Sustainable Polymers 101

What is sustainability?

Sustainability has many definitions. One way to think of it is:

“Meeting the needs of the present without compromising the ability of future generations to meet their needs.”

This definition was created in: Our Common Future, Report of the World Commission on Environment and Development, World Commission on Environment and Development, 1987. Published as Annex to General Assembly document A/42/427, Development and International Co-operation: Environment August 2, 1987.

What is a polymer?

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.

For more information about polymers visit the Macrogalleria or view this Polymers Crash Course video.

What is a sustainable polymer?

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 plants are sustainable polymers made from?

Currently, commercially produced sustainable polymers are made from starch-containing plants like corn or sugarcane and seed oils such as soybean or other vegetable oils. Scientists around the world are studying ways to make polymers from non-food source materials, such as trees (lignin), switchgrass, and agricultural waste products like corn stover.

Are sustainable polymers more environmentally friendly to produce?

Yes. Ideally a sustainable polymer should be more environmentally friendly to make than its petroleum-derived counterpart. This would mean it required less water and non-renewable energy to make, and it would have less pollution emissions, when compared with its petroleum-based counterpart. However, these measurements are complex, and many companies go through extensive life-cycle analysis processes to determine this. 

See the NatureWorks Environmental Benefits Calculator to compare a common sustainable polymer, PLA, to petroleum-derived polymers or read more about the life cycle analysis comparisons between sustainable plastics and petroleum-derived plastics

What products can be made from sustainable polymers?

Sustainable polymers comprise a growing segment in the market. Currently, polylactide, derived from corn, is made into plastic cutlery, food containers, fibers for clothing, and even cell phone cases. Modified soybean oil is used right now to make polyurethane foam for products like seating cushions and memory foam pillows. The list of products will grow as more research is done and further sustainable polymers are developed.

What are the challenges of sustainable polymers?

Some of the challenges facing sustainable polymers include obtaining physical properties (such as toughness, melting temperature, color, and elasticity) that rival traditional polymers while remaining cost competitive. Extensive research is currently going on in universities and companies worldwide to improve the properties of sustainable polymers.

Are sustainable polymers edible?

No, sustainable polymers are not edible. Although they are derived from plants, sustainable polymers do not provide any nutritive value and will act like any other plastic when ingested.

Are sustainable polymers recyclable?

The most commercially available sustainable polymer is PLA. This cannot currently be recycled, and should be separated in the recycling stream. See below for information on composting of PLA. For more information about developing sorting technologies, see NatureWorks page on developing near infrared PLA sorting technologies.

Other sustainable polymers can be recycled through chemical recycling processes, but it is unlikely that the average consumer will encounter these materials in their daily life.

Will sustainable polymers degrade on the shelf, in a landfill, or outside on the ground?

Sustainable polymers are designed to last while you use the product. They will not degrade on a shelf or in your home if used properly. Preliminary tests indicate that sustainable polymers will not biodegrade in a landfill due to insufficient conditions (such as low temperatures and lack of oxygen). Sustainable polymers will also not degrade outside on the ground, so you should always dispose of your plastic waste correctly.

Can sustainable polymers be composted?

Sustainable polymers that are marked with a seal from the US Composting Council can be composted in industrial compost facilities. Backyard compost heaps typically do not get hot enough or provide sufficient oxygen for these plastics to break down.

For more detailed information, see the World Centric page on compostable plastics.

To find an industrial composter near you visit Find A Composter.

How can I tell if a product is made from sustainable polymers?

Unfortunately, right now it is not easy to tell if a product is made from sustainable polymers. Part of the problem is that there isn’t a universally accepted definition of sustainable with respect to materials. However, there are certifications for compostability and biobased content which can help you to identify which products are truly more environmentally friendly. Some of the trade names of different sustainable and partially sustainable polymers are: Ingeo, Mirel, BiOH, Mater-Bi, and Sorona. Additionally, certified compostable plastics will be marked with a compost seal.

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.