Corn starch/EVOH overcomes hitch

22 January 1996 00:00  [Source: ICB]

RESEARCHERS AT the Massachusetts Institute of Technology (MIT) have developed a biodegradable material combining corn starch and an ethylene vinyl alcohol (EVOH) polymer, to stop the material becoming soft or brittle in changing atmospheric conditions.

A team led by Edwin Thomas of the Department of Materials Science & Engineering has focused on creating a 1 micron-thick surface with the protective properties of pure plastic.

By varying the ratio of the ethylene and vinyl alcohol components in the EVOH, properties ranging from non-biodegradable PE to water-soluble, biodegradable PVOH can be obtained.

Since the EVOH has a lower molecular weight, surface tension and viscosity than the starch component, it moves up to the surface because it is more attracted to the air interface. Once the product is discarded and shredded, the heavier starch is exposed to the elements.

Meanwhile, an improved grade of Novamont's starch-based biodegradable film which degrades in 45 days in composting conditions has met decomposing criteria from the Organic Reclamation and Composting Association. Novamont has also improved the physical properties of its Mater-Bi ZF03U film.

These films are designed to perform as standard plastics in industrial applications. An important use is in degradable bags for waste collection. The films and bags are produced by traditional ldPE film blowing and sealing techniques with minor modifications.

Other starch-based biodegradable materials produced by Novamont include a product containing EVOH copolymers, a replacement for PS packaging foams, and a completely natural material for rigid and dimensionally-stable injection moulded items.

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