Plastics are comprised of large molecules called “polymers” (“poly-” is Greek for “many”). Polymers are long chain molecules made of smaller, repeating unit molecules called “monomers” (“mono-” is Greek for “one”), similar to how beads (monomers) connected together form a necklace (polymer). Naturally occurring polymers include DNA, starch, wood and natural rubber. The two synthetic polymers produced on the largest scale are polyethylene and polypropylene, but there are many different kinds of synthetic polymers and plastics.
A sustainable polymer is a plastic material that addresses the needs of consumers without damaging our environment, health, and economy. To do this, researchers are working to develop polymers that, when compared with their non-sustainable counterparts:
- use renewable feedstocks, such as plants, for production
- use less net water and non-renewable energy in production
- emit less greenhouse gases during production
- produce less waste in production
- have a smaller carbon-footprint
- have a facile end life
How are sustainable plastics different from ordinary plastics?
1. Petroleum or natural gas is converted into chemicals (monomers).
2. These monomers are made into useful plastic products.
3. The plastic products can be incinerated, recycled, or thrown away.
For more information about the petroleum-based plastic life cycle see The American Chemical Society’s “Life Cycle of a Plastic Product,” and Ellen MacArthur Foundation infographic on the linearity of the plastic lifecycle.
1. Carbon dioxide and water are used in photosynthesis to grow plants
2. The plants are harvested and processed to make chemicals (monomers or polymers):
The plant material may be fermented to produce monomers (e.g., plant-derived sugar to lactic acid)
Chemicals may be extracted from the plant to make monomers (e.g., modified soybean oil used in polyurethane foam) or polymers (e.g natural rubber or polyhydroxyalkanoates)
Through bioengineering and microbial pathways, plant-derived sugars or other molecules can be converted into monomers.
3. The renewable chemicals are converted to plastic products.
4. Some sustainable polymers can be composted in addition to being recycle or incinerated to recover their energy content.
5. Composting produces carbon dioxide, water and organic matter (dirt) which is used to regenerate the renewable resource feedstock (plants).
What new policies are needed?
Sustainable polymers are relatively new to the consumer market. Therefore, there is much work to be done in terms of developing appropriate policies. Currently, there is inadequate regulation of advertising and labeling of environmentally-friendly products. More policies are needed to prevent “greenwashing” that can mislead consumers. In order to take full advantage of the properties of compostable polymers, industrial composting should be more accessible to consumers, possibly through the use of curbside compost pick-up. Finally, progress towards improved sustainable polymers can only result from scientific research and technological innovation, which requires public support and a commitment to research and education.