Influential Properties of Cotton Fiber in Spinning

Cotton is a natural cellulosic fiber that produces a variety of yarn due to its diversified end-use. On the basis of different end-use, cotton fiber is selected for spinning keeping in mind its different quality parameters. To produce a standard quality cotton yarn the fiber should have the following properties in an optimum level. The most important characteristics considered for the fiber are:

  1. Fiber fineness
  2. Staple length
  3. Fiber strength
  4. Length uniformity
  5. Fiber maturity
  6. Color grade
  7. Fiber cleanness
  8. Elongation
  9. Moisture

1. Fiber Fineness

Fiber fineness is the supreme consideration that governs the yarn eminence. Fineness limits the numerical amount of fibers that exist in the cross-section of yarn. Supplementary fiber in the cross-section offers not only superfluous strength but also an enhanced fiber distribution in the yarn. At least thirty fibers are necessary in the yarn cross-section, but there are typically over 100 for almost every spinning system available.

Grades Based on Fiber Fineness

Fiber Fineness (Fiber Diameter)

Fiber Fineness Influences

If fineness increases then,

  • Spinning limit increases
  • Yarn strength increases
  • Yarn evenness increases
  • Drape of the fabric increases
  • Lusture increases
  • Handle increases
  • Productivity increases

What is MIC Value?

For cotton, fiber fineness is quantified by MIC value or Micronaire value (microgram/inch). It indicates the average mass of per inch the fiber in microgram. As the value of MIC gets higher the fiber gets finer. This is more like a direct count measuring method. The fineness scale is as follows:

Micronaire (MIC) Fineness
Bellow 3.0 Very Fine
3.1-3.9 Fine
4.0-4.9 Medium
5.0-5.9 Coarse
Above 6.0 Very Coarse

2. Staple Length

One of the utmost significant characteristics of cotton is fiber length. It defines the maximum spinning limit of the fiber. The run-of-the-mill length or the mean length of fiber ready for spinning is said to be the staple length. Staple length determines the ultimate quality, maximum count and tenacity of yarn.

 If fiber length rise then,

  •  Spinning limit increases
  •  Yarn strength increases
  • Yarn evenness increases
  •  Hand feel of the end product increases
  • Lusture  increases
  • Yarn hairiness decreases
  • Productivity increases

Fiber Type

Length in Inch

Length in mm

Short Staple – SS

1 inch or below

25mm or below

Medium Staple – MS

1 1/32-1 4/32 inch

26mm – 28mm

Long Staple – LS

1 5/32-1 12/32 inch

29mm – 35mm

Extra-long Staple – ELS 1 13/32 inch & above

36mm & above

3. Fiber Strength

  • Robustness of fiber has an undeviating consequence on yarn and its fabric tensile strength.
  • When the fiber strength improved then yarn and fabric strength amplified.
  • Very fragile cottons tend to falling-out throughout processing both in blow room (while expose to beater) and carding generating short fibers and consequently decrease yarn strength and consistency.
  • Bottom strength for textile fabric is approximately 6 cN/Tex (about 6 Km breaking strength)
  • A few examples of breaking strength: (in cN/Tex)

Cotton                   16 – 41

Wool                     13– 19

Polyester               32 – 59

  • In relation to cotton, the strength of fiber bundle is dignified and stated as the Pressley Index (PI) and PSI (Pounds per Square Inch).

Pressley index (PI) = Breaking load (lbs) ÷ Bundle weight (mg)

The following scale of PI value is used:

PI Value

Grade

Below 70

Weak

70 – 74

Fairly Strong

75 – 80

Medium Strong

81 – 86

Strong

87 – 92

Very Strong

93 And Above

Excellent

4. Length Uniformity

If length uniformity increases then,

  • Yarn irregularity decreases
  • Ends down decreases
  • High wastage in combing decreases
  • High fly liberation and machine contamination in spinning, weaving and knitting decreases

There are two popular measures of length uniformity in a cotton sample:

  1. Uniformity Ratio (UR) and
  2. Uniformity Index (UI)

These two can be denoted as following

Uniformity Ratio, UR = (50% Span Length ÷ 2.5% Span Length) x 100

UR range is 75% -85%

Uniformity Index, UI = (Mean Length ÷ Upper Half Mean Length) x 100

UI range is 40% -50%

5. Fiber Maturity

The maturity of cotton is distinct in terms of the progress of cell wall thickness. An entirely matured fiber has a well-developed thick cell wall. On the other hand, an immature fiber has comparatively thin cell wall. If the moisture swollen fiber’s cell wall represents 50% – 80% of its round cross section then the fiber is to be denoted as mature fiber. The fiber is to be considered as immature when it epitomizes 30% – 45% and as dead when it symbolizes not as much of its 25%.

Cotton Morphology

Physical Structure of Cotton Fiber

Fiber Maturity

Cross-section of Cotton Fiber


Immature fibers lead to

  • Deterioration of yarn strength
  • Neppiness (neps)
  • Erratic dye ability
  • Greater share of short fibers
  • Handling difficulties mostly arise at the carding
  • Low dye adsorption whereas mature fiber shows higher adsorption of dye

Maturity is expressed as Maturity Ratio.

Maturity Ratio = {(N-D) ÷ 200} + 0.7

Where, N = Normal (mature) fiber and D = Dead fiber.

This equation is known as Lord’s equation.

The grading of maturity ratio is:

Maturity Ratio Grade
0.86 Good
0.75 Average
.65 Poor

6. Color Grade

Color grade denotes the amount of the reflectance (Rd) and the yellowness (+b) of cotton fibers. Reflectance (Rd) refers to the whiteness of the light that is imitated by the cotton fibers and (+b) states the yellowness of the light that is replicated by the cotton fibers.

Classer’s Designation for Reflectance

Classer’s Designation for Yellowness

White

Light Spotted

Spotted

Tinged Yellow Stained

Good Middling

11*

12

13

Strict Middling

21*

22

23*

24

25

Middling

31*

32

33*

34*

35

Strict Low Middling

41*

42

43*

44*

Low Middling

51*

52

53*

54*

Strict Good Ordinary

61*

62

63*

Good Ordinary

71*

Below Grade

81*

82

83

84

85

[ * stands for quantitative standards, while the others are qualitative standards ]

7. Fiber Cleanness

A bale of cotton contains not only the fresh cotton fibers but also provides a certain amount of impurities. In addition to operating fibers, cotton stock encloses foreign matter of numerous kinds. A list of impurities is provided here that is mostly found in cotton bale (Not in the garden-fresh fiber).

Vegetable Matter

  • Husk portions
  • Seed wreckage
  • Steam remains
  • Leaf fragments
  • Wood trashes

Mineral Matter

  • Earth
  • Sand
  • Dust
  • Coal

Other Foreign Matter

  • Metallic
  • Dry goods fragments
  • Storing material
  • Cloth particles
  • Packing elements

8. Elongation

Elongation is a quantity of the elastic performance of the fibers in the bundle. The stretched length of fibers right before they breakdown is said to be as its elongation percentage.

Elongation % Grade
Less than 5% Very low
5% – 5.8% Low
5.9% – 6.7% Medium
6.8% – 7.6% High
Above 7.6% Very high.

9. Moisture

Moisture is the proportion of water that is existent in the sample. It fluctuates in the cotton with relative humidity, time, temperature and previous history of the fiber. The moisture content of cotton fiber is 7.5% and moisture regain is 8.5%.

Moisture content Grade
Below 4.5 Very low
4.5-6.5 Low
6.5-8.0 Medium
8.0-10.0 High
10.0 and above Very high

 

Frequently Asked Questions

1. Fiber contains numerous qualities. Which one of them should be prioritized?

Fiber possess a lot of properties. The end use of the product determines its selection for spinning. For cotton fiber fineness and length is the most significant criteria. Besides, moisture, trash content and elongation comes as well.

2. What is the differences between moisture content and moisture regain?

The moisture content stands for the quantity of water exist in the fiber as a percentage of sum of weight of the fiber. Whereas, moisture regain denotes the extent of water exist in the fiber as a proportion of its oven dry weight. That is why the value of moisture regain is always higher than the moisture content.

For cotton, moisture regain is 8.5 whereas moisture content is 7.5

3. What is the difference between short fiber and short staple fiber?

Normally a fiber is to be counted as short fiber if its length is below 12.5 mm. The fibers which are removed in combing are also known as short fiber or noil. But, short staple fibers are those whose length is 12.5 mm to 25 mm.

 

References:

  1. W. Klein (2014). The Rieter Manual of Spinning – Volume 1: Technology of Short-Staple Spinning
  2. C.Yu (2014). Natural Textile Fibres: Vegetable Fibres
  3. Automatic Bale Opener UNIfloc A12
  4. Short Staple Fibers
  5. Bale Manager Module
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