bioplastic

/buy'oh plas"tik/, n.

plastic suitable for use as a biomaterial.

[1980-85; BIO- + PLASTIC]

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      moldable plastic material made up of chemical compounds that are derived from or synthesized by microbes such as bacteria or by genetically modified plants (genetically modified organism). Unlike traditional plastics, which are derived from petroleum, bioplastics are obtained from renewable resources, and they are biodegradable.

      Plastics are polymers (polymer)—assemblies of identical chemical subunits, called monomers, that are linked together in the form of a chain. The properties of a plastic, like those of all polymers, are defined by the monomers in the chain and by the number of links and cross-links in its structure. Cross-linking of the monomers increases a polymer's rigidity and thermal stability. As their name suggests, plastics can readily be molded into various shapes. Plastics such as polystyrene (polymerized styrene, CH₂=CHC₆H₅), polyethylene (polymerized ethylene, CH₂=CH₂), or polypropylene (polymerized propylene, CH₂=CHCH₃) are molded into a wide variety of everyday and specialized products—for instance, eating utensils, coffee cups, synthetic fabrics, park benches, automobile parts, and surgical implants.

      Since the early 20th century, there has been an explosion in the development and use of plastics, and their utility and importance have become so great that it is difficult to imagine modern life without them. Virtually all current plastics are derived from petroleum through chemical extraction and synthesis. Because petroleum-based plastics are generally not biodegradable, plastic refuse is very durable, and disposing of it has become a serious problem. Despite efforts to encourage and support recycling, landfills are becoming filled with plastic refuse, which also accumulates in the environment. An additional problem with petroleum-based plastics is that petroleum resources are being used up; conservative sources estimate that at current rates of consumption, all known sources of petroleum on Earth will have been depleted before the end of the 21st century. Given that modern life is dependent on plastics, that petroleum is a nonrenewable resource, and that petroleum-derived plastic waste fouls the environment, a sustainable solution for the longer term may be found in bioplastics.

      The first known bioplastic, polyhydroxybutyrate (PHB), was discovered in 1926 by a French researcher, Maurice Lemoigne, from his work with the bacterium Bacillus megaterium. The significance of Lemoigne's discovery was overlooked for many decades, in large part because, at the time, petroleum was inexpensive and abundant. The petroleum crisis of the mid-1970s brought renewed interest in finding alternatives to petroleum-based products. The rise of molecular genetics (heredity) and recombinant DNA technology after that time further spurred research, so that by the beginning of the 21st century the structures, methods of production, and applications for numerous types of bioplastics had become established. Bioplastics that were either in use or under study included PHB and polyhydroxyalkanoate (PHA), both of which are synthesized within specialized microbes, as well as polylactic acid (PLA), which is polymerized from lactic acid monomers produced by microbial fermentation of plant-derived sugars and starches. Degradation of the chemical links between the monomers in these plastics is brought about by microorganisms or by water, making bioplastics highly desirable materials for fabrication into biodegradable bottles and packaging film. In addition, because the degradation products are natural metabolites, the polymers are of interest in medical applications, such as controlled-release drug packaging and absorbable surgical sutures.

      Bioplastics currently make up an insignificant portion of total world production of plastics. Commercial manufacturing processes are plagued by low yields and are expensive. However, improvements in metabolic and genetic engineering have produced strains of microbes and plants that may significantly improve yields and production capabilities while reducing overall costs. These factors, when added to increasing oil prices and growing environmental awareness, may expand the market for bioplastics in the future.

Judith Fridovich-Keil

 

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