Constrained by lack of availability of suitable land the consumption of cotton has leveled off while that of polyester has increased rapidly, the demand for clothes, which are made from cotton is increasing in the highly sophisticated countries. Cotton production is criticised as it is a polluting process and the land could be used for food production in the poor countries. Therefore much attention has been directed towards re-engineering of synthetic fibres aimed at mimicking cotton properties such as breathability, comfort, antistatic and dyeability. Even so world cotton production is still growing slowly; it is expected to increase to 20.1 m tonnes for 2003/04, according to the International Cotton Advisory Committee. It is likely that there will always be a demand for cotton, and more research will be directed to environmentally friendly cotton production, coloration and finishing. Coloration of cotton is carried out by using vat, sulphur, azoic, direct and reactive dyes. Reactive dyes are a very important group of dyestuffs for colouring cotton because of their desirable properties which include unrestricted shade range, ease of application, low cost and good fastness to light, washing and rubbing. When they are applied to cellulose by an exhaustion process, they require relatively high levels of electrolyte (salt) to increase the substantivity of the anionic dyestuff for cellulose and thereby achieve high visual colour yields. Discharge of highly saline effluent is becoming environmentally less acceptable, as increased salinity in rivers upsets the delicate balance of aquatic flora and fauna. Hence some recent developments in cotton dyeing with reactive dyes have focused on reduced salt usage. This thesis evaluates one of the options for low salt cotton reactive dyeing; chemical modification (pre-treatment) of cellulose with cationic agents. This has the effect of eliminating the inherent electrostatic repulsion between the anionic (negative) dye and the fibre, so that the use of electrolyte can either be reduced or eliminated. The (negative) surface charge of cotton was modified to a positive charge by using initially a commercial polymeric cationic fixing agent. The amount of cationic agent applied by an exhaustion technique to a cotton fabric, was quantitatively determined using Congo Red, the method being based on the titration of a known concentration of Congo Red with a solution of the treatment agent. The application of this procedure to determine the exhaustion properties of potential cationic pre-treatment agents for cotton was then studied. The pre-treated cotton was dyed to evaluate the effect of the treatment on both dye exhaustion and fixation under three different sets of dyeing conditions and a comparison was made with untreated cotton dyed conventionally. Lower colour yield, inferior wash and light fastness, shade change, ring dyeing and poor migration (levelness) were obtained on the pre-treated fabric. Therefore, pre-treatment of cotton with polymeric cationic agents was adjudged to be of no further interest. To avoid the technical problems associated with the use of polymeric pre-treatment agents, further modification of cotton was carried out with low molecular weight (monomeric) species. A systematic study of the introduction of different amino groups into cotton, via reaction with a commercially available reactive, water soluble dichlorotriazine agent followed by amination with different amines, was undertaken. Where possible, the characterization of the reaction products was made by using a variety of analytical methods. Once the resulting adducts had been characterised, the dyeing behaviour of reactive dyes on the derived substrate was evaluated. The present study also involved the synthesis and application of other pre-treatment agents, e.g. 2,4-bis(4-sulphophenylamino-)-6-chlorotriazine and dyes with a view to obtaining a better understanding of the causes of the shade changes arising from the use of cationic agents to cotton.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:488431 |
| Date | January 2004 |
| Creators | Erdas, Yonca |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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