A Commercial Starch Based Polymer

 
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However, pure starch is not suitable as a polymer for packaging materials: it will not form a film (and hence cannot be manufactured in thin sheets). If you doubt this, try forming a film from rice or a potato! Also, pure starch does not blend with a polymer that can form a film.

What if we chemically modify starch? Australian researchers have in fact developed a way to chemically modify starch by substituting some -OH groups. Essentially the reaction is a hydroxypropylation of starch in batch reactor. This increases the hydrophobicity of starch, thus allowing it to blending with a synthetically-derived organic polymer.

This process has been developed by Dr Peter Halley (University of Queensland) while he was working within the former Cooperative Research Centre for International Food Manufacturing and Packaging Science.

Already a new product is currently being commercialized. It is a blend of a synthetically-derived organic polymer (from fossil-fuel resources) and the new polymer made from starch (which is a renewable resource, made for example from corn or potatoes). The product is intended to replace mulch film in agriculture - instead of laying down non-biodegradable plastic in the field to prevent weed growth, farmers can use this new biodegradable product, whose fate is to be ploughed into the field after it has served it's purpose.

The synthetically-derived organic polymer that forms the other part of the blend is a polyester made from three monomers:

1,4-butandiol
succinic acid
adipic acid

Each monomer has two reactive ends and can undergo a condensation reaction. The result is a polyester, and the reaction is analogous to the way nylon is formed from a dibasic amine and a diprotic acid - see Module 9.5.2 for comparison.

The starch replaces some of the oil-based polymer, and of course starch is a renewable resource. However, that is not all. The presence of starch makes the product biodegradable.

Large scale field trials with capsicum and tomato crops have been successful with the starch/synthetic blend. Films were ploughed into the soil and the material fully in the soil degraded completely.


Field trials of the new product