9 - Biodegradable and Biobased Polymers

Abstract

The utilization of natural polymers for nonfood uses can be traced back far to ancient time. New developments have allowed them to be used as a material component in polymer blends and composites to make biodegradable products. For example, starch is traditionally the largest source of carbohydrates in human diet. Being polysaccharide polymers, starch has been intensively studied in order to process it into a thermoplastic polymer in the hope of partially replacing some petrochemical polymers. The resultant melt-processable starch is often termed thermoplastic starch (TPS). To destruct the crystalline structure of starch and allow flowability, large contents of plasticizers are used in the preparation of TPS. Depending on the amount of plasticizers used, TPS materials range from glassy to rubbery state. In addition, cellulosic natural fibers have long been used as load-bearing materials to reinforce polymer matrix. Similar to starch and cellulose, Soy protein plastic (SP) is an abundant, lowcost, and renewable biopolymer which shows great potential in polymer industry as a replacement for petrochemical polymers in many applications. SP is commercially available in three different SP concentrations: soy flour, SP concentrate, and SPI. Biodegradable polymers could be either natural or synthetic polymers and they could be derived from either renewable or nonrenewable resources. Nonbiodegradable polymers could also be derived from renewable feedstock, e.g., Dupont's Sorona, which is poly(trimethylene terephthalate) using the corn-derived 1,3-propanediol as the diol monomer. Developing biodegradable polymers from renewable resources appears to be the best scenario in the development of “green” materials and processing techniques.