2. Importance of fibre length
• Length and fineness are related to each other in natural fibres.
(For example in cotton fibre longer the fibre finer the fibre)
• For manufactured fibres length and fineness can be controlled
separately.
• In cotton, fibre length decides the commercial value. Longer the
fibre higher the price.
• Fibre length decides spinnability that is the maximum count that
can be spun from the fibre with acceptable level of quality.
• The process parameters like drafting roller setting, yarn twist are
chosen based on the fibre length.
3. Nature of cotton fibre length
• Cotton fibre properties vary for different varieties of cotton,
for different growth areas, for different climatic conditions
and season to season.
• For cotton fibre as the length variation is higher, a large
number of fibres has to be considered to get a reliable result.
• In addition to the fibre length measurement, the fibre length
distribution is also taken into consideration.
4. Cotton fibre length measurement
Stapling Method
• This method was recommended by USDA.
• It was a system of length measurement used by classers in earlier
days to class the fibres.
• The length obtained by this method is called Staple length.
• This concept is still used by some people for the approximate
estimation of fibre length.
6. Comb Sorter Method
• This method is used to judge the fibre length distribution visually
and numerically.
• It gives a fairly accurate measurement if followed properly.
• This method uses set of top and bottom combs for the
preparation of cotton tufts of different length groups with in the
same fibre sample.
• Collection and placing of of fibre tufts of varying length
distribution on a velvet pad, which provides a diagram called
sorter diagram
• From the sorter diagram various length parameters can be
obtained
10. Optical Scanning Method
• This is the most widely used method of
cotton fibre length measurement.
• It is faster than the methods discussed
earlier and more number of samples can be
tested.
• The test results are not influenced by
personal judgement.
• This method uses a fibre sampler and a set
of combs for the measurement of fibre
length.
11. Optical scanning of test specimens
• Fibre combs are brushed carefully to remove the loose fibres
and the clamed fibres are straightened.
• The fiber combes moves into the light zone and the fibre
beard is scanned photo electrically from base to tip.
• The amount of light being used to measure the number of
fibres that extend various distance from the comb.
• From this a diagram, Fibrogram is reported.
• The fibre length is reported as span length.
13. Span length indices
• 2.5% Span length
the distance of 2.5% of the fibres extending from the clamps in which
they have been caught at random along their length. It is numerically
nearer to the staple length as determined by American classers.
• 50% Span length
the distance of 2.5% of the fibres extending from the clamps in which
they have been caught at random along their length.
• Uniformity ratio
the ratio of 50% span length to 2.5% span length and it is expressed
as a percentage.
