For over fifty years, heat stabilizers, light stabilizers, and antioxidants have been added to polymers to maintain their material properties by preventing their degradation. This chemical adjustment is necessary to extend the life of products such as plastic pipes, paints and coatings, and automotive parts. More recently, additives with the opposite purpose have become available: They are designed to enhance the biodegradation of hydrocarbon polymers used in common products such as plastic bags. Biodegradation is the breakdown of organic compounds by microorganisms or other biological means to their inorganic mineral constituents, such as carbon dioxide (CO2). Biodegradation additives would seem to be an elegant solution to the mounting environmental problem of plastic waste—except that recent research indicates they do not work. See also: Antioxidant; Biodegradation; Microbial ecology; Polymer; Polyolefin resins; Stabilizer (chemistry)
In February 2015, researchers from Michigan State University reported in the journal Environmental Science & Technology that none of the polymer-biodegradation-promoting additives that they tested speeded up the breakdown of the hydrocarbon compounds polyethylene or poly(ethylene terephthalate) during three years of composting (aerobic), anaerobic digestion (landfill simulation), or burial in soil. An earlier evaluation by E. F. Gómez and F. C. Michel Jr. of Ohio State University produced similar results for polyethylene and polypropylene that contained biodegradation-promoting additives; that is, the polymers did not show any significant degradation when tested in similar environments. See also: Polyester resins
Common biodegradation additives tested in both studies were the so-called oxo-biodegradable additives, which are salts of transition metals such as cobalt, iron, nickel, and manganese. Oxo-biodegradable additives are supposed to cause polyethylene and other polymers that are not compostable to break down to smaller pieces in the presence of oxygen and heat or ultraviolet light. It is these smaller pieces that are then expected to biodegrade. Landfills, however, are very poor settings for rapid degradation because heat, light, and oxygen are generally in short supply there. See also: Oxidation-reduction; Photodegradation; Transition elements; Ultraviolet radiation
According to the official guidelines defined by the U.S. Federal Trade Commission, for products to be marketed as biodegradable, they must be “completely returned to nature” within one year. In October 2014, the Federal Trade Commission warned 15 waste-bag marketers (whose names have not been made public) that their claims for oxo-biodegradability may be deceptive.