Study On Indigo Dyeing Of Polylactic Acid Yarn Based On Application Of Denim Fabric

With the increasing shortage of oil resources,new environment-friendly bio-fiber materials have been widely used in the denim industry,because of the characteristics of white weft and color warp of denim fabric,yarn dyeing is the focus of research.As a new biodegradable and pollution-free bio-based fiber,compared with cotton,poly（lactic）acid（PLA）can be spun filaments and it can save energy when it compared to polyester,it is of great significance to promote the application of polylactic acid in denim fabrics.In this paper,the optimum dyeing parameters of PLA yarn with indigo vat dye were studied by analyzing the structural characteristics of polylactic acid molecule and indigo molecule.The dynamic parameters of dyeing kinetics and thermodynamics of indigo dyeing PLA yarn were analyzed by experiments.The adsorption and resolution process of indigo vat dye on the surface and inside of PLA yarn was investigated.In addition,the PLA yarn was modified by lipase to explore the effect of lipase on the hydrophilicity and physical and mechanical properties of PLA yarn.At the same time,the effect difference between synthetic indigo and natural indigo dyed PLA yarn was explored.Firstly,an orthogonal experiment was designed to explore the influence of indigo concentration,sodium hydroxide concentration and insurance powder concentration on the dyeing effect of PLA yarn.The optimal concentration ratio of indigo: insurance powder: sodium hydroxide was 1∶1∶1.5.The effects of dyeing temperature,dyeing solution p H,dyeing time and dyeing times on the dark dyeing and physical and mechanical properties of PLA acid yarn were investigated by using the optimal ratio obtained by orthogonal experiment.The results showed that when the dyeing temperature was 110℃,the p H of dyeing solution was 5,the dyeing time was 40 min,the dyeing times was 3 times,the K/S value was 11.43,when the volume ratio of paraffin wax to indigo dye was 3∶2,the K/S value was 13.34,and the color fastness grade of yarn was 3-5.Secondly,different dyeing temperature gradients and indigo concentration gradients were designed to dye PLA yarns,and the dyeing kinetics and thermodynamics of PLA dyed by indigo were investigated successively.The experimental results showed that the dynamic saturated adsorption capacity,half-dyeing time,dyeing rate constant and other dynamic parameters in the dyeing process were obtained,and the adsorption model analysis of dyeing thermodynamics showed that the adsorption type of PLA yarn dyed on indigo was closest to the Nernst adsorption model.The changes of dyeing affinity,dyeing heat and dyeing entropy at different dyeing temperatures indicate that the dyeing of indigo on PLA yarn is an exothermic reaction,and the optimal dyeing temperature should be controlled between 100℃ and 110℃.Finally,different lipase treatment conditions were used to treat PLA yarns to explore the effects of lipase treatment on hydrophilicity and physical-mechanical properties of PLA yarns.The results showed that lipase treatment time of 3 h,treatment temperature of 55 ℃,treatment concentration of 0.8 g/ L had the greatest influence on the strength of the yarns,and the hydrophilicity increased the most.Through synthetic indigo and natural indigo dyeing of PLA yarn treated with lipase,the lipase treatment on yarn dark dye on the feasibility of PLA were explored,at the same time,the dyeing effect of synthetic indigo and natural indigo on polylactic acid was analyzed The results showed that under the same dyeing conditions,the dyeing effect of synthetic indigo was better than that of natural indigo,but the damage to the physical and mechanical properties of PLA yarn was greater than that of natural indigo.For natural indigo to dye PLA,sufficient insurance powder and sodium hydroxide are beneficial to the optimization of natural indigo to dye PLA yarn.