To evaluate the quality of raw materials (Fibers) two important properties need to be considered namely fiber length and fiber fineness. Fiber length is mainly considered for natural fibers as both length and fineness can be controlled in case of man-made fibers. Especially in case of cotton fiber cotton fiber length is important as length may differ from fiber to fiber.
One of the properties of cotton which is to be measured is staple length. Staple length is defined as the quantity estimated by personal judgement by which a sample of fibrous raw material is characterized as regards its technically most important fiber length.
Importance of fiber length:
Fiber length helps for Quality assessment, fiber breakage study, machine study, combing efficiency, etc.
Long fibers can be processed easily. More even yarns can be produced from long fibers because there are less fiber ends in given length of yarn. High strength yarn can be produced from long staple fibers at same level of twist.
The length and fineness are sometimes related in natural fibers whereas for man-made fibers, length and fineness can be controlled separately.
Fiber Length Parameters:
Mean length: It is defined as the average length of all fibers in the sample, based on weight – length or relative number – length distribution.
Upper Quartile length: It is defined as the length which is exceeded by 25% of the fibers, by weight or number in the sample.
Effective Length: It is the Upper quartile length of the distribution excluding fibers below half the upper quartile. It is obtained by the geometrical construction on a cumulative length frequency diagram based on number.
Modal Length: It is the most Frequently occurring length of fibers in the weight distribution of the sample, i.e., it is the length of the group of fibers where a greater number of fibers will be having equal length.
Percentage Short Fibers: This is percentage of fibers, the length of which are equal to or less than half the effective length.
Dispersion: It represents the variation in the length of fibers. It is the interquartile range expressed as a percentage of effective length.
Span Length: It is a distance from a line where the fibers are randomly caught to a point where only a certain percentage of fibers extend 2.5% span length is the distance from the clamp on a fiber beard to a point up to which only 2.5% of the fibers extend. 50% span length is the distance of the point to which 50% of the fibers extend and 66.7% span length is the distance up to which 66.7% of the fibers extend.
Uniformity ratio: It is the ratio between 50% span length and 2.5% span length expressed as a percentage.
Determination of fiber length:
Methods of measuring the fiber length
The technician and the graders method.
The technologist method.
The technologist method is further classified as following:
Direct method – (a) single fiber, (b) Groups of fibers.
Eg. Baer Sorter, Shirley Comb Sorter.
Semi direct method – Eg. Ball sledge sorter.
Indirect method – Eg. Fibrograph, Uster Stapler.