The influences of cotton fibre characteristics in yarn manufacturing

INTRODUCTION

The quality of the yarn depends on the fibres. Therefore, it is important to keep mind to the characteristics of the fibre and the production cost before manufacturing the yarn. Because yarn production costs 50-65% of the purchase price of fibre. Therefore, it is an important challenge to produce good quality yarn and reduce production costs at the same  time. That is why it is important to know the quality of fibre and influences.

The influences of fibre properties in yarn production is discussed below:-

1. The influences of fibre fineness

Fibre fineness is one of the three important properties of fibre .The finer the fibre ,the more number of fibres in the cross section of the yarn. The cross section of the yarn should have a minimum of 30 fibres though generally above 100.The number of fibres in the cross section of the yarn not only increases the strength of the yarn but also helps in increasing the uniformity of the yarn. In addition, the higher the fineness of the fibre, the higher the count of yarn. Thus the spinning limit depends on the fineness of the fibre. The higher the fineness of the fibre, the higher the strength of the yarn. 

Fiber fineness is usually expressed in micronaire value. Incase of cotton fibres, the fineness of the fibre is expressed in micronaire value and incase of synthetic fibres, the fineness is expressed in detex and denier. 1 inch fibre weight expressed in micrograms.

Conversion factor dtex =Mi X 0.394

It should be remembered, that the micronaire value does not always reflect the actual fineness of the fibre.It depends on the method of air flow and the sample fibre.

Fibre fineness also affects yarn fullness, drape of the fabric, lusture, handle, productivity of the peocess.

The fineness scale is as follows:-

Micronaire value                                       Fineness

       up to 3.1                                              very fine

       3.1-3.9                                                 fine
       4.0-4.9                                                 medium   
       5.0-5.9                                                 slightly coarse
       above 6                                                coarse

2. The influences of fibre maturity

The maturity of the cotton fibre depends on the cell wall. The cell wall of mature fibres is thick, while that of immature fibres is thin. Immature fibres create neps and absorb more dystuff at dyeing resulting in shade variation.

Under the microscope we can see three types of cotton fibres.

1. Normal fibres look like rods, continuous lumens are not seen.

2. A continuous lumen is seen in the dead fibre and looks like a ribbon.

3. The scales of thin wall are ripened ball.

Immature fibre are affects 

• Longitudinal stiffness.
• Decreased yarn strength.
• Short length fibers are more.
• Carding is difficult to process.
• Increases neps.

3. The influence of the fibre length 

The length of the fiber is very important especially in the case of ring spinning. The setting of the machine in each section depends on the length.Also affects production, end brakage, waste, twist, depending on length and length distribution. Fibres below 4-5 mm in length create waste and fly. Fibre of 12-15 mm length does not affect the strength of the yarn, but fullfill the yarn and produces positive multiplication in the fibre of the above length.

Fibre length usually affects

• Spinning limit
• Productivity
• Yarn strength
• Yarn evenness
• Hairiness
• Handle of the product
• Lusture of the product

Classification of fibre according to span length:

Fibre Type	2.5% span length(mm)
Extra long staple	33.0 mm & above
Long staple	29.5 mm to 32.5 mm
Medium staple	25.0 mm to 29.0 mm
Short staple (A-type)	20.5 mm to 24.5 mm
Short staple ( B-type)	20.0 mm & above

4. The influences of fibre strength

The strength and elongation of the fibre is determined by the toughness of  fibre which directly effects strength of the yarn and fabric.Very weak fibres rupture into blow-room and carding and creating short fibres, resulting in deterioration of yarn strength and evenness. Fibre strength is usually tested in bundle form because it represents the binding strength similar of the yarn rather than the single fibre.The minimum strength of textile fibre is approximately 6 cN/tex. A maximum of 30-70% of the fibre strength can be utilized through spinning of the fibre. The breaking strength of some fibres is given :

            Polyester fibre :    35-60 cN/tex

            Cotton              :   15-40 cN/tex

            Wool                :    12-18 cN/tex

Fiber bundle strength is measured and stated as pressley value

in the case of cotton. The following scale value  is used:

            

            93 and above = excellent

            87-92             = very strong

            81-86             = strong

            75-80             = medium

            70-74             = fair

            under 70        = weak

The physical unit should not be converted because the measurement method is not very exact. The moisture content of the fibre depends on the ambient-air, so it is important to know that fibre testing other than synthetic, depending on the climatic conditions and the time of exposure.

5. The influences of fibre elongation

Breaking strength and elongation are two prime quality attributes of any spun yarn. The strength and elongation of a yarn are important to the process ability of the yarn in the downstream processing and operational life of the substrate made with the yarn. Elongation is determined as a  percentage of starting length. Products without elasticity will hardly be usable. The product must be deformed (e.g. at knee, elbow) under high pressure and during processing but it will return if there is elongation capacity

For example , form the difference in their elongation: 

Cotton= 6-10% , wool=25-45% In generally, higher elongation of textile products are neither necessary nor desirable, but processing at spinning is difficult, especially in the drawing process. Exceptions are stretch products, sports wear etc. 

If a fibre is applied to a tensile loading, then strength and elongation are both demands. Strength and elongation are inseparably related, the relationship is expressed in the stress/strain diagrams.

6.The influences of fibre stiffness

The stiffness of the fibre is very important when rolling, twisting and revolving are required. If the stiffness of the fiber is too high, it is difficult to adapt to revolving, producing hairiness and not being able to return to shape after deformation of the product. In most cases neps makes .They do not have longitudinal resistance, the stiffness of the fibres is related to fibre substance, length and fineness of the fibres. Fibres of the same substance have higher stiffness of short length fibres. Since the fibres are bound to air during the formation of yarn in the ring spinning machine, the slenderness ratio(stiffness) determines somewhat where the fibre finish up, the fine fibre or long fibre in the core, and the coarse or small fiber in yarn surface.

$$Eatbreak=100(ΔLbreak/Lo)