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The South African and international mohair industry may soon benefit from a novel project of the CSIR to develop a device to measure the lustre of this elite fibre.
South Africa currently produces more than 60% of the total world production of mohair. The silk-like natural fibres are from the hair of the Angora goat and can be woven or spun into plush fabric.
Lustre, one of the most important characteristics of mohair, distinguishes it from all other animal fibres of similar fineness. One of the quality attributes associated with South African mohair is its excellent lustre properties. The lustre that differentiates mohair is largely due to its relatively smooth surface, resulting from its relatively thin and long scales.
According to Dr Anton Botha, senior fibres and textiles researcher of CSIR Materials Science and Manufacturing, no practical acceptable method of measuring mohair lustre exists. Lustre of mohair is still being assessed entirely subjectively. A cost-effective method would be extremely valuable to the entire mohair industry, i.e. angora goat breeders, mohair traders and buyers, mohair processors and mohair users. It would greatly enhance the quality image of South African mohair and place it at the forefront of mohair objective measurement worldwide. It will also provide breeders with an objective tool whereby they can either breed for better lustre of at least avoid sacrificing lustre when breeding for other desirable characteristics, such as fineness. There has been an increasing demand, and premium price paid, for finer mohair. However, the perception exists that the increased fineness is at the expense of lustre.
The CSIR has been conducting collaborative and innovative research to enhance the competitive capabilities of the South African textile and clothing industries. The fibres and textile technology area focuses on fibres, textiles and clothing, using emerging technologies, such as nanotechnology, biotechnology, as well as polymer and natural fibre composite technologies.
Current research on mohair concentrates on measuring the surface characteristics (surface roughness, scale definition and density) of the mohair fibres and relating these measurement values to lustre. "If these results prove promising, then an instrument could be developed, probably based on high-resolution image analyses for rapidly measuring surface characteristics, possibly at the same time as diameter," he says.
Considering the natural variability that occurs within and between mohair fleeces, a practical, preferably 'on-farm', method for measuring lustre would need to be based on the relatively rapid and sufficiently accurate measurement of a cluster (group or staple) of fibres, either in greasy or scoured state. It would also need to measure lustre independent of other mohair characteristics, such as the colour and fineness.
Lustre relates to the manner in which light is reflected from the fibre surfaces. Light falling on a fibre surface can either be transmitted through, or absorbed by, the surface, or it can be reflected from it. Depending on the surface, the light can be reflected in two ways - the surface can be such that the angle of the reflection of the light rays is equal to the angle of incidence (this is known as mirror or specular reflectance) or the light can be scattered in many directions through a number of angles of reflectance. This is known as diffuse or scattered reflection. In practice, reflected light comprises both specular and diffuse components, the higher proportion of the former, the greater the lustre. Lustre is directly related to the intensity of specular reflection from the mohair fibre surface. Compared with other keratin fibres, light reflected from mohair fibres contains a high percentage of specularly reflected light, which is due largely to its relatively smooth surface.
Very little work of practical significance has been carried out on mohair lustre, although a considerable amount of research has been done on the measurement of the lustre of human hair, using highly sophisticated and expensive goniophotometric techniques. Such techniques are, however, inappropriate and impractical for routine measurement of the lustre of mohair fibres. Goniophotometric tests are typically carried out on single fibres, necessitating a number of tests (fibres) per sample, which make these very time-consuming and expensive. The goniophotometric values for lustre are generally regarded as the benchmark for all other measurement techniques and currently the only recognised method for measuring the lustre of human hair and fibres.
During the past year much time was devoted to the sourcing of a wide range of samples and assessing lustre and measurements. This was necessary to obtain a set of mohair samples that differed independently in terms of lustre and diameter and that was not too numerous for measurement purposes. Several measurement techniques were also performed on the samples for initial screening purposes.
"Several research technology areas in the CSIR are now joining forces with national and international universities and will collaborate on this project," says Botha. "It is a novel project that could benefit the entire mohair industry across the value-chain."
Contact detail: Dr Anton Botha, email abotha@csir.co.za.
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