Chemical Modification Of Chitosan Fiber And Its Dyeing Properties With Natural Dyes

Chitosan fiber as a novel functional fiber has a promising application prospect due to its good antibacterial activity, biological compatibility and biodegradation. However chitosan fiber has the serious weight loss problem under acidic processing conditions(e.g.,acidic dyeing and acid neutralization) in the wet processing. This decreases the content of chitosan fiber in its blends and the functionalities of its blends, and accordingly reduces its application value. In this work, in order to solve the aforementioned problem, chitosan fiber was first crosslinked by water-soluble diepoxy-, aziridine- and carbodiimide-based crosslinkers for the sake of enhancing its acid resistance. Subsequently, the crosslinked chitosan fiber was dyed using natural dyes with the aim of imparting multi-functional properties to it. The important conclusions were drawn as follows:(1) After crosslinked by the diepoxy crosslinker, chitosan fiber exhibited greatly reduced weight loss in acid solution due to remarkably increased acid resistance, and slightly improved the thermal stability and antioxidant activity. Crosslinking had no impact on the crystalline structure, moisture regain and direct and reactive dye adsorptions of chitosan fiber, but slightly decreased the dry tensile strength of chitosan fiber.(2) After crosslinked by the aziridine crosslinker, chitosan fiber exhibited obviously increased acid resistance, and slightly improved dry tensile strength and moisture regain.The thermal stability, crystalline structure, and direct and reactive dye adsorptions of chitosan fiber were not affected by crosslinking.(3) After crosslinked by the carbodiimide crosslinker, chitosan fiber displayed increased acid resistance, and slightly improved thermal stability and moisture regain. The crystalline structure of chitosan fiber and the adsorption capability for direct and reactive dye was not affected by crosslinking.(4) The extent of crosslinking formation between the molecules of chitosan fiber for three crosslinkers was in the following order: diepoxy crosslinker > aziridine crosslinker >carbodiimide crosslinker.(5) The equilibrium adsorption analysis showed that the Langmuir-Nernst isotherm was the best model to describe the adsorption behavior of lac dye, and Langmuir adsorption had greater contribution to total adsorption than Nernst adsorption. The electrostatic interactions between lac dye and chitosan fiber exerted a dominant role on the adsorption of lac dye on the crosslinked fiber. Lac dyeing imparted good antioxidant activity to chitosan fiber whereas the good inherent antibacterial activity of chitosan fiber was not affected.