Effects of various plasticizers on the mechanical properties, water resistance and aging of thermo-moulded films made from sunflower proteins

The thermoplastic potential of a sunflower protein isolate (ISFP) was studied with the aim of obtaining films of biodegradable polymers. Several polyalcohols (ethylene glycol (EG), propylene glycol (PG), polyethylene glycols (PEGs), polypropylene glycols (PPGs)) were tested as protein plasticizing agents. Five plasticizers were chosen (glycerol, ethylene glycol, diethylene glycol, triethylene glycol and propylene glycol). These agents all produced soft, brown, smooth films with good mechanical properties (sigma(ma) = 6.2 -9.6 MPa; epsilon(max) = 23-140%) with a high level of impermeability to water vapor (1.9-9.9 x 10(-12) g m(-1) s(-1) Pa-1). However, these films were only moderately resistant to water (due to the migration of hydrophobic plasticizers into the water). Changes in the mechanical properties of these films also were studied over time and a loss of lowest-boiling point plasticizers was showed. However, no marked loss of glycerol or TEG was observed over the 3-month aging period. Thus, those plasticizers seems to be the most suitable plasticizers for sunflower proteins. (C) 2003 Elsevier Science B.V. All rights reserved.