Biodegradable protein-nanoparticle composites

K DEAN and L YU, CSIRO - Manufacturing and Infrastructure Technology, Australia 

The focus of this chapter is plant protein. Chickpea and soy protein isolates (Salmoral et al, 2000) are two of the more common plant proteins that are used to produce biodegradable plastic film materials. However, there are many other proteins used in film production, including wheat (Bejosano and Corke, 1999), pistachio (Ma et al, 2002), sunflower (Orliac et al, 2003) and peas (Gueguen et al, 1998). Proteins are formed by the condensation polymerisation of various combinations of amino acid repeat units and different plant sources produce proteins with different amino acid combinations and thus exhibit different properties (McGrath and Kaplan, 1997). Their general structure is illustrated in Fig. 11.1. 

Commercially available soy products include soy isolate, soy concentrate and soy flours (Kumar et al, 2002 Paetau et al, 1994). Soy protein isolates are generally used in the preparation of soy-based plastics due to their high protein content (approximately 90%) (Paetau et al, 1994) and are generally prepared from an alkaline suspension of defatted soy flour which is acidified to the isotonic point at which the proteins precipitate. The precipitated proteins are 

Irradiation of proteins to promote crosslinking has been reported by a number of authors including Salmoral et al (2000) and Mezgheni et al, (Mezgheni et al, 2000). These authors utilised gamma-irradiation to produce crosslinked films and solid samples and this work showed that irradiated films had better mechanical properties and were quite resistant to water. 

Montmorillonite, hectorite and saponite are frequently used pristine layered silicates which are combined with polymeric materials to form nanocomposites 

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