Yarns are spun from fibres by employing either the conventional ring-spinning or the new open-end spinning or the latest compact spinning technologies. The properties of cotton fibres and lint influence the yarn quality and the spinning process efficiency significantly. However, textile experts differ in their views about comparative contribution of the main fibre characteristics to yarn strength. A widely held

view is that the relative contribution of 2.5% S.L. is higher than that of fineness. The opposite view that fibre fineness contributes more than 2.5% S.L is also very strongly held. Max Preysch [1] reports following general rule for prediction of yarn strength on the basis of relative effect of fibre characteristics.

The above listed properties and fibre maturity not only contribute to the strength of yarn but also influence yarn irregularity (U%) appearance, nep content, number of imperfections and hairiness. Lint properties such as short fibre content ( S.F.C.), floating fibre index (F.F.I), trash and moisture content also influence the yarn quality, yield of yarn and process efficiency. How a spinner attempts to achieve maximum possible contribution of fibre and lint properties to yarn quality and process efficiency is briefly discussed in the following paragraphs.

1. 2.5% Span length
The spinners interpret the count and the characteristics of the yarn in terms of fibre properties of cotton most suitable for producing the required yarn. The first and foremost criterion for selection of a particular cotton is the 2.5% S.L. which indicates its spinning potential and the highest standard warp count (H.S.W.C) which can be produced from it.
In addition to the natural variations in fibre length distribution, large scale variations in all fibre properties are introduced at the growing, picking, storage and ginning stages in Pakistan because of admixture of varieties and grades! This underscore the necessity of a bale management plan so that the withdrawal of bales facilitates preparation a homogeneous mix of consistent quality on day to day basis.

Max Preysch [1] has suggested a method of calculating weighted average 2.5% S.L., S.D. and C.V% of 2.5% S.L. data pertaining to 100 bales withdrawn for preparation of daily mix. (refer to Annexure No.1). It is necessary to manage the withdrawal of bales so that C.V% of 2.5% S.L. is maintained at a minimum level.

Homogeneous mixing of consistent quality will ensure the best possible adaptation of machinery settings to 2.5% S.L. at production stages especially at the drawing frame, ensure satisfactory fibre growth, good spinning performance, process efficiency, low end-breakage rate and minimise changes of machinery settings, Spinlab [2] reports high correlation of 2.5% S.L. and yarn strength but low correlation with ends-down.

1.1 50% Span Length
Like 2.5% S.L, 50% S.L. is also an important fibre property and represents minimum distance by which at least 50% of the fibres extend into the drafting zone. Correlation between 50% S.L. and ends-down is high but low with yarn strength i.e. reverse of correlations in the case of 2.5% S.L.

1.2 Uniformity Ratio (U.R.%)
Uniformity ratio is an important fibre characteristics. It is ratio of 50% S.L. expressed as percentage of 2.5 S.L. Obviously, It indicates correlation both with ends-down and yarn strength, cotton with a U.R. of more than 50% is considered as very good and represents high correlation with ends-down evenness and yarn strength. Values of U.R.% less than 46 are considered as poor!

2. Fineness, Micronaire value (µGms/Inch)
Fineness represents weight of the fibre per unit length for which gravimetric methods are time consuming and unsuitable for routine testing in the spinning mills. Tests for fibre fineness are now-a-days performed by using modern instruments based on air flow principles such as Micronaire. These instruments measure resistance to air flow of a porous plug of a fibre sample of standard weight which is converted into fineness in micrograms per inch and is directly read from the scale of the instrument.
Number of fibres in the yarn cross-section is determined by the fineness or the micronaire value of the fibres from which the yarn has been spun. For example, cross-sections of 20 Ne yarns spun from fibre samples with fineness of 4.5 and 4.0 micrograms per inch will include approximately 166 and 190 fibres respectively. Thus, the yarn produced from the latter sample will be stronger and more even as compared to that spun from the former sample.

Fibre fineness is, therefore, a factor of greatest importance [2] in determining spinning quality i.e. H.S.W.C. yarn strength, appearance, evenness, nep content and ultimately the quality of the dyed and finished fabric. It is therefore, important to control the fineness values between bales withdrawn for the preparation of the daily cotton mixing to less than 0.2 and between mixings to 0.1.

3. Fibre maturity

Maturity of cotton fibres is defined as the degree of cell wall development in relation to the perimeter. As reported by Morton [2] wall thickness of normally ripened cotton ranges from about ¼ to 1/3 of original cell diameter. Such cottons are strongly convoluted, exhibit bean shaped cross-section fig.1 and classed as mature. Maturity of cotton fibres is highly correlated with yarn strength, low nep content, low ends down and uniform yarn appearance. Adverse climatic conditions, insects, pest attacks etc. restrict the development of the cell walls. Fibres with very little wall thickness are classed as `immature' and those with practically nil thickness as `dead' as shown in fig-2. Immature and dead fibres exhibit little or no convolutions, lack the resilience of normal fibre, form neps at the blowing and carding stages, cause high ends-down at the spindle point and create shading problems in dyed fabrics.

3.1 Measurement of maturity
Fibre maturity can be directly measured with tests of samples on the Uster AFIS®PRO, L & M modules while performing tests for fibre length. Fibre maturity can also be measured by placing a sample fibre tuft between microscopic slides, irrigating the tuft with a small quantity of 18% caustic soda and projecting the swollen fibres on the screen of a projection microscope. Mature as well as `Dead' fibres are counted. The mature fibre swell, the dead fibres do not swell. Similarly, the half mature and immature fibres can be counted. Maturity ratio

M = (normal fibres) - D (dead fibres) + 0.7
200
Maturity Ratio above 75% is considered as average and above 85% as good. Similarly maturity coefficient can be calculated as follows:

Maturity coefficient = Mature (M) + 0.6H (Half Mature) + 0.4 I (Immature)
100
Maturity coefficient = 0.85 and above is good = 0.75 is average and = 0.65 is poor.

4. Fibre Strength
As already mentioned fibre strength makes a contribution of about 20% to the strength of yarn. Maximum strength of yarn is achieved at an optimum level of twist which according to Gregory [4] represents maximum fibre cohesion as well most effective fibre strength contribution to the axial leading of the strand depending upon fibre obliquity. Because of the inclination of the fibres to the axis of the yarn component of the fibre stress resolved in axial direction balances the applied load. Thus, the fibre strength participates in load bearing partially.

Furthermore, contribution of fibre strength to the yarn strength also depends upon the types of spinning system employed and the resultant structure of yarn produced.
Helmut Deussen [5] emphasises the importance of selecting the appropriate fibre properties for the following five spinning systems in order of their importance for producing good quality yarns.
In addition to the fibre properties tabulated above, lint properties also affect the strength and quality of yarn. The influence of some of the lint properties on yarn and fabric quality and process efficiency is briefly discussed as under:

5. Immature Fibre Content (IFC)
Immature fibre content (IFC) is an important lint property. It is determined by testing cotton samples on the Uster AFIS - PRO testing instrument. The test results show the percentage of immature fibres present in the samples.

Gabriel Peters [3] investigated the impact of immature fibre content (IFC) on the dyeability and apearance of fabrics and concluded that IFC is the most decisive factor causing barriness and shading problems in dyed fabrics. According to Yankey [6] by regular monitoring of IFC, it is possible to eliminate fabric `barre' in dyed fabrics, IFC less than 8% presents no problems. Some white specks may appear if IFC is from 9% to 12%. Problems of white specks are definitely encountered if IFC is above 12%. It is, therefore, important for the spinners to include only those bales in their daily withdrawal plan with IFC less than 8% if possible. In any case bales with IFC above 12% should not be included in the mixings for regular brands of yarn and should be consumed for the manufacture of B-grade coarse category of yarns.

6. Short Fibre Content (SFC)
Short Fibre Content (SFC) reflects Floating Fibre Index (FFI) which influences quality of finished draw-frame sliver and consequently quality of the yarn produced from it.

Floating Fibre Index is a lint property derived from short fibre content (SFC) which is measured at the time of tests on fibre samples for 2.5% and 50% S.L. Correlation between F.F.I, yarn irregularity U%, I.P.I. values are high. Lower values of F.F.I. are preferred by the spinners for producing yarns according to the requirements of U% and I.P.I. specified by the end-users. Short fibre content of 10% or lower is considered as excellent which is equivalent to FFI value of about 15 or lower.
AFIS-PRO Length and Maturity Module provides accurate measurement of SFC. An increase of SFC in the card sliver indicates fibre damage and adjustment of speeds and settings of the functional parts of the Card becomes necessary. Similarly by comparing SFC of combed sliver and comber lap, comber efficiency can be improved.

7. Non-lint content (NLC) The yield of yarn from a given lot of bales is determined by the percentage of Non-Lint content which is determined by testing representative samples of the respective lots on the Shirley Analyser or the cotton analyser. Lower the % NLC, lower would be the manufacturing waste percentage and higher would be the corresponding yield of yarn. Obviously, % NLC is an important lint characteristic. According to the standard grades of the Pakistan Cotton Standards Institute (PCSI), the % NLC of the BASE Grade is 5.73%. However, as a result of poor quality ginning, the NLC%

of, commercial varieties of Pakistani cottons is generally higher than the standard percentage fixed for the BASE GRADE.

Furthermore, contaminations such as PP fibres, jute and wool fibres etc, are also generally present. PP fibre contamination is considered as the biggest hurdle in the manufacture of value-added products. Pakistani spinners are fully aware of these deficiencies of Pakistani cottons and make elaborate arrangements in their respective spinning mills for removal of contaminations and preparation of homogenous mixing for processing. The sequence, speeds and settings of machines is also adjusted to ensure maximum extraction of trash at the blowing and carding stages as a pre-requisite for producing good quality yarns.

8. Percentage moisture content or moisture regain
Cotton is a hygroscopic fibre. Its physical properties are effected by the presence of moisture in it. The wet tenacity of cotton is about 10% higher than its dry tenacity. The atmospheric conditions of temperature and R.H. in productions departments are carefully controlled to ensure correct level of moisture content in cotton with reference to the process requirements. Correlation of moisture content with the clealiness of yarn, ends down and yield is high. The standard value of moisture regain percentage of cotton under standard conditions of temperature and relative humidity is 8.5% corresponding to this value of moisture regain, the moisture content should be 7.834%. The moisture meters usually measure moisture content, the actual value of which is generally higher than the standard value in the case of Pakistani cottons. To overcome this problem, the spinners make following arrangements.

· Condition the cotton mixing prior to processing in the blow room for 24 hours at R.H. of approximately 45%, which is achieved by maintaining high room temperature of about 104ºF. After conditioning for 24 hours, the material is processed in the blow room.

· Card the material at low R.H. of about 48%.
The blowing and carding of the material under dry conditions facilitates trash extraction, R.H. in post carding stages is gradually raised to raise level of moisture content in the sliver, roving and yarn.

· The final packages of yarn are cones which are checked and passed for conditioning in the conditioning room for 24 to 36 hours in order to restore the moisture content/moisture regain to the standard level so that no loss of weight is suffered by the concerned spinning mills.
In conclusion, it must be stated that an attempt has been made in this paper to highlight the influence of fibre & lint properties of cotton on the yarn quality and process efficiency and the measures which are adopted by the spinners to produce the yarn of the quality required by the end-users.

Acknowledgement
Useful technical information received from Syed Noman Wajid, Mr. Sohail Shamim, Mr. Mahfoozul Haq Bajwa and Syed Ashraf Ali Zaidi, during the preparation of this paper is gratefully acknowledged.

References
1. Max Preysch, " New Developments of Digital - Fibrographs and their applications in cotton spinning mills", Spinlab AG, Zurich (Switzerland), October, 1973, 500 No. 216.

2. W.E. Morton, "Introduction to the study of spinning".

3. Gabriele Peters, "Significance and application of AFIS maturity measurement in cotton yarn manufacturing", Pakistan Textile Journal, June 1998.

4. Gregory, J. "Cotton yarn structure", J. Textile Institute, 41 T (1950)

5. Helmut Deussen, American Schlafhorst Company, "Conventional and Novel short-staple spinning systems", Bulletin No. 28 ( 1988)

6. Joe Yankey, "Uster® Symposium 2003: From Fibre to Fabric", Pakistan Textile Journal, February 2003.