Barbara Armstrong, of Cromwell, asks :-

Which is better for the environment: wool carpets or nylon carpets? (With the huge amount of television advertising spent on solution-dyed nylon carpets and with no carpet companies promoting woollen carpets one would almost think pure wool carpets are a thing of the past.)

Errol Wood, a fibre physicist well retired from the Wool Research Organisation of New Zealand, responded.

To address this question we must consider three aspects: The environmental footprint in manufacturing carpets, from fibre production to the finished product; The impact of carpets on our wellbeing indoors; The environmental costs of disposing of carpets at the end of their useful life.

Making carpets.

Wool carpets are made from a sustainable fibre produced with minimal impact on the environment. Nylon fibre is a by-product of the petroleum industry that has major, negative impact on the global environment and is not sustainable. Furthermore, wool is much more energy efficient because it uses less than 25% of the total energy required to produce nylon.

Once the fibres are made, the environmental differences between wool and nylon in making carpets are small. However, only wool must be scoured with detergent to remove grease and other contaminants, and large volumes of water are required. The scouring effluent must be disposed of in an environmentally-responsible way. Disposal issues also arise in treating effluent from the dyeing of both wool and nylon, however “solution-dyed” nylon avoids this problem because the colour is introduced into the fibre when it is formed.

Wool carpets are treated with an insecticide to prevent moths from eating them. While this treatment is seen as undermining wool’s “green credentials” there is no evidence that it affects human health. However, the effluent from the treatment is toxic to some aquatic life and must be properly treated before discharge.

Carpets and our well-being.

Our well-being is enhanced by installing a carpet in the home – we enjoy warmth, reduced noise, and increased comfort in standing, walking or sitting on it. Here it is the thickness and density of the carpet pile that is important rather than the type of fibre used. However, wool has a unique ability to absorb moisture, enabling a wool carpet to moderate the extremes of dryness and dampness indoors. To avoid people receiving static shocks from nylon carpets, manufacturers must include specially treated fibres while wool fibres conduct away static electricity naturally.

Polluted air can lead to discomfort and ill health amongst occupants of buildings, especially with the trend towards sealed, air-conditioned interiors. Research has shown that wool carpet absorbs formaldehyde, nitrogen dioxide and sulphur dioxide and can trap and hold these toxic gases for up to 30 years.

Carpet disposal.

Eventually a carpet will need to be replaced. Because of the large amounts of material involved, old carpets create problems in land-fills, and burning is not a good option. Recycling to make other useful products is the favoured disposal route.

Nylon carpets are easier to recycle because they are almost 100% synthetic. On the other hand, wool carpets are not 100% wool. They typically include a jute secondary backing, a polypropylene primary backing and latex adhesive. It is feasible to chop up old carpets and use the product as mulch for trees etc, providing an easy route for disposal. The wool breaks down and becomes a fertiliser while the other components degrade away.

Which is better? Take your pick.

Send questions to: Ask-A-Scientist, PO Box 31-035, Christchurch 8444 Or email: questions@ask-a-scientist.net