1976). The paste made from flour has better proper-... 

TGA showed that the LDPE samples all degraded around 480 °C. For the LDPE stabilised with corn starch and pro-oxidant (LDPE-MB) polymer a second shoulder appeared around 318-327 °C. The mechanism for photo-oxidation and thermooxidation starts with the formation of free radicals on the main chain, with subsequent formation of peroxy radicals. Later, intra- and inter-molecular reactions lead to the formation of hydroperoxides. 

Generally [17] starch is added at fairly low concentrations (6-15%) the overall disintegration of these materials is achieved by the use of transition metal compounds, soluble in the thermoplastic matrix, as pro-oxidant additives that catalyse the photo and thermo-oxidative process [18-21]. 

Starch can be nsed as a natural filler in traditional plastics (11,23-33) and par-ticnlarly in polyolefins. When blended with starch beads, polyethylene films (34) biodeteriorate on exposure to a soil environment. The microbial consumption of the starch component, in fact, leads to increased porosity, void formation, and the loss of integrity of the plastic matrix. Generally (32,35-38), starch is added at fairly low concentrations (6-15%) the overall disintegration of these materials is achieved by the use of transition-metal compounds, soluble in the thermoplastic matrix, as pro-oxidant additives which catalyze the photo- and thermooxidative process (39-44). 

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