The Study, Preparation, Application And Mechanism Of Improving Agent Of Light Fastness For Coloured Polyester Fabrics

With the rapid development of China’s economy and society, rapidly upgrade of people’s living standards, and the modernization of national army, the increasingly higher demand of light fastness of textiles in many fields, such as clothing including military uniforms, house hold and car interior decorating textiles, has been required. On the other hand, the increasing amount of ultraviolet radiation caused by the deteriorating of global environment not only seriously hurts the health of human being, but also exacerbates the discoloration of clothing and decorative textiles in the process of use.Polyester fiber has now been the most widely used textile fiber because of its ruggedization. China has become the greatest producer and consumer of polyester fiber in the world. Although the polyester fabrics dyed with disperse dyes generally have high light fastness, discoloration could still be happened in the using process caused by variety of factors. At present, to meet the demand of higher light fastness of polyester textiles, some light stabilizing auxiliaries are still needed to be added in the production to enhance the light fastness of dyed textiles.When the dyes in the coloured fabrics are in the excited state due to an absorption of higher energy UV radiation, the photochemical reaction may occur leading to a colour fading or hue changes. The occurrence of such changes may also be influenced by the textile substrate. The disperse dyes taken up on polyester fabrics may easily be decoloured in the wavelength range in which the most serious degradation of polyester matrix happens with the photochemical reaction. This wavelength range should be between 280nm and 340nm in the UV region and 310nm is said the most sensitive wavelength.UV absorbers are a class of substance which can strongly absorb ultraviolet radiation and then release out the absorbed energy in the form of less destruction. With the application of UV absorbers in the polyester fabrics, the photochemical reaction on fabric substrates and the dyes caused by ultraviolet radiation could be avoided. The fabric substrates and the dyes can be protected and the light fastness can be improved.Therefore, the UV absorbers can be used as the active ingredient of the improving agent of light fastness for polyester fabrics and applied in one bath dyeing with disperse dyes after the UV absorbers are grinded and dispersed to stable dispersion. The UV absorbers chosen should have strong UV absorption and high uptake on the polyester fabrics. For the purpose of development of an improving agent of light fastness for polyester fabrics, a triazine type UV absorber was synthesized, a series of commercial benzotriazole ultraviolet absorbers and a benzophenone UV absorber were chosen to be as the active ingredients of the improving agents of light fastness. In order to choose the suitable UV absorbers for the development of the improving agent of light fastness, the absorption properties, the dyeing properties and the kinetics and thermodynamics of dyeing onto polyester, the interaction of UV absorbers and dyes in the one bath dyeing, the effect and related regularity of the improvement on light fastness by these UV absorbers were systematically studied.In the process of the synthesis of triazine type UV absorber, two-step reactions were occured:(1) cyanuric chloride reacted with m-xylene in the catalysis of anhydrous aluminum chloride to generate intermediate 2,4-bis(2’,4’-dimethylphenyl)-6-chlorin-1,3,5-triazine; (2) the intermediate reacted with resorcinol in the catalysis of anhydrous aluminum chloride to generate 2,4-bis(2’,4’-dimethyl-phenyl)-6-(2’,4’-dihydroxyphenyl)-1,3,5-triazine as the ultimate product. The intermediate and ultimate product were characterized to confirm the synthesized product as the target absorber UV-T, through the test of melting point, the analysis of infrared absorption spectrum,1HNMR, mass spectrometry and UV absorption curve of the target product. The molecular weight of UV-T is 397.0. There is a strong absorption in the range of 260-360nm and an absorption peak exists at 286nm. The molar extinction coefficient at maximum absorption wavelength of UV-T is 2.82×104 cm-1·mol-1·L.Then, UV-1 was used as the example to be grinded and dispersed through the experiments with the single-factor analysis and orthogonal designed experiments considering various parameters, forming an optimum process conditions of preparing a stable dispersion liquid of UV absorber as below:content of UV absorber 28%, the amount of dispersant D-1 10% relative to the amount of UV absorber, super-dispersant 2% of the amount of UV absorber, temperature of cooling water 15℃, grinding sand filling rate 50%, and the grinding time 2h.In order to study the high pressure and high temperature dyeing properties of UV absorber on polyester systematically, the uptake test method with DMF extraction of UV absorber from the polyester was established through the analysis of the temperature, time of extraction, the selection of reference and other factors. The uptake test methods with double-wavelength spectrophotometry for the dyeing of UV absorber and disperse dyes in one bath was established by selecting the appropriate analytical wavelength and reference wavelength, and thus the interference of disperse dyes to the uptake of UV absorbers was eliminated.In the study, the influences of the structures of benzotriazole UV absorbers on the UV absorbing capacity were not only analyzised, but also the differences of UV absorption characteristics among the triazine, benzotriazole, and benzophenone UV absorbers were compared. In the dyeing of UV absorbers to the polyester, temperature was found playing a very important role. The dyeing of UV absorbers on polyester was similar to the dyeing of disperse dyes following to the free volume model, and the uptake of UV-absorber went up quickly when the dyeing temperature reached 130℃. The influence of size of UV absorbers particles in dispersion on the dyeing properties was also found, the smaller of the particle the higher of the uptake. Among benzotriazole UV absorbers, the one with smaller molecular weight, smaller molecular volume and simpler structure had higher dyeing uptake on polyester. Among UV absorbers of different types, UV-7 with linear molecule had highest uptake on polyester fabric and their comparison was UV-7> UV-T> UV-3. Comparing the UV transmittance and UPF of polyester fabrics dyed with benzotriazole UV absorbers and the different types of UV absorbers, the uptake of UV absorber was found playing a major role. The UV absorbers with high uptake on polyester and strong UV absorption can make the polyester fabrics greatly absorb UV radiation. UPF values of the fabrics dyed with the UV absorbers showed as UV-7>UV-T>UV-3. However, despite the hue of fabrics dyed with UV absorbers and disperse dyes in one bath did not change basically, the uptakes of both UV absorbers and disperse dyes on polyester fabrics declined in a certain extent compared with that on solely dyeing respectively.According to the hyperbolic equation adopted by Vickerstaff and Hill equation, the kinetic parameters, such as equilibrium uptake amount, constant of dyeing speed, half-dyeing time and diffusion coefficient of the five selected typical UV absorbers dyeing on polyester were calculated from the dyeing speed. The adsorption isotherms of the five selected typical UV absorbers dyeing on polyester were drawn at 110℃and 130℃, showing that the dyeing of UV absorbers on polyester belonged to the Nernst-Model which was similar to the dyeing of disperse dyes. The dyeing affinity, dyeing thermal value and dyeing entropy value of UV absorbers on polyester were also analyzed.For the UV absorbers of lower uptakes with large molecular, comparatively complex structure, plasticizers and solubility improving agents which once used in the dyeing of disperse dyes were tried to enhance the uptakes of UV absorbers. The n-Amyl Acetate was proved having the ability of improving uptake of UV absorbers on polyester. With the solubility improving effect of the new-type Gemini surfactants, an auxility with the formulation of n-Amyl Acetate and Gemini surfactants can improve the uptakes of UV absorbers with large molecular, comparatively complex structure on polyester in the one bath dyeing with disperse dyes, while the uptakes of disperse dyes on polyester were reduced further.The light fastness improving agent made of UV absorbers as the active ingredient with an optimized process of grinding and dispersing can be used in the dyeing on polyester with disperse dyes and made the light fastness of coloured polyester fabrics obviously improved. The light fastness improving agent made of UV-3 could make the improvement of light fastness more greatly, which enhanced light fastness up to 1.5 grades for the lower light fastness dyes originally and about 0.5 grade for the higher light fastness dyes originally. The light fastness improving agent made of UV-7 and UV-T as the active ingredient could improve the light fastness obviously for the lower light fastness dyes originally and weak for the higher light fastness dyes originally.The effect of the light fastness improving agent made of UV absorbers as the active ingredient was determined by both the absorbance at the sensitive wavelength of polyester 310nm and the uptake on polyester mainly. The product of these two factors could be prospective parameter for the improvement of light fastness from the light fastness improving agents made of UV absorbers as the active ingredient. In a word, the design, preparation and application of the light fastness improving agent for polyester could be made according to the results theoretically.