Test Methods and Precautions

Cotton Fibre

  • Maturity Coefficient
  • Caustic soda method - Fibres irrigated in 18% caustic soda are examined under microscope. Based on the ratio of lumen width to wall thickness, fibres are classified as Mature, Half Mature and Immature
    Mature (M) - L/W <1
    Half Mature (HM) - 1 < L/W < 2
    Immature (I) - L/W > 2
    Mc = (M + .6*H + .4 * I)/100
    American Method
    Mature (N) - L/W < 2
    Immature (D) - L/W >or= 2
    Maturity Ratio Mr = (N -D)/200 + 0.7
  • Polarised Microscope Method
    Immature - Blue or purple
    Mature - Yellow or Green
  • Differntial Dyeing
    Fibres dyed in boiling dyebath containing .036g Diphenyl Fast Red 5BL and .084g Chloarantine Fast green in 120g of water
    Mature - dyed to red
    Immature Dyed to Green
  • Bundle Strength
    • Pressley - Operates on constant rate of traverse. Rate of loading increases with traverse and there is risk of overshootin and overestimation of strength
      Pressley Index(PI) = Breaking strength at "0" gauge length in pounds/weight in mg
      Pressley Ratio(PR) = Breaking strength at 3mm gauge length in lbs/weight in mgs
      Tenacity at"0" gauge length, g/tex = 5.36 * PI
      Tenacity at 3mm gauge length,g/tex = 6.8 * PR
      Tensile strength in 1000psi = 10.81 * PI
      Breaking tenacity, g/tex = Breaking strength in 1000psi *0.496
    • Stelometer- operates on constant rate of loading. Generally preferred
  • Trash content
    Shirley Analyser is the standard equipment used for measrement of trash content. The equipment determines
    • primary tash consisting of coarse type of trash including seed coats
    • Finer trash
    • Micro dust larger than 150 microns
    • Microdust between 50 and 150 microns. About 200 gms of cotton are used and the test takes about 1hr
  • Denkendorf Mirodust and Trash Analyser
    enables quick estimation of trash from 25- 30 gms in 12-15min
  • Nep Content
    Neps represent small pin size entanglements of fibres which detract from appearance of yarn and fabric. They take up less dye and show up as specks in dyed fabric. In most cases neps are formed by immature fibres because of their low rigidity. Sometimes neps are also formed because of seed coat fragments which provide nucleus for them.
    • Manual method - Small pinches of opened fibres are laid on a black plush board of known area and neps are counted manually. This is subjective and time consuming.
    • Nepotometer - This is a miniature card where fibres are opened into a web and the web is compared against standard boards.
    • Shirley Web template - Card web is collected on a black board on which a template containing 34 circular holes of one square inch each is laid. Number of holes containing at least one nep is counted. Assuming a Poisson distribution for nep incidence, Nep level is estimated.
    • Uster AFIS -Opened fibres pass through a sensor. A computer is used to distinguish individual fibres from neps.
  • HVI Testing
    Conventional testing involves considerable time and results are not available in time for cotton selection and mixing preparation. High volume Instument(HVI) have speeded up testing substantially and testing of a cotton is completed in about 2-4 minutes. Bale wise testing of cootons is possible and bales with substandard characteristics can be weeded out.HVI determines Upper half mean length or 2.5 and 50% span lengths, uniformity index or ratio, Micronaire and bundle strength. Optional attachments for estimating trash level by optical scanning and colour of cotton and moisture level are available. In Micronaire test HVI requires an approximate weighment of cotton. As an option Macromat which measures both fineness and maturity can be incorporated in HVI. HVI, though rapid, has certain limitations in terms of accuracy of results. These include in case of
    • Fibre Length
      Fibre breakages occur during comb preparation on HVI as this is done at high speed. Such breakages are more with harsh, entangled cottons. This results in lower estimates of fibre length. Breakages are also higher with card sliver compared to comber sliver.Over estimation of fibre fractionation is therefore found in HVI.
    • Bundle Strength
      • HVI works on constant rate of extension while stelometer works on constant rate of loading. Further, time for break is much lower in HVI to speed up testing.
      • A randomly clamped beard is used is used in stelometer and fibres are combed to remove short fibres. So all fibres are gripped by both jaws. In HVI, fibre bundle is not combed to remove short fibres before clamping. All fibres are therefore not clamped by both jaws.
      • The mass of broken specimen is weighed in a balance in stelometer while in HVI indirect estimate of mass (by optical means) is obtained. The state of crimp in the fibre affects the estimated mass.

      As a result, significant differences are found in bundle strength values by HVI and conventional testing. HVI does not give true results for material at different stages of spinning.
    • Uster-AFIS
      Fibre samles are opened into individual fibres by an opening roller and passed on to different modules for measuring
      • fibre Length
      • Fibre Fineness
      • Maturity
      • Nep content

      Nep measurement is the most useful part of this instument. A computer distinguishes individual fibres from neps. Seed coat neps are separately assessed. A good correlation is claimed between neps measured with AFIS and neps in yarn by Uster imperfection tester. A second sensor measures trash and dust.
  • Man made fibre Filament and Yarn