Removal of indoor air contaminants by wool carpet
- Polluted indoor air can lead to discomfort, reduced productivity of employees and even ill health.
- Research by AgResearch scientists has revealed that wool carpets significantly improve indoor air quality by rapidly absorbing the common pollutants formaldehyde, nitrogen oxides and sulphur dioxide.
- Not only does wool neutralise these contaminants more quickly and completely than synthetic carpet fibres, it does not re-emit them, even when heated. Wool carpet may continue purifying the air for up to 30 years.
Background
Indoor air pollution is the primary cause of Sick Building Syndrome and the associated discomfort, reduced productivity and increased instances of ill health. Indoor air quality is a public health concern that is receiving increasing attention because people are spending a higher proportion of their time indoors. The problem is exacerbated by the tendency for buildings to have air conditioning, which requires a semi-sealed environment to operate efficiently. This, in effect, traps the pollutants inside. Common indoor air pollutants associated with health hazards include formaldehyde, nitrogen oxides and sulphur dioxide. Formaldehyde can be introduced by emissions from certain building materials and furniture; while nitrogen oxides and sulphur dioxide are by-products of combustion processes (e.g. gas stoves and heaters).
Absorption of air contaminants by carpets
AgResearch and its predecessors the Wool Research Organisation of New Zealand (WRONZ) and Canesis have studied the potential of wool carpets to purify indoor air using specialised equipment and procedures. Our contract research for individual textile companies and wool grower organisations from around the world has provided them with valuable information that supports their promotional and product development strategies.
A comparison of different fibres showed that wool has better absorption than nylon, and that polyester had the least absorption. Wool carpet was found to reduce high levels (300 parts per million) of formaldehyde to virtually zero in four hours, whereas absorption was slower and less complete with nylon carpet. A low level of formaldehyde (5 parts per million) was reduced to near zero in 30 minutes by wool carpet, whereas even after an hour, nylon carpet had absorbed only 50%.
Hanks of wool carpet yarn suspended in a test chamber for 24 hours reduced the levels of nitrogen oxides from 300 to 5 parts per million, while nylon yarn reduced them to 60 ppm. The wool yarn also absorbed the gases appreciably faster, especially in the first 30 minutes, which suggests that wool carpet may provide an effective means for ameliorating sudden increases in levels of indoor contaminants. Similar studies by the Environmental and Medical Sciences Division of the UK Atomic Energy Research Establishment have shown that large amounts of sulphur dioxide are also irreversibly absorbed by wool carpets.
Effect of relative humidity
AgResearch scientists investigated how humidity affected the removal of air pollutants and found that absorption increased with increasing humidity and the rate and extent of gas absorption was higher for wool carpet than nylon carpet.
Re-emission and long-term performance
Wool carpets that had absorbed formaldehyde did not re-emit the formaldehyde, even when heated. Under similar conditions, re-emission from wool carpet that had absorbed high levels of nitrogen oxides was also negligible while nylon carpet re-emitted it more readily. Wool carpets are likely to be able to purify indoor air for up to 30 years. This is especially true for acidic gases (nitrogen oxides and sulphur dioxide) because of the high acid-combining potential of wool. Formaldehyde is known to react irreversibly with wool.