Bioplastics
This article was originally posted in another forum in Jan 2020.
I read an article by the BBC's environment analyst, Roger Harrabin, entitled "Plastic packaging ban 'could harm environment'". This is well worth reading, not least because it seems to go against accepted folk wisdom. Harrabin quotes a spokesperson from the Green Alliance (whoever they are) who says "over 80% of consumers think biodegradable or compostable plastic is environmentally friendly, but there is little understanding of what the terms mean and how the material should be dealt with". I'm one of those consumers so I will dig a bit deeper into composting (apologies) and what 'bioplastic' and 'biodegradable' actually mean. I found an excellent review in Ensia:
ARE BIOPLASTICS BETTER FOR THE ENVIRONMENT THAN CONVENTIONAL PLASTICS?
Confusion among terms like bioplastics, bio-based and biodegradable plastics makes it hard to discern — and make — the environmentally responsible choice.
I recommend you read this for yourself, but in a nutshell it says:
- the term "bioplastics" covers both plastics made at least in part from plant (or biological) matter and biodegradable plastics
- not all plastics made from plants are biodegradable. Not all biodegradable plastics are made from plants
- some plastics made from plants are chemically identical to plastics made from fossil fuel and they behave the same way in the environment
- oxo-biodegradable plastics are conventional plastics mixed with metal compounds that make them fall apart faster. There is no obvious environmental benefit from doing this
- there are things called "enzyme-mediated degradable plastics" which are not truly biodegradable ("truly biodegradable" means I think that microbes will eat it).
For example polylactic acid (PLA) is made from plants. It is used by Vegware (they use other materials as well) and it is recyclable, biodegradable, and compostable. It doesn't biodegrade easily though, and doesn't seem to degrade at all in seawater - it needs temperatures of 58 degrees C and up, which means an industrial composter. (This article doesn't say if it will biodegrade if it ends up inside a whale.) Other plastics such as PHAs degrade nicely in the tropics but more slowly in the Med and much more slowly in cold water.
In-Vessel Composters (IVCs) can easily get to 58 degrees, but many commercial composters use open windrows, which as far as I can tell are just a garden compost heap scaled up and managed properly. I don't know how hot it is in the middle of a windrow. In UK catering waste has to go to IVCs or anaerobic digesters (ADs). There can be benefits in using compostable plastics bags for food waste, but as the sorting machines used by ADs can't distinguish between them and conventional plastic they are likely to be screened out and sent to incineration. (Where I live all the food waste goes to incineration anyway.)
Vegware says that its products break down "in industrial composting facilities" in under 12 weeks. Suez (who actually do the composting) put food waste into an IVC to two days at 60 degrees and then leave it in windrows for up to 10 weeks. Presumably that's enough to degrade PLA but I'm not sure. After 10 weeks the material is screened so any remaining lumps of plastic would be dumped.
Although the Ensia article aims to help us make the environmentally responsible choice, it's still not clear to me what that is.
See also:
van der Zee, M., & Molenveld, K. (2020). The fate of (compostable) plastic products in a full scale industrial organic waste treatment facility. (Report / Wageningen Food & Biobased Research; No. 2020). Wageningen: Wageningen Food & Biobased Research.
There is an EU standard for compostable plastic, EN 13432.