Clarification required regarding compostable plastics.

Oil-based plastic films are not edible by micro-organisms, so when left as litter does not degrade. In contrast plastic plant-based films classified as compostable break down in contact with the soil, in what is a low temperature rotting process. These break down over 6-8 months in my garden composter.

Materials classified as biodegradable need to be treated in an industrial composting process, with temperatures rising to 70°C. The result is a compost crumb structure, suitable for spreading on land as a fertiliser. They may or may not decompose at lower temperatures.

Oxy, oil-based plastic materials, have a light sensitive chemical in them, which causes the film to break into small fragments of material, which will not subsequently degrade.

For compostable or biodegradable films to break down, the microbes need a blended mix of protein, minerals, carbohydrates, air and moisture. Optimally films need to be shredded and mixed with food or garden waste to speed digestion by microbes.

As compostable films become the norm for food packaging, more attention will have to be paid to ensure the compost caddy contains a waste mixture that suits micro-organisms’ digestive needs.

If plant-based and oil-based films are not clearly differentiated, the default action must be to put the film in the residual waste bin.

When we realise that plant-based films are not only plastic substitutes but are in fact food, we can start sending such material to anaerobic digesters to produce biogas to substitute for CO₂ producing natural gas.