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?
Traditional
Polymers:
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.
Sustainable
Polymers:
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.
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