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Use in Polymers
Maintaining the particulate form during compounding is difficult, as processing temperatures need to be below the crystal melting point, which is itself influenced by moisture and plasticizers. Thermal decomposition of the starch also needs to be avoided. Under optimum conditions, the maximum practical temperature is about 230 °C.
Despite their apparent attractiveness, there is little sign of commercial interest in particulate starch beads as opposed to thermoplastic blends or nanocrystals. This is probably due to a number of issues, including water sensitivity, thermal instability, and cost of production. In support of this, there is also little literature on the use of starch beads as polymer fillers. Hashimi (1983) does describe their use in high-density polyethylene. Bastioli (2002) has reviewed starch-polymer composites but most of this concerns blends, rather than particulate reinforcements. The main commercial interest so far would seem to be from tire companies such as Goodyear Tire and Rubber (US Patent 5,672,639 to a starch reinforced rubber composition and tire). Working in conjunction with Novamont and BMW, Goodyear went on to develop tires using starch as a partial replacement for precipitated silica or carbon black fillers, and these have been commercialized. It seems that, while often referred to in the trade literature as a starch filler, it is more probable that a blend morphology is actually present.
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