Effect Of Enzymatic Treatment On The Wet-End Characteristics Of Bleached Softwood Pulp

Pulp and papermaking industry is an energy-intensive processing industry,in which energy consumption consists about 18%～25% of the manufacturing cost. Beating and refining of kraft pulp requires substantial energy, about 15%～18% of the total electrical energy needed for producing paper. Therefore, decrease of the energy consumption by enzymatic beating is of far-reaching significance. Enzymatic beating using enzymes to pre-treat pulp before beating can not only active the fiber surface but also promote the fiber water-absorbability and fibrosis, which facilates the beating process by saving specific energy consumption.Wet-end chemistry played a crucial role on the machine runnability and paper quality. The study of the effect of enzymatic treatment on the wet-end characteristics of bleached softwood pulp contributed to the reasonable control of the wet-end chemistry and it would be helpful to achieve high efficiency and save energy.The factors which influence the enzymatic beating were discussed and the optimum conditions were choosed in the paper. The FQA, ESEM, XRD were used to analyze the effect of enzymatic beating. The zeta potential tester and the charge titration instrument were also used to analyze the wet-end charge in order to obtain the effect of enzymatic beating on wet-end characteristics.Firstly, cellullase was used to treat bleached softwood pulp prior to beating and then the factors of the enzymatic beating were discussed. The optimum applications were as follows: the dosage of 0.5 ECU·g^-1 dry pulp, the pH value of 7, the temperature of 55℃and the time of 60 min. The results showed that enzymatic beating could promote the fibrillation and increase the specific surface of fibers and swelling ability, and the beating capability was improved. Compared to the control pulp, the content of carboxyl and fines of the enzymatic beating pulp was lower, but the average fiber length was longer. Moreover, the dissolved charge and the zeta potential were a little lower. The amount of cationic poly acrylamide absorbed and the retention of calcium carbonate were increased by enzymatic beating and the size efficiency was improved. However, cellullase pretreatment could reduce the degree of the polymerization of the fiber and lead the breaking length to drop. Cellulase pretreatment prior to beating caused the crystallinity to increase slightly compared to the enzymatic treated pulp which was not beated, but the crystallinity of the enzymatic beating pulp changed a little compared to the control pulp. Secondly, xylanase was used to treat the pulp prior to beating, and the factors of enzymatic beating were discussed. The results demonstrated that the optimum applications of xylanase were as follows: the dosage of 0.5 AXU·g^-1 dry pulp, the pH value of 7, the temperature of 55℃and the time of 60 min. The changes of fiber characterics, zeta potential, retention efficiency and size efficiency caused by xylanase pretreatment were similar to those of the cellulase, but the effect was not more remarkable than that of the cellulase. The dissolved charge of the xylanase-pretreated pulp increased with the increase of the dosage of enzyme. Enzymatic beating had little influence on the degree of the polymerization of the fiber but increased the breaking length of paper, which was different from the cellulase. However, xylanase pretreatment resulted in the slight increase of cellulose crystallinity, from 70.58% (control pulp) up to the 72.68%.Finally, the enzyme which consisted of a different proportion of cellulase and xylanase was used to study the effect of enzymatic beating. The results demonstrated that the changes of fiber characterics, wet-end charge, etc. caused by mixed enzyme pretreatment were also similar to those of the cellulase, but it was not remarkable as that of the cellulase. Enzymatic beating reduced the degree of the polymerization of fiber and the breaking length of paper slightly with the increase of cellulase dosage. When the dosage of cellulase and xylanase was 0.2 ECU·g^-1 and 0.3 AXU·g^-1 respectively, the mixed enzyme pretreatment led the crystallinity of cellulose to increase, from 70.58% (control pulp) up to the 72.15%. The cooperated action of the mixed enzyme was better than that of the cellulase or hemicellulase when the whole factors were taken into account.