Study On Dyeing/Coloration Properties Of Meta-Aramid Pretreated By Organic Solvents

Due to the compact structure,meta-aramid fiber is difficult to dye by conventional dyeing methods.The dyeing problem of meta-aramid fiber is an industrial issue,which seriously hinders the development of meta-aramid fiber in the field of textiles and clothing.Pretreatment with organic solvents can swell the fiber,which is beneficial to the dyeing of the fiber.At present,there are still some problems in the dyeing of meta-aramid that pretreated by organic solvents,such as high pretreatment temperature,high dyeing temperature,great damage to the mechanical properties of dyed fabrics,and large salt consumption when using cationic dyes.This paper systematically studys the dyeing/coloration properties of meta-aramid fiber pretreated by organic solvents.The damage of the mechanical properties of the dyed aramid fabric reduces effectively,while the dyeing performance keeps well,through optimizing the pretreating process and dyeing condition.Subsequently,a coupling coloration of meta-aramid fiber by using weakly basic aromatic amine diazonium salt is described.A coloration mechanism through in situ formation of azo chromophore is revealed.Then,a highly active coupling component is introduced into the fiber by chemical modification.As a result,the color of meta-aramid fabric by coupling coloration has been effectively expanded.The results of this paper provide a new idea for the dyeing/coloration of aramid fiber that pretreated by organic solvents.The main research contents are as follows.1.Meta-aramid fiber is pretreated with organic solvents,and then dyed with disperse dyes.The pretreating and dyeing conditions are optimized,and the effects of solvent pretreatment on the mechanical properties and dyeing properties of meta-aramid fiber are studied.The results show that the pretreatment of meta-aramid with organic solvent can effectively improve the dyeing properties of meta-aramid,but also cause shrinkage of meta aramid fibers,therefore reducing the mechanical strength of the fabric,and damaging the fiber surface.Properly decreasing the pretreating temperature and dyeing temperature can effectively reduces the damage of mechanical property while maintaining the satisfactory dyeing performance.In the optimized pretreating process and dyeing condition,meta-aramid fabrics is pretreated in dimethyl sulfoxide(DMSO)at 55 ℃ for 30 min,and dyed at 80 ℃ for 60 min.Under the optimized condition,the shrinkage of dyed meta-aramid fabric dereases to less than 10%,while the breaking strengths range from 818 to 1110 N.Compared with anthraquinone and heterocyclic disperse dyes,azo disperse dyes are more suitable for low-temperature pretreating and low-temperature dyeing of meta-aramid fiber.In particular,when meta-aramid fiber is dyed with C.I.Disperse Red 167 at 1% owf level under the optimum condition,a dye uptake of 95% and a color depth of 7.2 are obtained for the dyed fabric.Also,the color fastnesses to soaping,rubbing and sublimation can reach above grade 4.2.The meta-aramid fabric pretreated by organic solvents is treated with weakly basic aromatic amine diazonium salts.The pretreating process and coloration condition for meta-aramid fiber are optimized.An optimum process for coupling coloration of meta-aramid fiber with diazonium salts is established.The variation of color depth of fabrics with diazonium salt dosage and coloration time is explored.The influence of coupling coloration process on the mechanical properties of fabrics is studied,and the coupling coloration mechanism of meta-aramid fiber is deeply revealed.The results show that the pretreated meta-aramid fabric shows deep and firm color under the action of weakly basic aromatic amine diazonium salts.In the optimized coloration process,the meta-aramid fabric is colorated with a diazonium salt of 0.4 mmol/g at room temperature for 2 h.Methanol is selected as a penetrant(the volume ratio of methanol to diazonium salt solution is 1∶1).It is found that all the diazonium salts prepared from4-nitroaniline derivatives have good coloration performance.Among them,the aramid fabric colorated with 2-bromo-4-nitro-6-cyanoaniline diazonium salt is brown,with a K/S value of 17.7,which has good extraction resistance to organic solvents.The color fastnesses to soaping,rubbing and sublimation can reach higher than grade 4.The existence of a large amount of acid in the coloration process will decrease the mechanical strength of the fabric.The use of diazonium salt aqueous solution instead of acid solution can effectively reduce the damage of the mechanical property of the fabric.The study of coloration mechanism shows that both the middle and end of meta-aramid macromolecular chain may be the coupling reaction sites.Among them,the highly active terminal m-phenylenediamine is the preferred site for coupling reaction,which produces azo chromophores with dark color.However,the quantity of the terminal m-phenylenediamine is limited.Correspondingly,the large quantity of the middle m-phenylenediamine unit is the main site for coupling reaction and the main source for color of meta-aramid fabric,although its activity is slightly lower.3.Two aniline derivatives D1 and D2 containing diazirine structure are designed and synthesized,and applied to the modification of meta-aramid fiber.The pretreatment,modification and coloration process of meta-aramid fiber is designed and optimized.In the optimized modification process,meta-aramid fiber is firstly immersed in methanol solution of aniline derivatives with concentration of 4 g/L for 3 h,then dried and cured at 140 ℃ for 30 min.After introducing the highly active coupling components into aramid fiber,meta-aramid fabrics with yellow,red and blue colors are successfully obtained by using p-chloroaniline diazonium salt,2-chloro-4-nitroaniline diazonium salt and 2-amino-5-nitrothiazole diazonium salt.Therefore,the color category of pretreated meta-aramid fiber by using coupling coloration method has been effectively expanded.Among them,meta-aramid fabric colorated by p-chloroaniline diazonium salt exhibits yellow with a K/S value of 16.0 and a fixation value of 98.8%.The meta-aramid fiber colorated by 2-chloro-4-nitroaniline diazonium salt exhibits red with a K/S value of 13.9and a fixation value of 90.5%.The meta-aramid fiber colorated by2-amino-5-nitrothiazole diazonium salt exhibits blue with a K/S value of 20.4 and a fixation value of 87.4%.All the color fastnesses to soaping,rubbing and sublimation for these colorated meta-aramid fabrics are higher than grade 4.