Technical Properties of Cotton Fiber

Properties of Cotton Fiber:
The following properties of cotton fibers are considered for cotton spinning :-

1. Fiber length : 
The average length of spinnable fibre is called staple length. Staple length is one of the most important fibre characteristics. The quality, count, strength etc. depend on the staple length of fibre.

Staple length ­ ↑.............→......... Yarn quality­ ↑

Fiber length influence :

• Spinning limit,
• Yarn strength,
• Yarn evenness,
• Handle of the product,
• Luster of the product,
• Yarn hairiness,
• Productivity.

The following length groupings are currently used in stating the trade staple: 

• Average : (25-35) mm
• Short length : 1.010" or less.
• Medium length : 1.03"  to 1.13"
• Long length : 1.16" to 1.6"
• Extra long length : 1.6" to above

2. Fiber fineness :
Fineness is one of the most important parameter determining the yarn quality characteristics. Fibre fineness influences the number of fibres in the cross section of yarn.

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 process. This indicates that fineness will become more important.

Fiber influence primarily :

• Spgn limit,
• Yarn strength,
• Yarn evenness,
• Drape of the fabric product,
• Handle,
• Luster,
• Yarn fullness,
• Productivity.

Evenness is measured in Micronaire value (MIC).

Rating of MIC value – 

• MIC value ----------------->Fineness 
• Up to 3.1 ------------very fine
• 3.1 to 3.9 ------------fine
• 4.0 to 4.9 ------------medium
• 5.0 to 5.9 ------------slightly coarse
• 5.9 to above ---------coarse.

3. Maturity : 
The maturity of cotton is defined in terms of the development of cell wall. A fully mature fiber has a well developed thick cell wall. On the other hand, an immature fibre has a very thin cell. The fibre is to be considered as mature fibre when the cell wall of the moisture-swollen fibre represents 50-80% of the round cross section, as immature when it represents 30-45% and as dead when it represents less than 25%.

Fig:Cotton fiber structure

Immature fiber leads to :

• Nepping,
• Loss of yarn strength,
• Varying dye ability,
• High proportion of short fibres,
• Processing difficulties mainly at the card

Mature fibre → Dye absorb↑ ­
Immature fibre → Dye absorb ↓.

4. Fiber Strength : 
Toughness of fibre has a direct effect on yarn & fabric strength.

Fibre strength ­ ↑→ Yarn & Fabric strength.↑ ­ ­

Very weak cottons tend to rupture during processing both in blow room & carding, creating short fibres & consequently deteriorate yarn strength & uniformity.

The following scale of value is used : 

• Below to 70% → weak,
• 70% to 74% → fairly strong,
• 75% to 80% → medium strong,
• 81% to 86% → strong,
• 87% to 92% → very strong,
• 93% & above → excellent.

5. Fiber cleanness : 
In addition to usable fibers, cotton stock contain foreign matter or trash or foreign material of various kinds :-

Vegetable matter : 

• Husk portions 
• Seed fragments 
• Stem fragments 
• Wood fragments.

Mineral material : 

• Earth
• Sand, dust, coal.

Others : 

• Metal fragments
• Cloth fragments
• Packing materials.

Foreign matter causes :

• Drafting disturbance,
• Yarn breakage,
• Filling up of card clothing,  
• Contaminated yarn.

Accepted the range of foreign matters to the Cotton Bale – 

• Up to 1.2%  → very clean
• 1.2% to 2.0% → clean
• 2.0% to 4.0% → medium
• 4.0% to 7.0% → dirty
• 7.0% & above → very dirty.

6. Colour : 
Colour is particularly important as a measure on how well a yarn or fabric will dye or bleach. Instrumental techniques for determining the colour of the sample have only now reached the Industry, HVI measurement of colour provides reasonably accurate results of average reflectance & yellowness in a sample.