Dyeing behaviour of lyocell fabric: effect of NaOH pre-treatment |
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Authors: | Parikshit Goswami Richard S Blackburn Jim Taylor Patrick White |
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Institution: | (1) Green Chemistry Group, Centre for Technical Textiles, University of Leeds, Leeds, LS2 9JT, UK;(2) Lenzing Fibers, Lenzing, Austria |
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Abstract: | To understand the effect of alkali pre-treatment on the dyeing of lyocell fabrics, samples are pre-treated with 0.0–7.0 mol dm−3 NaOH using a pad-batch process and then dyed with different types of reactive dyes. Exhaustion, fixation, and visual colour
strength (K/S values) are measured. It is observed that sodium hydroxide pre-treatment significantly improves the colour yield, exhaustion,
and fixation for all dyes used. Highest K/S values are obtained when the fabrics are pre-treated with 2.0–2.5 mol dm−3 NaOH. Cross-sectional analysis shows that below this optimum concentration the core fibres in the yarn are not dyed; at optimum
concentration all fibres in yarn cross-section are homogeneously dyed. Cross-sectional analysis shows that as the pre-treatment
concentration of NaOH increases above 2.5 mol dm−3, the fibres change progressively from a circular to angular cross-section, forming a solid unit. The decrease in K/S above the treatment concentration of 2.5 mol dm−3, though the %E and %F remains almost constant, is attributed to the distribution of dye over a larger surface area of the outer fibres in the yarn
cross section, forcing the K/S at λmax to decrease.
This paper was presented at the 2nd International Cellulose Conference, Tokyo, Japan, 24th October 2007. |
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Keywords: | Regenerated cellulose Cellulose II Sodium hydroxide Swelling Reactive dyes Diffusion Morphology |
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