Starch-containing plastics, biodegradation

At this point little is known about the interrelationships between composition, structure, starch-degradation and physical disintegration properties of starch-plastic composites. Continued work towards development of a laboratory assay for biodegradability will eventually result in the establishment of a sufficient database to elucidate these relationships, allowing development of a host of starch-containing plastic products for both existing and new markets. 

JM Gould, SH Gordon, LB Dexter, CL Swanson. Biodegradation of starch-containing plastics. In JE Glass, G Swift, ed.. Biodegradability and Utilization, Washington DC Am Chem Soc, 1990, pp 65-76. 

This starting position makes a. one of the most important raw materials in the production of biodegradable - starch plastics as well as a component in starch-filled synthetics or in ->starch-containing plastics. In such systems, firmness, elasticity and flexibility is enhanced with rising a. content whereas the amylopeetin eomponent imparts brittleness and lower firmness. Therefore, a high a. content is demanded for most applications of starchy materials in biodegradable plastics as well as in many other applications as RR. 

Biologically degradable s. consist of merely - starch, - high amylose starch, esters or ethers of starchy materials and added plasticizers. They discern from - starch containing plastics in that starchy materials are the only polymer component in s. which contribute to the continuous phase (matrix). Their biodegradibility is superior to all starch containing plastics. 

Tokiwa Y., Takagi S., Koyama M. Starch-containing biodegradable plastic and method of producing same. American patent US5256711 (1993). 

Starch-Based Plastics. As can be seen in Table 8.7, a variety of starch-based plastics have been produced by several companies. Starch-based plastics are often water-soluble as well as biodegradable. Some contain almost entirely starch others contain blends of starch with other biodegradable components. 

This led some environmental groups, such as the Environmental Defense Fund (EDF) and the Environmental Action Foundation (EAF), to call for a consumer boycott of degradable plastics. In contrast to these materials, starch-based plastics have been developed which are truly biodegradable. Some contain nearly 100% starch, and others are blends of starch with other biodegradable components. Most use carefully controlled amounts of water as a plasticizer to convert the starch into a thermoplastic, along with careftilly controlled temperature and pressure. 

Cellulose, which is more fibrous than wood flour, is used as a filler for urea and melamine plastics. Melamine dishware is a laminated structure consisting of molded resin-impregnated paper. Starch and soybean derivatives are biodegradable, and the rate of disintegration of resin composites containing these fillers may be controlled by the amount of these fillers present in polymers. 

In 2006, there are around 30 major companies worldwide that are actively involved in developing biodegradable plastic materials. The synthetic biopolymers market is dominated by large, global and vertically integrated chemical companies such as BASF, DuPont, and Mitsubishi Gas Chemicals. The starch and PLA sectors contain mainly specialist biopolymer companies such as Novamont, NatureWorks, Rodenburg Biopolymers and Biotec, which were specifically established purely to develop biodegradable polymers. 

Biopolymer Technologies (Biop) offers a starch-based material containing an additive consisting of a vinyl alcohol/vinyl acetate copolymer. In 2005, the company transferred production of its bioplastics from The Netherlands to Schwarzheide in Germany and invested 7m in a new plant there, increasing its production capacity to 10,000 tonnes per annum. The announcement followed the decision earlier in 2005 by BASF to produce its Ecoflex biodegradable plastic, one of the components of Biop s Biopar resins, at the Schwarzheide site. 

Starch-based biodegradable plastics are used for the manufacture of thermoformed trays and containers for packaging fresh food and convenience food. 

It may be noted from Figure 1 that the starch molecule contains two important functional groups, that is the —OH group, which is important for substitution reactions, and C—O—C, which is susceptible to chain breakage. As a result of these two important features, starch and its derivatives are used in the synthesis of biodegradable plastics (1). 

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