IWTO is often asked, "Is wool is biodegradable?" In a word, "Yes" – and here's how.
The Keratin Component
Wool grows naturally on sheep, and is made of a protein called keratin – the same protein that is in human hair. When exposed to moisture for prolonged periods, for example in soil or compost, wool fibre will readily decompose. The warmer and wetter the conditions, the faster the breakdown. Bacteria and fungi break down the wool. The fungi first destroy the ends of the wool fibre, and bacteria then digest the weakened fibre by secreting enzymes.
A wide range of fungi and bacteria are involved, including:
Fungi: Microsporum, Trichophton, Fuasarium, Rhizopus, Chaetomium, Aspergillius and Penicillium
Bacteria: Actinomycetes, Streptomyces, Pseudomonas, Proteus, Bacillus
A soil burial study undertaken by AgResearch showed that 10 wool fabrics (knitted and woven) lost 95% of their weight on average over 15 weeks. Some finishes or treatments may slow the process down. See The Feasibility of Large-Scale Composting of Waste Wool in Green Fashion vol. 1, by Hustvedt, G., Meier, E., and Waliczek, T. (Springer Singapore, 2016, pp 95-107).
Equally Important, Nitrogen
Wool contains a high percentage of nitrogen. This high nitrogen content is the reason wool biodegrades so well. It also makes wool a good "slow-release"fertiliser.
How Long Does it Take?
The rate of breakdown is very much determined by the environment. If we look at composting, for example, the answer will depend upon how the composting is done. What has been added to the wool? What are the proportions of the mix? What is the temperature and the pH balance of the soil? Loose wool will biodegrade at a different rate from that of a wool garment.
Tests show that with the ideal conditions wool products are almost completely degraded after six months in the ground. Seams may not degrade as easily as the rest of a garment, because they consist of a double (hence thicker) layer of fabric and are often sewn with polyester thread. The dyes used on a wool product do not impact the results. (And chrome dye treatments, which might impact results, are now very rarely used.)
Conversely, clean dry wool fibres do not easily biodegrade, due to wool's unique chemical make-up – which is why you sometimes hear about ancient wool clothes being found in archeoloigical sites or on mummies such as Cherchen Man.
Why is biodegradability important?
Products that are biodegradable are part of a natural cycle. They come from nature and go back to nature, enriching the soil and nourishing new life. In the UK alone, around 350,000 tonnes of used clothing and 370,000 tonnes of carpets go to landfill every year. The numbers are similar for other developed countries. Products made out of synthetic fibres can take 30-40 years to degrade, contributing to the ever-increasing piles of waste in landfills.
Because it naturally degrades in a fraction of that time, wool is the obvious choice for anyone concerned about the health of our planet.
For more information on biodegradability access the IWTO Wool & Biodegradability Fact Sheet.