Fiber fineness

1. The influence of fineness

Fineness is normally one of the three most important fiber characteristics. A multitude of fibers in the cross- section provide not only high strength but also better distribution in the yarn. The fineness determines how many fibers are present in the cross-section of a yarn of given thickness. Additional fibers in the cross-sec- tion provide not only additional strength but also better evenness in the yarn.

About thirty fibers are needed at the minimum in the yarn cross-section, but there are usually over 100. One hundred is approximately the lower limit for almost all new spinning processes. This indicates that fineness will become still more important in the future.

Fiber fineness influences primarily: 

• spinning limit;
• yarn strength; 
• yarn evenness; 
• yarn fullness;
• drape of the fabric; 
• luster;
• handle;
• productivity of the process. 

Productivity is influenced via the end-breakage rate, the number of turns per inch required in the yarn (giving improvement of the handle), and generally better spinning conditions. In the produc- tion of blends, it must be borne in mind that, at least in conven- tional ring spinning processes, fine fibers accumulate to a greater extent in the yarn core and coarser fibers at the periphery. Blending of fine cotton fibers with coarse synthetic fibers would produce a yarn with an externally synthetic fiber character. 

2. Specification of fineness 

With the exception of wool and hair fibers, fiber fineness can- not be specified by reference to diameter as in the case of steel wire, because the section is seldom circular and is thus not easily measurable. As in the case of yarns and fibers, fineness is usually specified by the relation of mass (weight) to length: 

Tex=  of dtex=

Whereas for man-made fibers dtex is used almost exclu- sively, the Micronaire value is used worldwide for cotton. The fineness scale is as follows: 

Mic VALUE   FINENESS 

up to 3.1           very fine 

3.1-3.9              fine 

4.0-4.9              medium (premium range) 

5.0-5.9              slightly coarse 

above 6          coarse

Conversion factor: dtex = Mic x 0.394

(heavily dependent on degree of maturity). 

It should be remembered, however, that the Micronaire value does not always represent the actual fineness of the fibers. Owing to the use of the air-throughflow method for measur- ing the Mi value, for example, a low average value is obtained where there is a high proportion of immature fibers, and this does not correspond to the true value for the spinnable fibers.

Specification by linear density (tex) is more accurate in such a case, but far harder to obtain. There is a further difficulty. Cotton is a natural fiber. It grows in various soils, in various climates, and with annually changing cultivation conditions. The fibers therefore cannot be homogeneous in their charac teristics, including their fineness. Schenek [1] indicates that the Mic value varied, in an extreme example, between 2.4 and 3.9 from bale to bale in a lot of 500 bales. Long-staple cotton varieties are commonly finer than medium-staple.

3. Fiber maturity

The cotton fiber consists of cell wall and lumen. The matu- rity index is dependent upon the thickness of this cell wall. Schenek [1] suggests that a fiber is to be considered as mature when the cell wall of the moisture-swollen fiber rep- resents 50-80% of the round cross-section, as immature when it represents 30-45 %, and as dead when it repre- sents less than 25%. Since some 5% immature fibers are present even in a fully matured boll, cotton stock without immature fibers is unimaginable: the quantity is the issue. ITMF recommended the Fiber Maturity Tester FMT for cot- ton maturity determination. Measurement by FMT gives the Maturity Index (MI) refred to by Lord and Heap [3].

Immature fibers have neither adequate strength nor adequate longitudinal stiffness, they therefore lead to:

• loss of yarn strength;
• neppiness;
• a high proportion of short fibers;
• varying dyeability;
• processing difficulties, mainly at the card.

  Sources;

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