Influence Of Electric Charge Effect Between Bleach Activators And Cellulose Fibers On Bleaching Process

The traditional industrial bleaching of cotton fibers are usually carried out in alkali ne solution of hydrogen peroxide at high temperature.The process causes extensive en ergy and water consumption,and the alkaline wastewater needs to be neutralized incre asing the burden on the effluent treatment plant.Bleach activator could react with per oxide to produce more reactive peracid,which is able to breach the natural colorants presenting in cotton fibers a lower temperature and make the bleaching process more efficient and save energy.The bleached fibers acquired considerable degree of whitene ss and less fiber damage.In this paper,sodium chloride was used as an auxiliary rea gent to investigate the effect of surface charge on fibers in bleaching process with per oxide and activators.Investigations were carried out on the absorption of three commo n bleach activators to cotton fibers so as to disclose the correlation between absorptio n and bleaching performance of activators.It was proposed to establish an rapid pad-s team bleaching system by using N-?4-?triethylammoniomrthyl?benzoyl?caprolactam chlori de?TBCC?as bleach activator,and the bleaching performance was optimized by facto rial experiments.In the first part of this paper,sodium 4-benzoyloxy benzene sulfonate?SBOBS?was prepared for use as a bleach activator.The experiment results showed that SBOBS could react with hydrogen peroxide to establish bleaching of cotton fibers in the pH range of 7-9 at 50?.The bleaching rates were improved when cotton fibers and partial cationic cotton fibers were bleached by the traditional hydrogen peroxide system with the addition of sodium chloride.Similarly,the bleaching rate of SBOBS-activated bleaching system was increased as well.However,the bleaching performance of TBCC-activated system decreased.This was ascribed to the presence of sodium chloride.It was surprising that such a negative effect of sodium chloride on the bleaching performance of the TBCC-activated system could not be eliminated by increasing the concentration of TBCC.This was possibly due to that sodium ions neutralized the negative charges on cotton fibers,and promoted the absorption of active ingredient with negatively-charged ions on the fiber surface.For the TBCC-activated bleaching system,the affinity of the peracid to cotton fibers was weakened so that the bleaching reaction was inhibition.These results indicated that there was a close relationship between the surface charge on fibers and bleaching performance.In the second part of this paper,the most representative three bleach activators,i.e.tetraacetylethylenediamine?TAED?,SBOBS and TBCC were selected to investigate the effect of absorption on bleaching performance.Experiment results showed that adsorption only existed between TBCC and fibers,and the bleaching performance of TBCC-activated system achieved the best performance.Hansen solubility parameters of three activators indicated that TBCC was more likely to close to negatively charged cellulosic fibers surface in solution.There were significant differences in the bleaching performance of the three activators with an increase in the concentration of chemicals.The bleaching performances of TAED and SBOBS increased solely with the chemical concentrations.However,when the chemical concentrations were high,it was difficult to improve the performance of TBCC-activated bleaching system.The experiment results showed that the bleached cotton fibers experienced flat or falling whiteness with increasing chemical concentrations.The reason was that TBCC and other produced cationic matters interacted with cotton fiber surface,which impeded the bleaching reaction.In the third part of this paper,for avoiding the adverse impact of the absorption between TBCC and fibers on the bleaching performance,the rapid pad-steam bleaching system was conducted based on the TBCC-activated peroxide system and optimized by discussing effect of factors.In order to further study the rapid pad-steam bleaching system,the performance of system was compared with traditional H₂O₂/NaOH system.Performance testing results showed that the rapid pad-steam system could provide cotton fibers with stable whiteness,lower fiber damage and acceptable dyeing properties by comparing with H₂O₂/NaOH system.