Thermoplastic starch and their blends

7 Starch gelatinisation process (a) raw starch granules made up of amylose (linear) and amylopectin (branched) (b) addition of water breaks up crystallinity and disrupts helices (c)) addition of heat and more water causes swelling, amylose diffuses out of the granule (d) granules, mostly containing amylopectin, are collapsed and held in a matrix of amylose (adapted from Lai and Kokini, 1991). 

All systems were generally plasticised with urea and other polyols. Doane 

Ratto et al. (1999) has examined poly butylenes sueeinate adipate (PBSA) terpolymer/granular starch composites for blown films and showed they could produce good film tensile properties and control biodegradation with granular starch addition. Thermoplastic starch/cellulose fibre extrudates and injection moulded products were examined by Funke et al. (1998) and they showed a reduction in water adsorption with increasing fibre content. Work by Halley et al. (2001) examined the use of thermoplastic starch-polyester blends for use in mulch film applications noting excellent field performance and biodegradability for these materials. 

Modified processing techniques have also been useful for thermoplastic starch polymers. Recent work by Martin et al. (2001) and Martin and Avemous (2002) has examined the use of coextruded sheet processing to produce polyester/thermoplastic wheat starch/polyester multilayer films. It was found that adhesion strength between the layers and stability of the interface were crucial properties in controlling the final performance properties of the films. Work by Sousa et al. (2000) has also examined use of the novel shear controlled orientation injection moulding (SCORIM) process to control morphologies and provide tensile property increases of thermoplastic starch/synthetic blends. 

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