Application Of Chitosan Derivatives In Salt-Free Reactive Cotton Dyeing

The increasing consumption of cotton fabric dyed with reactive dyes is mainly due to their acceptable price,brightness of shade,wide colour gamut and excellent color fastness to laundering.However,low fixations,large requirement of electrolyte and heavy burden to processing are its conspicuous disadvantages.Based on this, chitosan was modified and applied to pretreating cotton fabric with the aim to improve the utilization of the reactive dyes and reduce pollution resulted from salt usage.Quaternized chitosan(CTA-CTS) and primary amine-substituted chitosan (AE-CTS) were synthesized and the structures were confirmed by IR,~1H NMR as well as the analysis of molecular weight.CTA-CTS,AE-CTS and hydrolyzed chitosan(COS) were applied to pretreatment of cotton fabric in salt-free dyeing process.The relationship between structures of chitosan derivatives and dyeing acceleration was investigated by the analysis of Zeta potential of chitosan derivatives and modified cotton fabrics.The quaternary ammonium groups of CTA-CTS and amino groups of AE-CTS and COS combined with hydrogen proton in dye solution were functional groups in improving the Zeta potential of the cotton fabrics,which resulted in a good dye fixation.The modified cotton fabrics were characterized by SEM,TG-DSC,Zeta potential as well as acid-base titration.The influence factors of pretreatment conditions on dyeing effect were also concerned.Dip-pad-bake process was employed in pretreatment of cotton fabric with CTA-CTS and AE-CTS.The optimum conditions for pretreating were established as follows:cotton fabric was treated with 10.0 g/L CTA-CTS(or AE-CTS) at a pH value of 6.0(or 6.4) for 10 min,and then dried at 80℃for 3 min,cured at 110℃for 3 min.It was found that the performances (including color,dye penetration,fastness and finishing properties) of dyed cotton fabric were close to or even higher than that of conventional dyeing.Moreover, chemical oxygen demand(COD) of dyeing effluent from zero-salt dyeing process was lower than conventional method. Dyeing mechanism was discussed.The adsorption isotherms of C.I.Reactive Blue 19 on modified cotton fabric were also similar to the Langmuir model.The pseudo-second order kinetic models fit very well with the dynamical behavior for the adsorption of dye RB 19 on modified cotton fabric.It is likely that the behaviors over the whole range of adsorption are in agreement with the chemisorptions mechanism being the rate-controlling step.The activation energy of the pretreated cotton fabric decreased,and this indicated that modification decreased the energy barrier of dye diffusion.Thereafter,the dyeing process could take place easily.