It is widely believed that plastics do not biodegrade, but this is in fact not the case. The concept of biodegradable plastics and polymers was first introduced in the 1980s. Bacteria that could break down plastic were developed as early as 1975, when team of Japanese scientists discovered a strain of Flavobacterium living in pools containing waste water from a nylon factory. At that time, two strains of bacteria were developed to breakdown nylon. Flavobasgteria and pseudomonas were found to possess enzymes (nylonase) capable of breaking nylon down. These two types of bacteria were not known to have existed before the invention of nylon in 1935.
Biodegradable plastics decompose through the action of living organisms, usually bacteria. There are two types of biodegradable plastics: bioplastics, plastics that are derived from renewable raw materials such as poly-3-hydroxybutyrate (PHB) and polyhydroxyvalerate (PHV) and plastics that contain biodegradable additives. The latter are derived from petrochemicals and contain additives that enhance biodegradation. While most aromatic polyesters are almost totally resistant to microbial attack, aliphatic polyesters are biodegradable because of their potentially hydrolysable ester bonds. Polylactic Acid (C3 H4 02 )n or PLA is a biodegradeable thermoplastic aliphatic polyester derived from renewable resources. PLA is somewhat misleading as is it not a polyacid but rather a polyester derived from renewable sources such as corn, tapioca roots, chips or starches and sugarcane. PLA has the second highest consumption of bioplastics in the world.
Biodegradable polymers are a specific type of polymer that result in by-products such as CO2, N2, H2O, biomass and inorganic salts when they break down. These plastics are found both naturally and synthetically and consist largely of ester, amide and ether groups. How they breakdown is determined by their structure and is often synthesized by condensation reactions as well as ring opening polymerization.
Biodegradable does not mean compostable. Compostable means that a material can be processed into compost or humus while biodegradable means a substance can be biologically broken down. At present there has been much debate about how efficient manufacturing bioplastics from natural materials really is. It takes 2.65 kg of corn to make 1 kg of polylactic acid, the most commonly available compostable plastic. 270 million tons of plastic are made every year to replace conventional plastic with corn-derived polylactic acid. This production removes 715.5 million tons of corn from the world food supply just at a time when global warming is reducing farm productivity. Today’s corn crops are used mainly for biofuels with 40% used for ethanol. 35% is used for animal food and only a small percentage is used as a food crop, mostly high-fructose corn syrup. While bacteria eating plastic may not be the ultimate solution for disposing of plastic, it is likely that bacteria does have the ability to consume hydrocarbons.
Biodegradable plastics are manufactured into packaging, bottles, jars, air pillow packaging, tea bags, pencil sharpeners and pens to name a few uses.
Questions? Comments? Let me know in the comments section below.
Interested in learning more about how plastics are made? Download our free plastic manufacturing glossary!