Biodegradable Plastics
Most of the world's plastics are made from hydrocarbons, specifically oil and petroleum products that take hundreds of years to disintegrate once they are thrown away. However, there are indications that tomorrow's plastics will be made from materials that are more quickly and completely biodegradable than oil-based plastics. Plastics of this sort may one day be discarded in backyard compost piles.
During the 1980s, compostable bags made of polyethylene plus starch first came upon the market. These early biodegradable bags caused disappointment when it was discovered they did not totally degrade, but left polyethylene residues that were invisible to the naked eye and difficult to find by normal chemical analysis. Soil scientists expressed concern that the polyethylene fragments might accumulate in soils and hinder both microbial and plant growth. The test of true biodegradability, they argued, is whether in a composting environment 100 percent of the carbon of the material will mineralize and convert to carbon dioxide.
In 1990 the British-based company Imperial Chemical Industries (ICI) released a material called Biopol, used to manufacture shampoo bottles. Biopol is made from a plastic called PHB-V, which is produced from bacteria and glucose. When thrown away, this material is broken down by the microorganisms present in waste and decomposed completely within a couple of months.
Other versions of biodegradable plastics have been developed in the United States. In 1991 Procter and Gamble, Du Pont, and Exxon funded bacteria-based plastic research at a number of academic institutions, including the University of Massachusetts at Amherst. In addition, Battelle, a private research company, produced a completely biodegradable plastic from vegetable oils. Other research and development efforts have shown that plastics can be made from other glucose-intensive materials such as potato scraps, corn, molasses, and beets.
Even though the general concept of truly biodegradable plastics and the specific development of Biopol was exciting, the cost of manufacturing these plastics proved to be much higher than the cost of making oil-based plastics. In 1990 biodegradable plastics were seven times more costly to produce than standard oil-based plastics.
By 1997, compostable bags still sold for more than nondegradable bags, but this did not take into account the high cost of removing nondegradable plastic at composting facilities. The outlook for biodegradable plastics thus appeared to depend on success in developing applications that favored composting versus landfilling.
Again in 1997, examples of both natural and synthetic biodegradable polymers were known. One synthetic polymer used in biodegradable plastic bags was an aliphatic polyester called polycaprolactone, marketed by Union Carbide. Another biodegradable plastic film called MaterBi contained corn starch and other proprietary ingredients. Corn was also used to make polylactic acid for Cargill's EcoPLA biopolymer. Research was underway at the University of Michigan on a material called Envar consisting of an alloy of caprolactone and a thermoplastic starch.
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