Utilization of Starch in Plastics

Starch utilization in plastic and rubber compositions began in the 60s and 70s, with oxidised starch in rubber and other polymers, such as urethane foams, poly(vinyl alcohol) and copolymers of poly(ethylene-co-acrylic acid) formulations, and as a filler in plasticized polyvinyl chloride (PVC) [37,39]. In another technique, gelatinized starch was mixed with PVC latex and the water was removed to give a PVC-starch composition, which was mixed with a PVC plasticizer such as dioctyl phthalate (DOP). 

The introduction of gelatinized starch expanded considerably the use of starch as a polymeric material, but this technology based on water processing was limited by the necessity of more than one step, some of which were discontinuous. Nonetheless, these developments showed that it was possible to produce blends of synthetic thermoplastic materials with gelatinized starch, affording new prospects of the utilization of starch as a plastic material in the production of films and injection-moulded goods. 

The extrusion of starch with relatively low water contents (15 - 25% w/w) was extensively studied by the food industry [43]. One of the first commercial products of starch that achieved very good results was the expanded starch used for protection and as a shock absorber in packages, as a replacement for expanded polystyrene. These materials were patented by the National Starch Chemical Investment Corporation [44]. 

A different approach was used by the Ferruzy Company, the main difference being the use of high boiling-point plasticizer instead of water for the destructuration of starch. In this technology, starch was plasticized together with polymers such as polyethylene-vinyl alcohol (EVOH), EAA, poly-e-caprolactone, with small amounts of moisture, in a twin-screw extruder [49], to produce an intimate mixture between starch and the synthetic polymer. The commercial trade name of this product family is Mater-Bi . 

Owing to the method and the type of plasticizer used for TPS production, the process leads to the destruction of the starch granule lamellar structure, giving rise to a quasi-amorphous or semi-crystalline material. 

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