Page 30 - Plastics News August - 2023

A Better Approach to Biodegradation of Polymer Waste

to demonstrate this circular loop of
making polyester plastic, and not just
theorize that it could happen. They
went through the steps of first de-
grading samples to the starting mono-
mers and then re-forming a polyester
plastic. There is not enough informa-
tion available to assess its economic
viability they may well be applying for
patents as I write this but my initial re-
action is not too optimistic about this
arnessing enzymes to depolym- second, less-common approach uses being a commercially viable technol-
Herize waste polyester and re- biochemicals, specifically enzymes ogy. If you think about the “normal”
using the material to make new prod- made by “bugs,” to degrade the plas- recycling loop — make a product, sell
ucts has been shown to work. But is it tic. (Enzymes are protein-based cata- it, use it, retrieve it, and then repro-
economically viable? lysts that speed up a specific chemical cess it into a new product — these
There are hundreds of researchers fo- reaction without being consumed in degradation and repolymerization
cused on applying biological solutions it.) steps add another operation (or two).
to plastic waste. Their efforts can be Researchers at UT-Austin have had For what? The researchers started
divided into two approaches. The first some notable success with the sec- with PET and ended up with PET af-
uses “bugs” — microbes, fungi, and ond approach recently. They used terwards. What was gained? Or look-
so forth — to eat the plastic, while the synthetic biology to create an enzyme ing at it from another direction: What
second, less-common approach uses that degrades polyester back into its problem was solved? This is just add-
biochemicals, specifically enzymes starting materials. In other words, the ing extra steps.
made by “bugs,” to degrade the plas- enzymes are breaking the ester bond Except if I think about this a bit more,
tic. (Enzymes are protein-based cata- that makes polyester. The starting Post-consumer waste in the recycling
lysts that speed up a specific chemical chemicals can be recovered and then stream can be heavily contaminated
reaction without being consumed in turned back into new polyester. due to poor separation from other
it.) Enzymes tuned to specific chemi- recyclables, dirt, food, and other
Researchers at UT-Austin have had cal reactions contaminants. Because of this, I’ve al-
some notable success with the sec- This stands in stark contrast to the ways had high respect for recyclers.
ond approach recently. They used aforementioned first approach, which They’re dealing with a messy feed
synthetic biology to create an enzyme involves letting microbes and fungi de- that I’m glad I never had to. I’ve ex-
that degrades polyester back into its grade the material. Such degradation perienced plenty of bad days just try-
starting materials. In other words, the is not as controlled, and the result is a ing to process regrind, a feed stream
enzymes are breaking the ester bond seriously degraded product that isn’t that never left the plant. To try and
that makes polyester. The starting much good for anything else. This is work with whatever garbage is sent
chemicals can be recovered and then what happens to compostable plas- as recyclables scares me plenty. This
turned back into new polyester. tics — you get compost that can’t be technology might make that easier in
There are hundreds of researchers fo- turned into plastic. By contrast, en- the future.
cused on applying biological solutions zymes are tuned to specific chemical Since the enzymatic reaction is so
to plastic waste. Their efforts can be reactions and cannot influence any specific, it should be possible that it
divided into two approaches. The first other reactions. could find and degrade the polyester
uses “bugs” — microbes, fungi, and The researchers were actually able — and just the polyester — in a pile
so forth — to eat the plastic, while the of contaminated plastic.

30 PLASTICS NEWS August 2023
30 PLASTICS NEWS
August 2023