Synthesis And Properties Of Water-Soluble Chitosan-Polymeric Dyes

Chitosan-polymeric dyes are the ideal functional polymers, which can be synthesized using grafting and modification. The polymeric dyes have not only the merits such as high strength, easy to film-forming, solvent-resistance and migration-resistance, but also the biocompatibility and eco-friendliness performance of chitosan. In this work, the water-soluble chitosan-polymeric dyes were synthesized by the etherification of the reactants from chitosan and reactive dyes using chloroacetic acid. The modification enhanced greatly the water-solubility of polymeric dyes and expanded their application fields. The research results were as follows:The factors influencing the reaction of chitosan and the vinylsulphone reactive dyes were temperature and pH. The reaction degree increased above the temperature above 60℃. Under acidic conditions, reactive dyes exhibited the high degree of absorption but the low degree of reaction on chitosan. Under natural to alkaline conditions, the degree of reaction was high, but the extent of the reaction of reactive dyes with the amino groups in chitosan decreased with the increase in pH. The FTIR analyses showed that the covalent bonds were formed between reactive dyes and chitosan. The optimum reaction of reactive dyes with chitosan should be performed under pH 7 and 60-80℃in order to increase the degree of the next etherification reaction.The water-soluble chitosan-polymeric dyes were obtained by the etherification of the reactants from chitosan and reactive dyes using chloroacetic acid at 55℃and under strongly alkaline medium. The FTIR analyses demonstrated the existence of the carboxymethyl groups in the synthesized dyes. The other instrumental analyses indicated that the crystallinity and thermal stability of water-soluble polymeric dyes decreased in comparison with chitosan.The water-soluble chitosan-polymeric dyes exhibited very excellent solvent-resistance and high water-solubility. The polymeric dyes had the characteristic of amphoteric polyelectrolytes with the isoelectric point approximately from 6.2 to 7.5. Their dilute solutions followed Lembert-Bill's law and the specific conductance of the solution had good linear relation with the concentrations of the dyes. The intrinsic viscosity of dye solution reduced obviously in comparison with chitosan.In addition, another new water-soluble chitosan-polymeric dye was prepared by the etherification using ethylene chlorohydrin.