Retrogradation and Antiplasticization of Thermoplastic Starch

Petrochemical-based plastics are widely used in modern society due to their high effective mechanical and barrier properties (Farris et al., 2009; Siracusa et al., 2008). However, petrochemical-based plastics have become an environmental concern as they are not biodegradable or recyclable. Replacing the petrochemical-based polymers with biopolymers which are renewable has become an attractive idea and necessitates research on bioplastics (Debeaufort et al., 1998). Among the biopolymers, starch is considered as one of the most promising candidates for bioplastics due to its abundant availability, annually renewability, competitive price, and potential performance, including thermoplasticity (Lai & Padua, 1997; Mali et al., 2005). Native starch does not have thermoplastic properties. However, when additional plasticizers, elevated temperatures and shear are present, native starch does exhibit thermoplastic properties. Standard techniques, such as extrusion and injection moulding, used for producing petrochemical-based plastics, can be used in thermoplastic processing of starch (Guilbert et al., 1997). Some of thermoplastic starch (TPS) has been developed into commercial products, like compost bags, packaging materials (loose fillers and films), coatings, mulch films and disposable diapers (Jovanovic et al., 1997; Lai et al., 1997). TPS film and coating are being developed for the meat, poultry, seafood, fruit, vegetable, grains and candies industry sectors (Debeaufort et al., 1998). A drawback for use of starch is that TPS products age with time during storage due to starch retrogradation, which significantly changes quality, acceptability, and shelf-life of the TPS products. This review will summarize the current knowledge of TPS pertaining to its plasticization, retrogradation, and antiplasticization.