The Improvement Of Dyeing Property Of Disperse Dyes In PLA Fiber

Polylactic acid(PLA) fiber is a new type of biodegradable synthetic fiber, and it has the good performance like other synthetic fibers in the market. Unlike other synthetic fibers, PLA fiber has a special property that it can be biodegraded by the environment. Hence PLA fiber has been extended to other aspects of textile field, which brought the new challenges in the dyeing and finishing technology at the same time. PLA fiber is mainly dyed with disperse dyes, but the dyeing uptake of disperse dyes on PLA fiber is lower than that on PET fiber. So it is difficult to get deep color for the PLA fabrics in the production. There are not the UV-absorbing groups in the PLA structure, and the fabric dyed with disperse dyes will fade easily by sunlight, so improving the color fastness to light of PLA fibrics has become a problem demanding urgent solution. Although there have been a lot of studies on dyeing and finishing performance of PLA fibre, most of them were the improvement of PLA dyeing process and primary theoretical analysis, the low dyeing uptake and the poor color fastness to light of PLA fiber were not solved effectively. And the quality of PLA fiber after dyeing and finishing can not be assured in practical production. Therefore the objective of this paper is to improve the dyeing properties of the PLA fibers through developing a dyeing agent or dyeing technology that can increase the dye-uptake and the color fastness to light of disperse dyes on PLA fibers.This paper mainly chose different esters to adjust and control the fiber structure and use surfactant to improve the dyeing property of disperse dye to PLA fibers. By determining the optimum dosage of ester and the surfactant, an efficient PLA accelerating agent was developed. Meanwhile, the effect and the mechanism of accelerating agent on dyeing behaviour of disperse dyes on PLA fiber was studied. The improvement of ultraviolet protection property of PLA fabric dealt with Ultraviolet Absorbents was also studied. By applying Ultraviolet Absorbents to PLA fabric together with disperse dyes, the effect of Ultraviolet Absorbent on color fastness to light of PLA fabric was investigated. Finally, the appropriate Ultraviolet Absorbents were screened out to use for preparing the light fastness accelerating agent, the optimization applied process was developed.This paper selected some esters according to the solubility parameter close to the PLA fibers and mainly researched the effect of acetic esters on dyeing performance of PLA fiber. The results showed that n-amyl Acetate could improve the dyeing property of the PLA fiber, and the dyeing uptake of disperse dyes and K/S value of PLA fibric had been improved greatly. The optimum dosage of n-amyl Acetate was 6ml/L., it had no obvious effect on mechanical property of PLA fiber, color fastness and color consistency. However, n-amyl Acetate is insoluble in water, so dyeing asymmetry phenomenon happened on some disperse dyes. What was more, the dyeing uptake of disperse dyes could be improved further. So the effect of several kinds of surfactant on dyeing uptake of disperse dyes on PLA fiber was studied. The results of the experiment showed that cationic surfactant DDAB had the best accelerating effect, it could increase the dyeing uptake of disperse dyes obviously when its dosage was 0.5g/L, but the dyeing asymmetry phenomenon also happened because of the infusibility.The choosing of emulsifier was close to stability of the accelerant agent directly, Span 80 was selected as the emulsifier of dyeing accelerant, and the PLA dyeing accelerating agent was developed composed of 5mL/L n-amyl Acetate, 0.5g/L DDAB, and 2.5%Span 80 (the volume content compare to the n-amyl Acetate), emulsifying temperature was 40～60℃(rotate speed 10000r/min). The accelerating agent was environment-friendly and stable. It could improve the dyeing uptake of disperse dyes and K/S value of PLA fabric., But it had little effect on color fastness, as a whole, color fastness was above 3～4 grade besides the light color fastness.The experiment tested the diameter of PLA fiber after it was dealt with different acetic ester, and the effect of n-amyl Acetate and DDAB on microstructure of PLA fiber was studied through FTIR and DSC analysis. The results showed that: swelling behavior happened in the PLA fiber treated with acetic ester except methyl acetate. There was some relationship between the chain length and swelling behavior plasticizing effect. Longer the chain length of the esters was, easier the dyes enter the inside of PLA fiber. The n-amyl Acetate and DDAB could not change the molecular structure of PLA, but had effect on its crystallinity, especially n-amyl Acetate. It had good plasticizing effect on PLA fiber and decrease the crystallinity.The effect of the ultraviolet absorbents on dyeing performance with disperse dyes together and ultraviolet protection property of the PLA fiber were investigated. The results showed that the dyeing uptake of ultraviolet absorbents and disperse dyes were very low when there was no accelerating agent in the dye bath. When adding the accelerating agent in the dyeing liquor, the dyeing uptake of ultraviolet absorbents and disperse dyes could increase to 90%. All of the four ultraviolet absorbents in this paper had good effect on ultraviolet protection property of PLA fabrics, especially using the accelerating agent, the UV transparence rate, UPF and UV protection evaluation were all perfect. The ultraviolet absorbents could decrease the color difference after solarization, and improve the color fastness to light of PLA fabric. The ultraviolet absorbent which had the best effect on the color fastness to light was UV-531 and its dosage was 2% (o.w.f).