Thermal Decomposition Investigation of Soy Protein Isolate-Sodium Alginate Composite Membranes

A novel composite film of soy protein isolate and sodium alginate was fabricated by the aqueous solution casting method. The thermal decomposition behavior of the film was examined by thermogravimetric analyzer at the air flow rate of 30 ml/min, under heating rates of 5, 10, 15, 20 and 30 K/min and from ambient temperature up to 1250 K. As reflected by the weight loss results, the decomposition was composed of four phases and dependent on the heat rate. Based on the analysis of the variation in weight loss rate, the main thermal decomposition in the range of 420 - 630 K was found to be the first order reaction and the final residue was sodium oxide. Using kinetic models, the apparent activation energy and the frequency factor InA, calculated for the composite, were within 145.31 - 157.89 kJ/mol and 31.10 - 34.65 min(-1), respectively.