Development of biodegradable polymer materials from corn gluten meal

Abstract

Feasibility studies on isolation of com protein (zein) from com gluten meal (CGM) by various methods were carried out to identify the most effective procedure. It was found that of the methods that were investigated extraction of zein using 88% aqueous isopropanol is the most appropriate and useful method. Zein extracted from CGM was characterised by Kjeldahl protein determination, gel electrophoresis, thermal analysis and infra-red spectroscopy, and used to produce plasticised films and sheets with a variety plasticisers and additives, such as PEG 400, PVA, oleic acid, glycerol, fatty acids, fatty oils, corn starch, natural rubber latex. Zein blended with comstarch and oleic acid was used to prepare edible, biodegradable composite films and sheets, whose oxygen and water vapour barrier properties and mechanical properties were evaluated. Those experiments showed that zeirEstarch/oleic acid composite films have barrier properties that are appropriate for edible coatings and packaging films for food and pharmaceutical products. Further improvement of water resistance was achieved by using natural rubber as a component of zein-based blends. A modified alkali ripening/acid coagulation technique was developed to prepare mouldable, multi-component composite from zein, for applications as thermoplastic resins. Zein resins with additives such as natural rubber and poly (vinyl alcohol) were processed by rolling, compression moulding and injection moulding. Some of these resins showed improved water resistance and enhancement of other mechanical properties while maintaining biodegradability. Improved physical and barrier properties were observed when plasticised zein extracted from CGM was reactively blended with the synthetic biodegradable aliphatic polyester poly (butylene succinate) (Skygreen SG 100) in a Brabender Plasticorder at elevated temperatures. To avoid the need for isolation of zein from CGM5 a major focus of this work was utilisation of CGM as raw material for the development Ofbiodegradable resins derived, to as large an extent as possible, from renewable resources. Injection mouldable composite resins based on CGM plasticized with propylene glycol and mixed with SG 100 and (in some cases) wood fibre, were developed and characterised by dynamic mechanical thermal analysis, scanning electron microscopy, water absorption determination, measurement of mechanical properties, and evaluation of biodegradability in soil. Mathematical models derived from an experimental design software package were developed to estimate the variation of properties with the composition of the composites. The SG 100 component improved water resistance and tensile strength, while CGM and wood fibre increased Young's modulus, and CGM increased biodegradation rate in proportion to the CGM content of the composites.