Preparation Of PDMAEMA Cationic Modified Agent And Its Application In Salt-free Reactive Dyeing

The traditional dyeing process of reactive dyes requires a large amount of inorganic salt to eliminate the electrostatic repulsion between the cotton fabrics and the anionic reactive dyes,and to improve dye utilization.After dyeing,these inorganic salts have difficulty in degradation which increase the wastewater treatment burden.Cationic modification can improve the affinity between the reactive dyes and the cotton fabrics,and achieve salt-free dyeing.Aiming at the huge amount,the poor thermal stability,the high price of conventional small molecule modifier,and the uncontrollable molecular weight of macromolecule modifier,which is easy to cause poor levelness and low color fastness,dual stimuli-responsive PDMAEMA were designed and fabricated via ARGET-ATRP which had precise molecular structures and narrow molecular weight distribution.Cationically modified cotton fibers were prepared by multi-chemical cross-linking of cellulose molecules with silane coupling agents KH550 and PDMAEMA.PDMAEMA exhibited different charges under different p H due to the features of“protonation-disprotonation”of tertiary amine side groups.The modified cotton fibers were positively charged under the low temperature and acidic condition in the dyeing stage,which improved the adsorption capacity and the utilization rate of the dyes.The electrostatic attraction was weakened due to the neutral or electronegative charges under alkaline p H.Thus,the electrostatic attraction between the cotton fabrics and the anionic reactive dyes was weakened which has retarding and levelling effects.The synthesis and responsive properties of PDMAEMA,the characterization of the modified fabric,the dyeing process,and the thermodynamics of the dyeing were discussed in this article.The polymers with molecular weights of 12635,17899,23917,44876 were prepared by adjusting the ratio of monomer to initiator,which was 1:78,1:125,1:188,1:274;the fixed ratio of AA:PMDETA:Cu Br₂:EBi B was 0.5:0.25:0.05:0.1,and the temperature was 60°C.Moreover,the molecular weight distribution measured by GPC results was less than 1.2.It meant the molecular weight distribution was narrow.Modified cotton fibers with different graft ratios were prepared by adjusting the amount of the polymer,a fixed concentration of 5%KH-550 solution which was stirred in an ethanol:water=2:1 solutions for 1 h.the fixed mass ratio of solution:cotton fabric:triethylamine was 20:1:1.The surface tension test of the aqueous solution of the polymer showed that the polymer conformed to the surface activity exhibited by the environmentally responsive polymer as a function of the external environment.When p H was 5.5,the transmittance of the solution did not change with increasing temperature,the polymer had good water solubility,and the solution was clear and transparent;and the transmittance decreased rapidly from 100%to 0 in alkaline condition,demonstrating a good response performance of temperature.The polymer was characterized by ¹H NMR,FT-IR,EDS,FT-IR,SEM,XRD and Tg.Other properties of modified cotton fabrics such as whiteness,mechanical properties and wettability were investigated.The traditional dyeing process and the salt-free dyeing process of reactive dyes were discussed.The optimum grafting ratio was determined to be 15%.Taking the reactive red M-8B as an example,the best conditions were as follows:the dyeing temperature is 50°C,the p H value of the solution is5.5,the fixing temperature is 60°C,the amount of Na₂CO₃is 15g/L and it is added before heating.The results of salt-free dyeing showed that the K/S values of the modified cotton fabrics in reactive red M-8B,reactive blue KN-R and active golden K-2RA were increased by 28.7%,31%,36%compared with the unmodified fabric.Moreover,it had a good levelness,color fastness,and color shade.Isothermal dyeing rate curve of the three reactive dyes on modified fibers accorded with pseudo second-order kinetic model.The adsorption isotherm of the three reactive dyes on modified fibers followed to the Langmuir adsorption model.