Bags Biodegradation & Composting Michael Stephen Column PLA

Timescale for biodegradation, Paper Bags, PLA (FREE)

Today Michael talks about Timescale for biodegradation; and about Paper and PLA. This is a FREE article


I am often asked about timescale for biodegradation of plastics. The answer depends on the type of plastic.

Plastic marketed as compostable has to biodegrade within 180 days, because that is the timescale that industrial composters require to fit in with their own timescale for composting garden waste and other vegetable material.  However, plastic does not convert into compost – it is required by EN13432 and ASTM D6400 to convert into CO2 – and many industrial composters will not accept plastic of any kind in their facility.  As mentioned in my column last week, the city of Ann Arbor, Michigan will no longer accept plastic bags in its composting facilities, and Marin County in California has also now decided to ban the type of plastic marketed as compostable.  See Composting  Also, when this type of plastic gets into a recycling waste stream it contaminates it and makes the whole batch useless.

Ordinary Plastic (PE and PP)   This will fragment into microplastics quite rapidly on exposure to sunlight, but its molecular weight is too high to be accessible to microbes. It can therefore lie or float around for many decades before it eventually biodegrades.  This is the characteristic of plastic which has caused so much public concern, and generates demands for it to be banned or taxed, and it is for this reason that oxo-biodegradable plastic was invented.

Oxo-biodegradable plastic.  This is ordinary PE or PP, upgraded with a catalyst such as d2w to accelerate oxidation and reduce the molecular weight to the point where the microbes can biodegrade it and recycle it back into nature.  Timescale depends on how much heat or sunlight it receives, but it will still biodegrade very much more quickly than ordinary plastic in any location in the open environment – even in cool, dark conditions.  (Queen Mary University London have estimated 90 times quicker).  It could be made to biodegrade even more quickly, but there would be no point in that, as a plastic product must have a reasonable service-life. There is no need to fit in with the short timescales required by the industrial composters (who don’t want plastic anyway See Composting  ), and there is an important environmental benefit because it biodegrades significantly faster than ordinary plastic.


The Daily Mail (Australia) reported on 31st October that a furious shopper has vented her anger at Coles supermarket for switching away from plastic bags – showing how her groceries were damaged when one of the new paper bags gave way.

The supermarket giant, along with rival Woolworths, phased out soft-plastic shopping bags in June 2023, citing environmental reasons, and  Marks & Spencer in the UK have done the same.

The shopper had packed her groceries in Coles’ new 25c brown paper bags designed to hold up to 6kg, but the bottom soon fell out.  Footage showed groceries and the receipt strewn across the ground.

She also claimed she won’t be the first or last shopper to see their grocery bags fall apart. ‘Plenty of others have had the same problem. If the bags aren’t fit for purpose and can’t hold the 6kgs that they claim, they shouldn’t be sold,’ she said.

She is right.  It was a mistake to demonise plastic carry bags, which were much stronger, even when wet.  All that was necessary was to make them oxo-biodegradable so that they would not create microplastics and accumulate if they got into the open environment.


I noticed this on Linkedin last week “According to latest report, we have been greenwashed by the Paper industry for too long”:

  • Paper-based packaging: largest source of packaging waste in Europe (41%), more than the total of the two next largest sources (plastics 19%, glass 19%)
  • Brutal deforestation & biodiversity/water scarcity loss: paper responsible for about 35% of all clear-felled trees .  Every year 3 billion trees are cut down globally for paper-based packaging
  • Last 20yrs, Brazil tripled its pulp production, now covering an area of 7.2mha – (the size of Belgium). Eucalyptus & pine plantations in Brazil exacerbating water scarcity, forest fires and biodiversity loss.
  • Finnish forests now a net emitter of carbon due to overlogging. Capacity of Swedish forests to capture CO2 reduced by 5 million tonnes as result of over exploitation
  • Pulp and paper industry: world’s third largest consumer of water.  Production of one A4 sheet of paper requires around 10L of water. World’s fifth largest consumer of energy –
  • Little more than 50% of the paper and board produced uses recovered fibre. The remainder are made of virgin fibres.
  • In theory, paper and cardboard can be recycled around eight times but on average European paper fibres are only recycled 3.5 times 
  • Paper-based food packaging is usually combined with plastics or other chemical coatings or aluminium, hardly recyclable
  • – Paper packaging alternatives to plastic solutions do not contribute to reduction in carbon emissions, on the contrary, they increase climate change and resource depletion.


  • not an environmentally friendly option to ordinary plastic

This is the conclusion of a scientific study at the University of Gothenburg Chronic poly(l-lactide) (PLA)- microplastic ingestion affects social behavior of juvenile European perch (Perca fluviatilis)

“We see that PLA is not harmless to fish, so it should not be sold as an environmentally friendly alternative to ordinary plastic. It should be considered as equivalent to ordinary plastic,”

Michael Stephen

Michael Stephen is a lawyer and was a member of the United Kingdom Parliament, where he served on the Environment Select Committee. When he left Parliament Symphony Environmental Technologies Plc. attracted his attention because of his interest in the environment. He is now Deputy Chairman of Symphony, which is listed on the AIM market of the London Stock Exchange, and is the founder and Chairman of the Biodegradable Plastics Association.

Earlier Postings in this Column

All articles from Michael Stephen

Interview with Michael Stephen

Questions and Answers on OXO-Biodegradability


The opinions expressed here by Michael Stephen and other columnists are their own, not those of

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