The Reactive Dyeing of Cellulosic Fibres

The present study is mainly directed at achieving high fixation efficiency of reactive dyes on cotton in order to solve the remaining problems with the use of this type of dyes, e.g. the necessity of using expensive and time-consuming wash off procedure and of using high concentration of electrolyte to exhaust the dyebath. A number of ways to modify cotton have been sought to achieve the above objectives. Modification of cotton with a polyamide epichlorohydrin (PAE) resin and its derivatives was extensively studied; three simple pretreatment methods have been proposed and mechanistic implications are also discussed. Light fastness of the dyeings produced on cotton modified with polymeric compounds was compared to that achieved on cotton modified with low molecular weight compounds. It is concluded that reduction of light fastness of reactive dyeings always occurs on the former polymer modified substrate whilst there is no such problem with the dyeings on the latter substrate. Modification of cotton with a specially synthesized low molecular weight compound, 1,1-dimethyl-3-hydroxyl-1-azetidinium chloride (DMAC), and a commercially available compound, Glytac A, were carried out and the dyeability of the subsequent substrate was studied. The practical importance of these methods and the mechanism of covalent bond formation when using reactive dyes on these substrate are discussed. A systematic study of introducing different amino groups into cotton via reaction of cotton with N-methylol acrylamide followed by amination with different amines was undertaken and the dyeing behaviour of reactive dyes on the substrate produced was evaluated. An unusual reaction was observed when further treating cotton which had been pre-esterified with chloropropionyl chloride (CPC) in an aqueous solution of amines. Amination under severe conditions led to substrates which are dyeable with reactive dyes with good fastness properties but amination under much milder conditions produced substrates which gave the subsequent dyeings of poor wash fastness. A method to determine the chlorine content in CPC cotton by ion-exchange chromatography is discussed. An alternative way to achieve dye-fibre covalent bonding was proposed: cotton was activated first and then dyed with alkyl-amino dyes. The ways of cotton activation, the methods to prepare alkyl-amino dyes and activation agents are discussed. This approach not only imparts high efficiency to the fibre-dye reaction but also avoids the problem of dye hydrolysis. The present study has thus far produced six papers which have been published during the course of this project. The Journal names and the other details about the publications were given as follows: [1] S.M. Burkinshaw, X.P. Lei and D.M. Lewis, J.S.D.C., 105(1989) 391-398. [2] D.M. Lewis and X.P. Lei, Text. Chem. and Col., 2J_(1989) 23-29. [3] S.M. Burkinshaw, X.P. Lei, D.M. Lewis, J.R. Easten, B. Parton and D.A.S. Phillips, J.S.D.C., J_06(1990) 307-315. [4] X.P. Lei and D.M. Lewis, J.S.D.C., 106(1990)352-356. [5] D.M. Lewis and X.P. Lei, J.S.D.C., 107(1991 )102-109. [6] X.P. Lei and D.M. Lewis, Dyes and Pigments, in press.