Thermoplastic foams from zein and gelatin

The aim of this study was to characterize the foaming of natural proteins as thermoplastic polymers. In particular, two proteins, one of vegetal origin, zein, and one of animal origin, gelatin, were processed to achieve thermoplastic polymers, and subsequently foamed by a gas foaming batch process. The effects of suitable plasticizing additives and melt-mixing process on the thermal and mechanical properties of the thermoplasticized proteins were evaluated to assess the thermoplastic characteristics of these materials. Furthermore, selected protein/plasticizers systems were foamed with mixtures of CO2 and N 2 as blowing agents, in a batch foaming apparatus, at different temperatures, pressures and pressure drop rates, to evaluate the processing windowand the final properties of the foams. Foams with densities of 0.1 g/cm3 and morphologies characterized by uniform distributions of cells with 10 l m diameters were obtained. Results indicate the suitability of zein and gelatin for being processed with classical thermoplastic processing technologies including melt mixing and foaming and their potentials as biodegradable polymers.