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AGRICULTURAL MULCH FILM
Farmers all over the world spread thousands of square kilometres of plastic sheet on their fields to protect their crop from weeds and to reduce the evaporation of water. Essentially, farmers have three options:
- Conventional plastic – after the harvest the farmer has to drag hectares of plastic off his fields. He is not allowed to burn it on the farm, and burying it is not a good idea because it is labour-intensive and effectively puts the site out of cultivation, so he has to pay for it to be taken away. Some farmers send their plastic for recycling but it is usually contaminated with mud and other contaminants, so recycling does not make a lot of sense in economic or environmental terms when you consider the cost of hauling the plastic off the field, loading a large truck, and driving it along country roads to a recycling facility often hundreds of miles away – using fossil fuels, causing congestion, and emitting pollution. The plastic then has to be washed and the contamination has to be disposed of – and then the plastic has to be processed into recyclate.
Also, having lain on the fields exposed to sunlight it is likely to have degraded to the point that it is not fit for recycling, and fragments will have been scattered by the wind whilst being removed. The UK Environment Minister said on 25th May 2023 that “the government does not hold data on the amount of agri-plastic film collected or recycled.”
- Bio-based Plastic – this is expensive and may not be strong enough to resist tearing. The timescale for degradation cannot be programmed.
- Oxo-biodegradable plastic – successful field-trials have been run in Wales. The next time the field is ploughed, the biodegradable material will be returned to the soil, where it will be bioassimilated by the bacteria and will provide a source of carbon for next year’s plants.
By taking note of the climatic conditions in the area, and using the correct formulation, it is possible to make the plastic last for as long or short a time the farmer requires.
It is no more difficult to spread d2w plastic on the fields than ordinary plastic.
Oxo-biodegradable mulch films have been studied by scientists for more than 20 years. At page 47 of Degradable Polymers, Principles and Applications[1] Professor Scott says “The degradation products formed by oxo-biodegradation are of benefit to the agricultural environment as biomass and ultimately in the form of humus. Carbon is retained in the soil during oxo-biodegradation in a form accessible to growing plants, rather than by being emitted to the environment as carbon dioxide, as is the case with hydro-biodegradable polymers (e.g. pure cellulose and starch) ….. Time control of biodegradation of the synthetic carbon-chain polymers is achieved by antioxidants that behave similarly to naturally occurring antioxidants present in lignin and tannin.”
With regard to the edges of the mulch film which are buried to hold it in place. They will still biodegrade because, unlike photo-degradable plastic, an oxo-biodegradable plastic does not need constant exposure to sunlight. It is also possible to make a mulch film in which the buried sides of the film incorporate a different biodegradable masterbatch as compared to the middle part of the film.
[1] (ISBN 1-4020-0790-6) See also “Polymers and the Environment” (ISBN 10: 0-85404-578-3) pages 109-118 and 461-466, and www.biodeg.org/wp-content/uploads/2023/07/Scott-Wiles-paper-June-2001.pdf page 618.
