Starch-polyester Graft Copolymer

Thermoplastic polymer foams can be prepared from starch-polyester graft copol zmers. Water is used as the plasticizer as well as the blowing agent (3). The foams have improved processability, surface properties, and an extended range of mechanical properties. 

An alkylaryl ammonium hectorite clay, from the BENTONE series may be also used as additive. The clay provides excellent mechanical strength, flame retardancy and highly improved gas barrier properties (32). 

Still another starch-polyester graft copolymer and a chemically modified starch-polyester graft copolymer composition has been described. The starch-polyester graft copol5mers are synthesized by the reaction of starch with biodegradable polyester polymers in the presence of maleic acid and glycerol as plasticizer. Examples of biodegradable polyesters are summarized in Table 7.6. 

Poly(butylene adipate-co-terephthalate) Poly(vinylacetate-co-vinylalcohol) 

Maleic acid acts as a transesterification catalyst. The composition can be produced continuously in a twin screw corotating extruder. The starch-polyester graft copolymer can be solvent cast, melt cast and blown into clear transparent film particularly for use in single use disposable applications and can be biodegradable (32). 

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R. Narayan, S. Balakrishnan, Y. Nabar, J.-M. Raquez, and P. Dubois, Starch-polyester biodegradable graft copolymers and a method of preparation thereof, US Patent 7 985 794, assigned to Board of Trustees of Michigan State University (East Lansing, MI), July 26,2011. 

In the context of this chapter, the use of thermoplastic starch in blends with thermoplastic resins is of the main interest. As shown in Table 16.11, several blends have been developed, e.g., with vinyl alcohol copolymers (EVAl), polyolefins, aliphatic polyesters such as poly-e-caprolactone (PCL) and its copolymers, or polymers of glycols (e.g., 1,4-butanediol) with succinic, sebacic, adipic, azelaic, decanoic or brassihc acids, PCL + PVC. Compatibilization is possible by amylose/EVAl V-type complexes, starch grafted polyesters, chain extenders like diisocyanates, epoxies, etc. [Bastioli et al., 1992, 1993]. 

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