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FIBRE TESTING - 2

fibre testing

A large proportion of short fibre leads to strong fly contamination, strain on personnel, on the machines, on the work room and on the air-conditioning, and also to extreme drafting difficulties.

A uniform yarn would have the same no of fibres in the cross-section, at all points along it. If the fibres themeselves have variations within themselves, then the yarn will be more irregular.

If 2.5% span length of the fibre increases, the yarn strength also icreases due to the fact that
there is a greater contribution by the fibre strength for the yarn strength in the case of longer fibres.

Neps are small entanglements or knots of fibres. There are two types of neps. They are 1.fibre neps and 2.seed-coat neps.In general fibre neps predominate, the core of the nep consists of unripe and dead fibres. Thus it is clear that there is a relationship between neppiness and maturity index. Neppiness is also dependent on the fibre fineness, because fine fibres have less longitudinal stiffness than coarser fibres.

Nature produces countless fibres, most of which are not usable for textiles because of inadequate strength.

The minimum strength for a textile fibre is approximately 6gms/tex ( about 6 kn breaking length).

Since blending of the fibres into the yarn is achieved mainly by twisting, and can exploit 30 to 70% of the strength of the material, a lower limit of about 3 gms/tex is finally obtained for the yarn strength, which varies linearly with the fibre strength.

Low micronaire value of cotton results in higher yarn tenacity.In coarser counts the influence of micronaire to increase yarn tenacity is not as significant as fine count.

Fibre strength is moisture dependent. i.e. It depends strongly upon the climatic conditions and upon the time of exposure. Strength of cotton,linen etc. increases with increasing moisture content.

The most important property inflencing yarn elongation is fibre elongation.Fibre strength ranks seconds in importance as a contributor to yarn elongation. Fibre fineness influences yarn elongation only after fibre elongation and strength. Other characters such as span length, uniformity ratio, maturity etc, do not contribute significantly to the yarn elongation.Yarn elongation increases with increasing twist. Coarser yarn has higher elongation than finer yarn. Yarn elongation decreases with increasing spinning tension. Yarn elongation is also influenced
by traveller weight and high variation in twist insertion.

For ring yarns the number of thin places increases, as the trash content and uniformity ratio increased For rotor yarns 50%span length and bundle strength has an influence on thin places.

Thick places in ringyarn is mainly affected by 50%span length, trash content and shor fibre content.

The following expression helps to obtain the yarn CSP achievable at optimum twist multiplier with the available fibre properties.


Lea CSP for Karded count = 280 x SQRT(FQI) + 700 - 13C

Lea CSP for combed count = (280 x SQRT(FQI) + 700 - 13C)x(1+W)/100

where,
FQI = LSM/F
L = 50% span length(mm)
S = bundle strength (g/tex)
M = Maturity ratio measured by shirly FMT
F = Fibre fineness (micrograms/inch)
C = yarn count
W = comber waste%

Higher FQI values are associated with higher yarn strength in the case of carded counts but in combed count such a relationship is not noticed due to the effect of combing

Higher 2.5 % span length, uniformity ratio, maturity ratio and lower trash content results in lower imperfection. FQI does not show any significant influence on the imperfection.

The unevenness of carded hosiery yarn does not show any significant relationships with any of the fibre properties except the micronaire value. As the micronaire value increases, U% also increases. Increase in FQI however shows a reduction in U%.

Honey-dew is the best known sticky substance on cotton fibres. This is a secretion of the cotton louse. There are other types of sticky substances also. They are given below.

  • honey dew - secretions
  • fungus and bacteria - decomposition products
  • vegetable substances - sugars from plant juices, leaf nectar, overprodcution of wax,
  • fats, oils - seed oil from ginning
  • pathogens
  • synthetic substances - defoliants, insecticides, fertilizers, oil from harvesting machines

In the great majority of cases, the substance is one of a group of sugars of the most variable composition, primarily but not exclusively, fructose, glucose, saccharose, melezitose, as found, for example on sudan cotton. These saccharides are mostly, but not always, prodced by insects or the plants themselves, depending upon the influence on the plants prior to plucking. Whether or not a fibre will stick depends, not only on the quantity of the sticky coating and it composition, but also on the degree of saturation as a solution. Sugars are broken down by fermentation and by microorganisms during storage of the cotton. This occurs more quickly the higher the moisture content. During spinning of sticky cotton, the R.H.% of the air in the production are should be held as low as possible.

The following table  shows the degree of correlation between the various cotton fibre quality characteristics and those of the yarns into which these fibres are spun  -  RING SPUN YARNS

yarn evenness imperfection and classimat faults breaking tenacity breaking elongation hairiness
fibre length
micronaire value
nep, trash, leaf, microdust, fibre  fragments
1/8" breaking strength
1/8" elongation
colot/reflectance

                      

significant correlation

      

good correlation

 

little or no correlation

 

 The following table shows the degree of correlation between the various cotton fibre quality characteristics and those of the yarns into which these fibres are spun - ROTOR SPUUN YARNS.

  yarn evenness imperfections and classimat faults breaking tenacity breaking elongation hairiness
fibre length          
micronaire value          
nep, leaf, trash,microdust, fibre fragments          
1/8" breaking strength          
1/8" breaking elongation          
color/ reflectance          

significant correlation

      

good correlation

 

little or no correlation

 

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