Preparation Of Cationic Polymers With Low Polymerization Degree And Their Application In Salt-free Dyeing

Preparation and application of cationic agents is the key to realize the salt-free dyeing with reactive dyes for resolving the problems of the low efficiency of reactive dyes and the environmental pollution of the inorganic salt discharged in the conventional dyeing. The cationic agents reported previously showed many problems, such as poor penetrability of reactive dyes in cotton fibers induced by the pretreatment of cationic agents with large molecular weight; and the darkened shade of dyed fibers, the decreased colorfastness or mechanical properties of the fibers, which were mainly caused by the staining of the hydrolyzed dyes on cotton. In order to solve the problems above, we prepared three cationic polymers with low polymerization degree as salt-free dyeing agents, which included cationic polyacrylamide with quaternary ammonium groups, tertiary amine cationic polyacrylamide and poly(acryloxyethyl trimethylammonium chloride). The synthesis conditions of the cationic agents with low polymerization degree, the application process of the cationic agents, the mechanism of salt-free dyeing and the properties of dyed fabrics were all studied systematically to find out a favorable agent for salt-free dyeing.Cationic polyacrylamide with quaternary ammonium groups was applied to the pretreatment of cotton due to its stable chemical properties and suitable molecular weight. In this part, in order to control the polymerization degree of the cationic polymer, sodium formate (4.05 g/L) and hydroquinone (2.5×10-5 mol/L) were added in the polymeric reaction as the chain-transfer agent and the inhibitor agent, respectively. Application of the cationic agent showed that the affinity between the cationic fabric and the reactive dye was increased and the color yield of the cationic dyed fabric was enhanced. In addition, the time reaching the dyeing equilibrium was shorter, the mechanical properties of the dyed fabrics were not affected by pretreatment and the dyed cotton still presented brilliant color.For the purpose of the improvement of the decreased colorfastness properties of salt-free dyeings, tertiary amine cationic polyacrylamide was used as a new salt-free dyeing agent due to its characteristics that it showed positive charge only under acidic conditions. We studied the salt-free dyeing results with tertiary amine cationic polyacrylamide with different molecular weight and different cationic degree. The pretreatment and salt-free dyeing conditions were also investigated. The effect of the structures of the reactive dyes on both the salt-free dyeing results and the properties of the dyed cotton were investigated in this study. The optional pretreatment and salt-free dyeing conditions were drawn out as follows:the cotton was dip-padded with 2% of tertiary amine cationic polyacrylamide solution (molecular weight,1.12×104 g/mol; cationic degree,46.8%), and then baked in the baker at 100℃, after pretreatment, the cationic cotton was dyed at room temperature and dip-padded with 15 g/L of sodium carbonate solution, and then steamed for dye fixation within 10 min. Finally, K/S value of the dyed cationic fiber was higher than that of the conventional dyeing.Our research work indicated that the colorfastness properties of the dyes were much affected by the staining of the hydrolyzed dyes on cotton. And these hydrolyzed dyes were difficult to be washed off from cotton in common soap-off procedure. In this study, poly(acryloxyethyl trimethylammonium chloride) was prepared for pretreatment cotton in order to solve the problem of colorfastness. Within its molecules, quaternary ammonium groups were connected with carbon chain backbone through ester bonds, and the ester bonds could be broken off in the alkaline condition. The synthesis conditions, the properties in aqueous solution and the application conditions of poly(acryloxyethyl trimethylammonium chloride) with low polymerization degree were all studied. We also investigated the mechanism of salt-free dyeing process and the fastness properties of the dyed cotton. The salt-free dyeing results were favorable when the cotton fiber was dipped into poly(acryloxyethyl trimethylammonium chloride) solution (molecular weight,8.7×103 g/mol) and the reactive dyes were fixed on the cationic fiber by steaming. In comparison with the conventional dyeing, the dyeing fixation of reactive dye was increased by 5-10% in the salt-free dyeing, and the cationic dyed fabrics could realize leveling dyeing and the penetrability of the dyes were good. Moreover, the fastness properties of the cationic dyed fabrics were equal to or higher than the results of the conventional dyeing.In this paper, it showed that the cationic dyed fabrics all realized levelness and penetrability. Compared with the conventional dyeing, the uptake of reactive dyes was increased on the cotton pretreated with all three cationic agents with low polymerization degree. Poly(acryloxyethyl trimethylammonium chloride) containing hydrolysable ester bonds could be regarded as an improved cationic agent of cotton for salt-free reactive dyeing, because application of it solved the problem of the decreased fastness properties, which was caused by the staining of the unfixed reactive dyes after dyeing.