Modification of cotton fiber

The method to be adopted for the elimination of salt in cotton dyeing is based on the principle of cationisation (to develop a positive charge) of cotton. The same can be achieved by subjecting the caustic-pretreated cotton fabric samples to a treatment of 1, 2-dichloroethane followed by methylamine to introduce amino groups in the cellulose structure. The treated cotton when dyed from slightly acidic bath generates positive sites due to protonation in the amino group. 

The reactive dyes being anionic (negatively charged) in solution get attracted to the positive charges on the fibre which eliminates the salt requirements for satisfactory dye exhaustion. Trials were conducted for cold brand, hot brand and highly exhaustive reactive dyes. 

The modified cotton showed excellent dye exhaustion for all the dyes in the absence of salt. The treatment was foimd to improve the dye fixation also. The modification was also assessed through elemental analysis. This study may be further extended to viscose material after suitably modifying the treatment conditions. In another trial, 3-chloro-2-hydroxypropyltrimethylammonium chloride was used as a cationic agent to cationize cotton fabric by a pad-batch process. The cationized cotton samples were dyed with different reactive dyes containing various reactive groups. The dyeability of the cationized cotton samples with reactive dyes without salt was significantly improved due to an increase in the ionic attraction between the dye and cationized cotton. The 

We all know the eonventional method of dyeing of eotton with reactive dyes alkali pH should be maintained in the dye bath. This method requires more electrolytes for exhaustion and alkali for fixation. The fibre modification technique based on polyacrylamide is when the fabric is treated with polyacrylamide the primary hydroxyl groups of cellulose is (partially) modified into a amide group, which intern leads the cellulose to act like as wool fibre and hence reactive dyes can be dyed on cotton at neutral pH in the absence of electrolyte and alkali. 

In current practice, cellulosic fibres are predominantly dyed with reactive dyes in the presence of a considerable amount of salt and fixed under alkaline conditions. However, dye fixation efficiency on cellulosic fibres is generally low (varying from 50% to 90%). This results in a highly coloured dye effluent, which is unfavorable on enviromnental grounds. Furthermore, the high concentrations (40-100 g/1) of electrolyte and alkali (5-20 g/I) are required in cellulose fiber dyeing, which may pose additional effluent problems. 

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Tsuji, W., Nakao, T., Ohigashi, K., Maegawa, K., Kobayashi, N., Shukri, S., Kasai, S., and Miyanaga, K. (1986) Chemical modification of cotton fiber by alkali-swelling and substitution reactions-acetylation, cyanoethylation, benzoylation, and oleoylation. J. Appl. Polym Sci., 32, 5175-5192. 

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