Polylactic acid (PLA), a biodegradable polymer, a natural substitute made from fermented plant starch (usually corn) is quickly becoming a popular alternative to traditional petroleum-based plastics. PLA can be unmade by chemical hydrolysis that reduces the molecular weight of the polymer into tactic acid fragments. This is further degraded by microorganisms into carbon dioxide and water.
How is PLA made? Firstly corn is milled, separating starch from the raw material. The starch is processed into dextrose that is then converted to lactic acid using a fermentation process. Through condensation, the monomer lactide is formed and then purified through vacuum distillation. Using a solvent free process the lactide is polymerized into PLA resin.
As an increasing number of countries are banning plastic bags responsible for pollution, PLA is poised to play a big role as a viable, biodegradable replacement. However, PLA is far from dealing with the world's plastic waste problem because of several issues listed below:
* PLA biodegrades slowly- it could break down into its constituent parts (Carbon dioxide and water) within three months in a “controlled composting environment,” that is, an industrial composting facility heated to 75°C and fed a steady diet of digestive microbes. But it will take far longer in a compost bin or in a landfill packed tightly so that no light and little oxygen are available to assist in the process. Indeed, analysts estimate that a PLA bottle could take anywhere from 100 to 1,000 years to decompose in a landfill.
* Because of its different origin from regular plastic, it must be kept separate during recycling to prevent contamination of the recycling stream. Hence the plant-based PLA needs to head to a composing facility, not a recycling facility when it has out served its usefulness.
* The physical handling, storing, using and disposal of PLA requires great caution. Processed resin should be sealed until ready to use and unused material should be promptly resealed. PLA polymers are combustible and, once ignited, could burn rapidly under the right conditions of heat and oxygen. Controlling of dusts is necessary for safe handling of the product. Workers should be protected from the possibility of contact with molten resin during processing. Processing may emit fumes, which may include polymer fragments and other decomposition products. As far as their physical nature goes, PLA pellets are benign in terms of the environment. But if integrated into the marine environment and ingested by waterfowl or aquatic life, the pellets may mechanically cause adverse effects. Plastics made from PLA should not be discarded into sewers, on the ground or any body of water.
* Future costs to the environment and human health of genetic modification are still largely unknown and could be very high. The largest producer of PLA in the world is NatureWorks, a subsidiary of Cargill, which is the world's largest provider of genetically modified corn seed. With increasing demand for corn, Cargill and others have been tampering with genes to produce higher yields. Cargill Dow is also investigating ways to generate PLA including the use of renewable fuels from plants such as wheat, beets and other crops best suited to particular climates.
On the pro side, even though the resin has a natural base, it does have an impact on fossil fuel consumption. Making plastic from plants requires energy from coal and natural gas to power processing plants. But, the environmental key to manufacturing PLA is that it uses 20-50% fewer fossil resources than does making plastics from oil.