Is PLA biodegradable?


#1

So I got into a little argument with some friends on just how environmentally friendly PLA is.

I am coming from the angle that PLA is much better than plastic, as it is biodegradable, so while humans are still looking for a perfect plastic replacement, we can use PLA first for everyday needs, like straws and plastic bags. Not littering and correctly collect PLA waste for composting is important when it comes to being environmentally friendly, but there’s just no way to ensure people wouldn’t let the stuff go into the ocean, and I’d rather have PLA in the ocean than petroleum plastic.

My friends are saying that PLA being biodegradable is a myth, and Monsanto has gotten into all research papers claiming PLA is biodegradable. They say instead of being biodegradable, PLA at most breaks down into tiny plastic chunks that will end up in the marine life.

I went through some recent papers (published after 2017), and most of them say PLA can be degraded through hydrolysis. Water will break the ester bond and you will end up with the left over carbonyl group, when then can be metabolized by bacteria and the end product would be CO₂.

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Now, perhaps this process is slow. Not hundred-thousands of years slow like regular plastic, but 5 to 10 years slow in the ocean. It can be sped up with heat or being in a compost, but I’m mainly concerned about the stuff in the ocean. If it breaks up into tiny pieces and hasn’t yet been metabolized by bacteria, I can see how it could get ingested by marine animals.

So is PLA really biodegradable? Other than just saying no plastic, what’s a good alternative so that we don’t gunk up the ocean?

I mean all the papers I see seem positive…

https://www.omicsonline.org/proceedings/degradation-of-pla-in-a-simulated-marine-environment-after-600-days-69781.html


#2

Where did you get that five or ten year number from ?
I heard it needs a high temp and good oxygenation to degrade.


#3

There are two ways of breaking the ester chain. One is by applying heat, the other is by hydrolysis. It would work even better by applying both in an alkaline environment.

A lot of the criticism is that if PLA waste ends up in a landfill, even though there might be enough heat, but it would lack oxygen to actually facilitate the process. Although some say it would break down into methane.

In a compost, with heat, water, oxygen, and even help with some bacteria, PLA can be broken down. The issue is there aren’t enough PLA compost facilities around. There are none in Taiwan.


#4

It seems that PLA is not really helpful then.


#5

400 days
https://onlinelibrary.wiley.com/doi/full/10.1002/gch2.201700048

Another paper on this issue that put PLA in simulated sea water for 400 days. It is only difference between the previous paper that put PLA in sea water for 600 days is that the 600 days paper had actual marine life and bacteria in the water.

600 days
https://www.omicsonline.org/proceedings/degradation-of-pla-in-a-simulated-marine-environment-after-600-days-69781.html

The two paper ends up with completely different conclusions.


#6

The first paper is not written very well, I didn’t understand their conclusions. In the paper they say the PLGA is largely broken down but the conclusions seems to say it wasn’t.

Anyway 25c to simulate an ocean environment seems a little unrealistic.


#7

Omicsonline isn’t reputable. They pump out a lot of rubbish including conferences and journal links. They created their own journals. You just pay them to get your paper reviewed and published.
Myself and my colleagues avoid them.
Anything linking directly from there…I have a hard time trusting.


#8

And do you know any reliable sources in this topic, @Brianjones?
It would be interesting to see other related information.


#9

I know what isn’t reliable. Better journals would be a start.


#10

I didn’t mean to come across as doubting your statement.
It’s just that you sounded like someone who knows a bit about this subject, so it’ll would be good if you could share it with us.


#11

I just read some random stuff before because yes I have been involved in biodegradable biz. There is an incredible amount of bullshit and misleading lies in that industry.

One promising area was to create plastics that could be broken down in saline water. But I haven’t seen any good results from this yet.

Best biodegradables are wood and paper IMHO. We generally don’t need to reinvent the wheel. We know they break down and there are many microbes in soil and water just waiting to eat em up.

Best option is to avoid disposable plastics whenever possible. So eating on site, bringing your own containers, own utensils…

Interestingly some old plastics such as celluloid were also more degradable.

Certain plastics such as nylon are really hard to replace due to their properties. I can tell you about biodegradable toothbrushes and how many claims of the vendors are just lies.


#12

Surface water temperature around the Pacific garbage patch is around 21 to 24 degrees C currently, and can reach an average of 26 degrees during summer.

By the way, I just found out that the government shutdown also affected the NOAA website…


#13

From some sources, I get the impression that biodegradable plastic is a different beast from bioplastics. When they use the term biodegradable plastic, they mean petroleum based plastic that have stuff added to them to make them more “biodegradable”.

UN released a statement saying these types of biodegradable plastics don’t work.

The mechanism used sounds different from PLA and other aliphatic polyesters that have an ester bond that can be broken by hydrolysis.

While wood and paper are great, the issue is that usually plastic and bioplastics are used to be water proof for a while. Paper and wood containers often would require a plastic coating to make them more water resistant, but then we are back to square one with plastic waste.


#14

Yeah but what about the plastic that is not right at the surface ? That’s a bit of a gap there.


#15

maybe if something is weighing it down lower than 300m


#16

Im still on the fence but very curious about the true decomposing aspects in reality. Lab tests are generally very specific and bias. The 25c thing shines like a beacon of bias.

Seems if they just keep getting smaller over 10 years and manage to change structure at that point if everything went to the alchemists plans, there is still 10 years of constant consumption of said plastics and the whole point seems like a useless strategy unless we are also aiming to stop using it and/or evolve our technology to make something better.

Its like the clean energy debate, there is no answer yet but we have to support the cutting edge and allow more research to happen. So all these baby steps turn into tsunamis. In that reapect im all for these new plastics in hopes the research will create something great and revolutionary. Environmentalists tend to get too stuborn and write off the whole deal if it doesnt solve all the global problams yesterday. Thats not how stuff evolves.