Starch plastic composites

Figure 1. Possible routes for biological and chemical degradation of starch-plastic composites. Note that direct biological degradation of petrochemical-based polymers does not occur. Rather, these polymers must first undergo chemical degradation to form as yet uncharacterized, lower molecular weight intermediates.

Starch-plastic composites contain a mixture of two very different types of materials (/) hydrophobic, petrochemical-derived polymers (PE, EAA) known to be highly resistant to degradation by living organisms, and (i7) a hydrophilic, natural polymer (starch) that is easily broken down by a wide array of organisms. In the process developed by Otey (3), these fundamentally incompatible materials are forced into an intimate mixture during production of the plastic film. Since... 

At this point little is known about the interrelationships between composition, structure, starch-degradation and physical disintegration properties of starch-plastic composites. Continued work towards development of a laboratory assay for biodegradability will eventually result in the establishment of a sufficient database to elucidate these relationships, allowing development of a host of starch-containing plastic products for both existing and new markets. 

Breslin, V. T. Swanson, R. L. (1993). Deterioration of starch-plastic composites in the... 

Breslin, V.T., 1993, Degradation of starch-plastic composites in a municipal solid waste... 

Imam, S.H., Gordon, S.H., Buigess-Cassler, A., and Greene, R.V., 1995, Accessibility of starch to enzymatic degradation in injection-molded starch-plastic composites. J. Environ. Polym. Degrad. 3 107-113. 

For these reasons there has been renewed interest in starch-based plastics in recent years. Earlier studies of starch esters and ethers (3-10) indicated that they had inadequate properties in comparison with cellulose derivatives for most applications. More recently, starch graft copolymers (2), starch plastic composites (11,12), and starch itself (13-17) have been proposed as plastic materials. 

As com starch is a native agricultural product, inexpensive (about 10 cents lb ) and available annually in multimillion ton quantities it could be considered a replacement for petroleum-based plastics as starch-graft copolymers, starch-plastic composites, and starch itself. [52]. 

Extrusion is the preferred method for compounding gelatinized starch plastic composite materials, although batch mixing is also effective. The processing temperature is below 230°C, that is the decomposition temperature of the starch. The high shear destroyed the starch granules in minimal time. 

The starch removal from starch-plastic composites by amylose is evidenced in the FT-IR spectrum of starch-EAA-PE treated with Bacillus sp XI amylase for 72 h at room temperature. The carbohydrate -OH and C-O absorbance bands are drastically reduced— Fig. 4. 

Patents and applications assigned to Fertec in Italy describe starch plastic composites that are reputed to be totally degradable [58]. 

Bouwer EJ (1992) Bioremediation of organic contaminants in the subsurface. In Mitchell R (ed) Environmental microbiology. Wiley, New York, pp 319—333 Brandi H, Gross RA, Lenz RW, Fuller RC (1988) Pseudomonas oleovorans as a source of poly(P-hydroxyalkanoates) for potential application as biodegradable polyesters. Appl Environ Microbiol 54 1977—1982 Breslin VT (1993) Degradation of starch-plastic composites in a munidpal solid waste landfiU. J Environ Polym Degr 1 127—141... 

Breslin VT, Swanson RL (1993) Deterioration of starch-plastic composite in the environment. J Air Waste Manag Assoc 43 325-335 Breslin CB, Chen C, Mansfeld F (1997) The electrochemical behaviour of stainless steels following surface modification in cerium-containing solutions. Corrosion Sci 39 1061-1073... 

More recently, starch graft copolymers [15-19], starch plastic composites [20-21], and starch itself [22-25], have been proposed as plastic materials. 

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