Last update: March 30, 2012 03:23:51 PM E-mail Print

 

Difference between good and poor quality wool

 

J.J. Venter. Agricultural Researcher

Animal Production. Karoo Region

P.B. X529. Middelburg. C.P. 5900

 

 

It is endeavoured through sustained research to improve the quality of Merino wool to ensure its demand by the wool trade and to suit the requirements of the manufacturers.

According to the classing standards for Merino wool prescribed by the National Wool Growers' Association of South Africa (1978), quality means the definition and evenness of crimp, the handle and the presence or absence of deviating fibres.

Quality is basically associated with trueness of breeding, i.e. uniformity of fibre thickness in wool, and indicates the usefulness of wool as a textile fibre.

Three grades of quality are made, namely:

 

Good quality

showing a well-defined and regular crimp, a kind handle and the absence of deviating fibres in wool.

 

Fair quality

having an irregular or indistinct crimp or a dull appearance, a slight lack in handle and indication of deviating fibres.

 

Poor quality

also called common wool- clearly showing a lack of definition or regularity of crimp, a harsh handle and/ or presence of noticeably coarse fibres or hair in the wool.

 

In Merino wool production the handle of wool is considered as an indication of quality (character). Preference is given to softness of handle in the judgement of wool and selection of sheep which produce a wool of good quality.

Factors which may influence the stiffness of the wool and so indirectly the handle and thus the assessment of the quality will contribute to a marked difference in the physical properties of wool of either good or poor quality.

Since it is essential to produce a wool of good textile properties, an investigation was made to identify measurable differences in the physical properties of wool of Merino sheep purposely selected and bred for wool of either good or poor quality.

For nine successive years (1969 to 1977) midrib wool samples were taken from the two-tooth ewe and ram progeny. The quality of the wool was subjectively assessed and points were awarded according to grade: a wool of good quality received 4 to 5 points while a wool of poor quality received 1 to 2 points. Wool samples were analysed for the following properties: fibre diameter, crimp frequency, fibre length, crimp ratio, compressibility, feltability and degree of weathering.

A marked difference between wool of good and poor quality was apparent in respect of almost all properties. The difference between the wool of ewes and rams was inconsistent at the age of two-tooth (18 months). In some cases the differences were relatively small and not clear.

The wool of good quality was significantly finer, by one to two micronmetres, and had fewer crimps per 25,4mm than normal for fine wool and was longer than wool of poor quality. Wool of good quality was consequently much more under-crimped and had a significantly lower resistance to compression and a higher feltability. It was also significantly more weathered in the tip portion.

A gradual decline in resistance to compression and an increase in felting propensity were noted over the nine years of purposeful selection for good quality wool. Softness of handle, which is considered a requisite for quality, is associated with a fine fibre or a low resistance to compression. This is confirmed by this study, from which it was evident that wool of good quality with its characteristic so-called "kind-handle" was significantly finer and less crimped than wool of poor quality.

It was further obvious that purposeful selection and breeding of good quality, indirectly emphasizing softness of handle, cause the wool to become more under-crimped, resulting in a reduction in resistance to compression and an increase in feltability. Such wool will also tend to be flabby and lack substance on the sheep's back, where it may fall open more easily, especially when it is long during the hot summer months, and may become more deeply weathered.

Too much stress on quality may also lead to a deterioration in staple formation, fleece density and percentage of yolk.

It was evident that wool of poor quality, in contrast to that of good quality, deviated less from the Duerden-relationship. It tended to maintain a relative average value in respect of resistance to compression and felting propensity, and also was less subject to weathering deeper into the staple.

Highly crimped wools, having a high resistance to compression, are very suitable for various purposes. Selection for a high resistance to compression must, however, is applied with caution in formulating breeding plans, owing to its genetic responses by changing the balance of the parameters relating to wool production.  With an increase in quality number, normally crimped wools (according to Duerden's Standards) showed only a slight increase in resistance to compression, as well as In resistance to extension of individual crimped fibres, which may be ignored for all practical purposes. Fine and coarse Duerden-true Merino wools may thus have the same handle and also generally perform better in processing that either under-crimped or over-crimped wools of corresponding diameters.

Evidently Duerden-true wools also generally showed certain desirable properties in the end product, like good draping quality, high crease resistance and less shrinkage. Selection and breeding of a Duerden-true wool, therefore, is strongly recommended in order to retain the desirable properties.

A more detailed description of good quality wool should include the following terms: well defined, evenly crimped in relation to fibre diameter and showing no hairlike. fibres (thick fibres, hairs, kemp, etc.)

 

Published

Karoo Agric 2 (3), 26-27