Sunday, October 04, 2009

Physical and chemical structure of Australian Merino that make it naturally more odour reducing than other textiles.



There are a number of aspects of the physical and chemical structure of Australian Merino that make it naturally more odour reducing than other textiles.

Moisture transport

While sweat itself has no odour, if it remains on the skin in time bacteria develop and create unpleasant body odours. Merino reduces the opportunity for odours to generate because it is more efficient than other textiles at absorbing sweat and evaporating it into the air.

No microbial attraction

Odour Resistance. Bacteria are more attracted to the positively charged smooth synthetic fibre than the scaly neutral Merino.Studies have shown that bacteria are more attracted to the smooth, positively charged surface of a synthetic fibre than the scaly surface of a Merino fibre which carries no charge. (Fig 1)

Moisture absorption

The Merino has a much greater capacity than other fibres to absorb moisture. In fact, it can absorb 35% of its own weight in liquid. The moisture is bound within the structure, and so is not available to microbes, which are unable to penetrate the scaly surface of the fibre.

Fatty acids

The very outer layer of the epicuticle has a high concentration of fatty acids, which are considered to have anti-bacterial properties.

Odour binding

The Merino fibre has a complex internal chemistry that potentially allows it to bind the acidic, basic and sulphurous odours that are components of body odour.

Glass transition

In water and conditions of high humidity, Merino passes through what is termed a glass transition at which point it dramatically increases its rate of absorption and desorption.

Trapping odours

Once past this glass transition, the rate of diffusion of small and large molecules into the fibre increases and it is able to absorb odours faster. When the temperature drops, and the fibre once again falls below the glass transition, the odours are trapped within the structure even if the moisture evaporates. Later, during laundering, the garment again passes through the glass transition point and the odours are carried out of the structure by the water. Synthetics aren’t able to benefit from this same effect because they do not pass through glass transition during normal wear.

Trial preference

Fig 2 - Sock Preference. In trials merino socks were preferred to cottonIn trials, fifteen users were asked to wear socks made from four different textiles and indicate their preference on the basis of odour strength both after wear and after washing. Merino socks were the preferred option in both cases, winning out narrowly over cotton but by significant margins over acrylic and polypropylene. (Fig 2)

Summary

The physical and chemical properties of the Merino fibre makes it naturally reduce odour, which is why in trials users show a preference for socks made of Merino, rather than those made of other textiles.

Sources

  • John D. Leeder, 1984, Wool – Nature’s Wonder Fibre, Ocean Grove, Vic.: Australasian Textile Publishers and J.D. Leeder
  • Comfort Advantages of Wool Socks. IWS publication
    Johnson, N.A.G. et al, (2003)
  • Wool as a Technical Fibre, in J. Text. Inst., V. 94 Part 3, pp.26-41.
All figures and tables courtesy of CSIRO unless otherwise noted.

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