Egg white-based bioplastics developed by thermomechanical processing

The development of new protein-based biomaterials has been receiving increasing interest in the last few years. This paper is focused on the development of new bioplastic materials, based on wheat gluten and egg white proteins, manufactured by direct mixing of proteins with a plasticizer,, glycerol, and, eventually, a thermal and moulding process which shapes the material and gives them suitable mechanical properties to be used as substitutive materials of synthetic polymers for definite applications. These rheological properties have been evaluated by shear rheology and dynamic mechanical thermal analysis on both intermediate process materials and final bioplastics. Moreover, the microstructure of the samples has been characterized by atomic force microscopy and modulated differential scanning calorimetry. Glycerol-protein mixtures have been proved to hold suitable rhelogical behaviour and thermosetting potential for further processing, by means of a compression-moulding process, to obtain bioplastics. Glycerol/egg white blends (0.5 ratio) can be more easily processed, because of their rheological behaviour at ca. 50 degrees C. On the contrary, glycerol/wheat gluten blends (0.5 ratio) need longer mixing times and more severe thermosetting conditions, although lower values of the bioplastic storage modulus are obtained in the whole range of temperature studied. (C) 2007 Elsevier Ltd. All rights reserved.