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  • 2.2.7-COTTON VALUE ADDITION-COLOUR

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  • Colour

    Chapter 2 - Cotton value addition - The impact of cotton fibre properties on textile 

     
     
    Cotton is generally white when the boll opens, but continued exposure to weathering and micro-organisms can cause the cotton to lose its brightness and to become darker. Cotton may also become discoloured or spotted by the action of insects, fungi, plant diseases and soil stains, or when killed by frost or drought. Reducing sugars and storage under high humidity conditions can cause yellowing.

    Colour has little effect on processing but affects dyeing and finishing. Bleaching is often able to reduce, or even eliminate, differences present in the raw cotton. Differences in colour after bleaching do not necessarily correlate with colour differences after dyeing.

    It is important to measure not only average colour, but also colour variability, including spottedness, since this can affect processing and dyeing performance and fabric appearance. Colour is generally measured by instrument, in terms of its greyness, reflectance or brightness (Rd) and yellowness (+b), although there is a move towards CIE colour values. Trash has some affect on the measured values. Typically +b is about 9.0 and Rd 75%.