Biodegradable Polymers

Subject: Performance of PLA vs. PET and PS

This memo is in regards to a study comparing the properties of commonly used petroleum based polymers (PS and PET) with a biodegradable alternative (PLA). The study found that PLA has several properties in common with these petroleum based plastics. It also proposes further studies on PLA polymers to better determine their performance and compatibility in the world of food packaging.

Why do we Need to Change?

The U.S. has been steadily increasing its production of municipal solid waste (MSW). In 2003, packaging represented 31.7% of America’s 236 million tons of MSW [1]. Approximately 6.35 million tons of plastic goods were taking up landfill space in 2003 [1]. These numbers all seem to be on the rise. Biodegradable polymers are an attempt to decrease America’s dependence on landfills for disposing of their packaging waste. A drastic reduction in the amount of packaging waste in landfills would be a good step toward the overall reduction of MSW. Composting is beginning to take precedence over traditional recycling programs throughout the U.S. Composting does not take as much effort to accomplish as sorting and reprocessing for recycling do. Composting recovered 7.1% of the MSW in 2003 [1].

Is PLA the answer?

The best thing about PLA is that it is produced from renewable resources. It is primarily produced by the fermentation of corn dextrose, thus providing significant energy savings in comparison to synthetic polymers [2]. PLA can also be recyclable and compostable [3]. Its physical and mechanical properties can be easily manipulated through the architecture (by changing the levels of L, D, or meso-lactide) or by changing the molecular mass [3]. PLA can be processed through many traditional methods including injection molding, sheet extrusion, and thermoforming. PLA has also been approved by the Food and Drug Administration (FDA) for contact with food in food packaging applications [4].

After testing these three polymers, it is safe to say that PLA is comparable to the petroleum based polymers in a number of applications. PLA was in the middle or at the top of most of these test results. At ambient conditions, PLA exhibited an impact resistance greater than PS. PLA also has a lower oxygen permeability coefficient than PS. PLA has the best modulus of elasticity of the three. These results bring hope for the future of PLA as an alternative to synthetic polymers, but there is still a lot research to be done to ensure quality. These PLA products need to be tested