Proteins are interesting raw materials for plastics. They can be considered natures polyamides. Besides being a renewable resource they are in several cases available as cheap side streams from existing industrial processes. Examples are wheat gluten from wheat starch/fuel production, whey from cheese production and rape proteins from biodiesel production. Most proteins are stiff and brittle because of the many hydrogen bonds, but can be made softer and tougher by the use of a plasticiser. One of the most effective plasticisers for these is glycerol. Glycerol is also a side stream product, from biodiesel production. Hence it is possible to produce a tough protein plastic entirely made from by-products. A drawback with protein plastics, as well as oil-based polyamides (e.g. PA6, PA66), although to a lesser extent, are their moisture sensitivity. This limits their use to indoor applications. The most important issue to consider when replacing oil-based plastics with those that are protein-based is that the latter must be able to run on conventional plastic processing equipments. Hence they need to be extrudable, injection mouldable and compression mouldable. On obstacle here, in contrast to thermoplastics, is that the temperature range where they can be processed is narrow. If the temperature becomes too high the protein aggregates and cross-link to such as extent that the viscosity increases drastically. Compression moulding is in general more suitable for protein plastics but extrusion and injection moulding are more “important” production techniques. In this presentation the extrusion of wheat gluten and <i>Crambe Abyssinica</i> protein (industrial oil crop) is discussed and problems and possibilities highlighted.<br/> <br/>

Extrusion of protein plastics

253rd National Meeting (2017)

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