What are biodegradable polymers and are they the solution to our worsening climate situation?

There is a large stigma around plastic usage in everyday applications due to the rapid decline of our planet’s climate and increasing pollution of the atmosphere and oceans. The traditional plastics we all know are petroleum-based and made from crude oil (PET plastic). This means they are non-biodegradable and can remain in landfills for hundreds of years. What if we could replace the plastics we know and love with ecologically friendly and biodegradable plastic variants? 

You see, biodegradable plastics are made of the same components as normal non-biodegradable plastics, which are long chains of molecules called polymers. Biodegradable plastics and polymers aren’t anything new as we have known about naturally occurring biodegradable polymers or biopolymers and their applications for thousands of years. However, the application of synthetic polymers dates only some fifty years back and they were originally believed to be our saving grace in light of the Earth’s climate situation. However, the term ‘biodegradable polymers’ includes many different natural and synthetic biodegradable polymers, which also means very different real-world applications.

Natural biopolymers consist of proteins such as collagen, polysaccharides like cellulose, starch, and chitin, and even things like microbial polymers. Natural biopolymers have poor mechanical properties and their application commercially as food packaging is very limited. Starch based products suffer from water sensibility and applications of chitin are limited due to their insolubility. However, natural biopolymers have their applications in the biomedical fields. Proteins are the components of many tissues and they have been used extensively as biomaterials in absorbable sutures and tissue engineering. Chitin and its derivatives have been used as drug carriers, blood anticoagulants, and other biomedical applications. Products composed of starch polymers are used in wrapping plastics

This just goes to show that the everyday word ‘plastic’ is a lot more complex than one would originally imagine as there are thousands of these component polymers and thousands of different uses of these polymers. Plastic, and associatively polymers, nowadays seem to have a negative connotation because your brain automatically associates the word ‘plastic’ with the idea of non-biodegradable plastic waste overflowing in oceans and coastal regions. People are often unaware of the diversity of polymers and how dependent we are on them.

An example of a synthetic biodegradable plastic includes a plastic derived from antioxidant additives that degrade with the presence of UV rays. In the majority of cases, the polymer chain has a way or a component that facilitates the breaking down of the chain, allowing for better degradability of the plastic. However, it has always been difficult to find a biodegradable polymer that is strong enough to be used commercially and won’t degrade unexpectedly.

This is where aliphatic polyesters enter the scene. Aliphatic polyesters are essentially made from double bonded oxygen (ester) ring compounds that undergo ring opening polymerization to make long chain polymers. These compounds are biodegradable due to the characteristics of the chain backbone and because these aliphatic polyesters are quite long and dense they make for strong plastics. The most common and most extensively researched aliphatic polyester is polylactic acid or PLA because it is very cheap, has a high molecular weight, and is a biodegradable compound.

Synthetic degradable  polymers/polyesters sound like the perfect solution for plastic waste, so why aren’t we using them?

The thing is, we are using them and the results are disappointing.

Most degradable plastics still require high temperatures in order to begin degrading; temperatures which are not reached in waste dumps. This means we need to build specific waste disposal plants just to degrade these degradable plastics. This is a major problem when it comes to infrastructure because there simply aren’t enough plastic degradation sites to deal with the surge in bioplastic use. Not to mention, these plants cost a lot of money, which underdeveloped countries struggling most with plastic overflow cannot afford.

Some sources state that “if bioplastics end up in landfills, as many do, without enough oxygen to break them down, they can last for centuries and release methane, a potent greenhouse gas. If thrown into the environment, they pose threats similar to PET plastic.” This essentially defeats the whole purpose of having degradable plastics in the first place because these plastics will just remain in landfills regardless.

It is clear that even though the idea of a biodegradable coca-cola bottle sounds amazing, we must be careful with how exactly the plastic will behave in nature and how this affects the environment and ecosystems. As you can imagine, this requires further research and consideration. Most sources insist that rather than trying to substitute plastics for something more ecological, we should instead be aiming to just mitigate plastic use altogether and turn to true recyclable packaging solutions such as cardboard and cornstarch.

Written by Mikael Tiilikainen

Sources:

Robbins, Jim. “Why Bioplastics Will Not Solve the World’s Plastics Problem.” Yale E360, Yale School of the Environment, 31 Aug. 2020, https://e360.yale.edu/features/why-bioplastics-will-not-solve-the-worlds-plastics-problem.

“The Truth about Biodegradable Plastic Packaging.” Eventige, Eventige Media Group, 18 Jan. 2022, https://www.eventige.com/blog/biodegradable-plastic-packaging.

Vroman, Isabelle, and Lan Tighzert. “Biodegradable Polymers.” MDPI, Molecular Diversity Preservation International, 1 Apr. 2009, https://www.mdpi.com/1996-1944/2/2/307. 

One Reply to “What are biodegradable polymers and are they the solution to our worsening climate situation?”

  1. Miki – thanks for a super interesting blog post! I had wondered about this, since nowadays there is more and more biopolymer packaging, etc. – but sadly it seems that they aren’t the savior we may have hoped for :/
    -Edie

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