EVALUATION OF COTTON FIBRE FINENESS:

                                                                         

The fineness of cotton fibre is a very important characteristic of fibre. It directly affects the yarn quality to be spun from a particular cotton variety. If two yarns of the same count are spun by using two cotton varieties having different fibre fineness, the remarkable difference results in the strength, evenness, and hairiness of those yarns there.

We can understand the reason behind this difference between yarn qualities to be produced.

Suppose that a yarn of 10 s count is spun with coarse fibres,  the number of fibres in the cross-section area of yarn gets lower than the required number of fibres. Thus the low yarn strength results in the yarn.  If the number of fibres of the cross-section area of the yarn gets increased more than required,  these fine fibres result in the form of improved yarn strength.

The coarse fibres also result in the form of unevenness. How does it happen? The cotton fibres differ in fineness from one to another within the variety. Here more fibres of finer fibres always have greater chances to result in the form of improved evenness than the yarn spun with the lower number of fibres of coarse fibres.

The fineness of fibre tells us about the diameter of fibre or dimensions of the cross-section of the fibre. Since cotton fibres do not have a regular diameter or cross-sectional dimension so that it gets almost impossible to determine the cross-sectional dimensions or diameter accurately. The linear density of fibre is measured. “Weight per unit length of fibre or linear density of fibre is called fibre fineness”. The unit of fibre fineness micrograms/inch is commonly used.

A micronaire instrument working based on airflow is commonly used to examine the fineness of cotton fibre. “This instrument works on the resistance offered to the flow of air through a plug of fibres. It means how much air gets passed through the plug of cotton fibres to be tested. The resistance to airflow depends upon the specific surface area of fibres”. The maturity ratio of fibres also affects the specific surface area. If the maturity ratio of the cotton fibres sample varies highly the readings of the micronaire meter are treated with a high degree of cautions. In the micronaire meter, an amount of 3.24 grams of cotton from the sample is taken. Now this weighed amount of cotton is well opened. This well-opened cotton is compressed into a cylindrical container of fixed dimensions. The compressed air is passed through the sample at a definite pressure and the volume rate of the flow of air is measured by a rotometer type air flowmeter. The sample for the micronaire test should be well opened cleaned, and thoroughly mixed ( by hand fluffing and opening method).  The low meter reading indicates that fibre is fine. The grading is done as below:

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