Protection Of Pulp Viscosity In Ozone Bleaching

In the past two decades,ozone has been paid more and more attention to pulp bleaching.However,the ozone bleaching of pulp has not been widely used in the industrial application.One of the most important reasons is that the pulp viscosity decreases greatly due to the serious destruction of carbohydrate by ozone in the ozone bleaching.In this study,the ozone bleaching of pulp with different consistency was simulated by a laboratory device self-designed.The viscosity,crystallinity and carboxyl content of pulp were studied,the result indicated that the properties of pulp fiber after bleaching were affected by the consistency of pulp during ozone bleaching.The ozone bleaching of low-consistency pulp had the highest selectivity and the least damage to carbohydrates.The optimized reaction condition was fixed at: pulp concentration 3%,ozone dosage 1%.The former listed conditions resulted in brightness: 39.6% ISO;Kappa value: 12.6;viscosity: 743 m L/g.The viscosity protectant of pulp during ozone bleaching was studied with low-consistency pulp.Meanwhile,the effects of agents such as oxalic acid,tert-butanol,magnesium sulfate and chitosan as a new viscosity protectant in the ozone bleaching were compared.Furthermore,the preliminary discussion of the protective mechanism of chitosan was conducted through a series of characterizations.Such as the physical properties,crystallinity,infrared,and carboxyl content.Results showed that the physical properties of paper were improved,the tensile strength,tearing and burst index of pulp was increased by 54.45%,15.79% and 29.89% respectively.In addition,the pulp crystallinity was risen,the carboxyl group content was decreased.Meanwhile,the selectivity of delignification was increased,and the protection against carbohydrates was enhanced.Among the selected viscosity protectants,the chitosan possessed the best effect on improving the property of bleaching pulp.We could get the bleached pulp with brightness: 42.9 %ISO,Kappa value: 11.7,and viscosity: 796 m L/g.On the basis of the previous comparative study,the paper further discussed the ozone bleaching with chitosan as protective agent.Single factor experiments were carried out on the molecular weight,degree of polymerization(DP)and concentration of chitosan.On the basis of single factor experiment,a three-factors,three-levels orthogonal experiment was designed with the degree of chitosan deacetylation(A),the concentration of chitosan(B)and the molecular weight of chitosan(C).Meanwhile,the response surface analysis was performed by characterizing the test results with pulp viscosity,whiteness,and Kappa values.The results showed that the best condition were that deacetylation degree: 95%;concentration: 4%;molecular weight: 90000;additive: chitosan,the mean values of viscosity,whiteness and kappa value of the pulp after bleaching were 806 m L/g,44.3 %ISO and 10.71,respectively.Finally,the crystallinity,specific surface area and adsorption behavior of different pulp were studied.The results showed that the specific surface area was increased after ozone bleaching,which was conducive to the fiber binding.After the chitosan was added,the protective effect on carbohydrate was enhanced.The Zeta potential demonstrated that the adsorption capacity of fiber chitosan was decreased due to the chitosan covering on the cellulose surface.The FTIR spectra and the microscopic analysis of SEM indicating that the addition of chitosan had a positive effect on the protection of pulp viscosity.