Thermal degradation of biodegradable edible films based on xanthan and starches from different sources

Films based on xanthan/wheat starch and xanthan/maize starch were prepared in different proportions and analysed in terms of thermal stability in relation to the degradation reaction in an inert atmosphere. The main gaseous decomposition products were identified by infrared spectroscopy. Xanthan was found to be less thermally stable than starch from different sources. The starch addition to xanthan induced an increase in the film thermal stabilities. The thermal degradation mechanism of xanthan starts with scission of the side chain groups with subsequent scission of the main chain. Starches from maize and wheat presented a constant mechanism of thermal degradation. The proportion of xanthan/starch (50/50) presented a synergistic behaviour which may be associated with changes in the mechanism of the thermal degradation process. The FTIR spectra of the gaseous products during thermal degradation of xanthan showed a broad absorption in the 2750-3300 cm(-1) region, probably indicating decomposition of beta-D-mannopyranosyl groups, present in xanthan side chains. For pure starches, absorptions related to alcohol O-H stretching (3500-3750 cm(-1)), C=O stretching of CO2, CO and carbonyl compounds (2361, 2177 and 1743 cm(-1) respectively) were observed. For xanthan/starch mixtures (50/50) the same compounds as those for the pure polymer degradation were evolved. However, a shift of the C=O to higher wavenumber values indicates that new carbonyl compounds are being formed due to changes in the thermal degradation mechanism. (c) 2005 Elsevier Ltd. All rights reserved.