Biodegradable plastics are made of polymers from a natural and renewable source like wheat or corn starch. These polymers are more accessible to microorganisms in the environment that can break down the substances. Traditional plastics are made of polymers that are too long and too tightly linked for the decomposer organisms to break down. Considering how much stuff is made of plastics in our daily life, these persistent plastics will be a hazard to our environment for a long, long time.
Bioplastics can be made from starch, a carbohydrate energy storage in plants such as corn and wheat. However, starch is water-soluble. A plastic made of starch will deform when there is moisture, thereby limiting its use. This problem is solved by transforming starch into lactic acid by microorganisms. The lactic acid is then chemically treated to form long chains of poylmers, which bond together to form a plastic called polylactide (PLA).
Bacteria can also produce a bioplatic called polyhydroxyalkanoate (PHA), which can be simply harvested from the bacteria grown in culture. Scientists have transferred genes from these microbes to plants, too.
Currently, the focus of research is on production of programed-degradable plastics, so that we can control when and how they degrade to ensure that they hold up while they are still in use. For example, pots can be made of bioplastics that degrade once they are buried into the soil with the plant.
However, the cost of producing biodegradable plastics is 2 to 10 times higher than that for conventional plastics. Therefore, the use of bioplastics is not widespread enough to replace traditional plastics. In fact, to really help the environment, simply replacing old plastics with biodegradable plastcs does not work, because the landfill lacks oxygen and moisture that are needed to support the growth of the decomposer organisms.
Future research should focus on how to produce bioplastics in a cheaper way, so that traditional plastics can eventually be replaced. Strategies on how to collect these bioplastics in compost should also be investigated to maximize the degradability.