BASIC FIBRE CHARACTERISTICS

STANDARD ATMOSPHERE FOR TESTING:

A textile fiber is a peculiar object. It has not truly fixed length, width, thickness, shape and cross-section. Growth of natural fibers or production factors of manmade fibers are responsible for this situation. An individual fiber, if examined carefully, will be seen to vary in cross-sectional area along it length. This may be the result of variations in growth rate, caused by dietary, metabolic, nutrient-supply, seasonal, weather, or other factors influencing the rate of cell development in natural fibers. Surface characteristics also play some part in increasing the variability of fiber shape. The scales of wool, the twisted arrangement of cotton, the nodes appearing at intervals along the cellulose natural fibers.

Following are the basic characteristics of cotton fiber

1. fiber length
2. fineness
3. strength
4. maturity
5. Rigidity
6. fiber friction
7. structural features

STANDARD ATMOSPHERE FOR TESTING: The atmosphere in which physical tests on textile materials are performed. It has a relative humidity of 65 + 2 per cent and a temperature of 20 + 2° C. In tropical and sub-tropical countries, an alternative standard atmosphere for testing with a relative humidity of 65 + 2 per cent and a temperature of 27 + 2° C may be used.

FIBRE LENGTH: The "length" of cotton fibers is a property of commercial value as the price is generally based on this character. To some extent it is true, as other factors being equal, longer cottons give better spinning performance than shorter ones. But the length of cotton is an indefinite quantity, as the fibers, even in a small random bunch of cotton, vary enormously in length. Following are the various measures of length in use in different countries
mean length, upper quartile , effective length, Modal length,2.5% span length,
50% span length

Mean length: It is the estimated quantity which theoretically signifies the arithmetic mean of the length of all the fibers present in a small but representative sample of the cotton. This quantity can be an average according to either number or weight.
Upper quartile length: It is that value of length for which 75% of all the observed values are lower, and 25% higher.
Effective length: It is difficult to give a clear scientific definition. It may be defined as the upper quartile of a numerical length distribution eliminated by an arbitrary construction. The fibers eliminated are shorter than half the effective length.
Modal length: It is the most frequently occurring length of the fibers in the sample and it is related to mean and median for skew distributions, as exhibited by fiber length, in the following way(Mode-Mean) = 3(Median-Mean)
where, Median is the particular value of length above and below which exactly 50% of the fibers lie.
2.5% Span length: It is defined as the distance spanned by 2.5% of fibers in the specimen being tested when the fibers are parallelized and randomly distributed and where the initial starting point of the scanning in the test is considered 100%. This length is measured using "DIGITAL FIBROGRAPH"
50% Span length: It is defined as the distance spanned by 50% of fibers in the specimen being tested when the fibers are parallelized and randomly distributed and where the initial starting point of the scanning in the test is considered 100%. This length is measured using "DIGITAL FIBROGRAPH".
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