Application And Preparation Of Cationic Modified Microfibrillated Cellulose For Improving Bctmp Properties

In recent years, high yield pulps(HYP), especially bleached chemi-thermo-mechanical pulp(BCTMP) and alkaline peroxide mechanical pulp(APMP) are of great concern due to their low furnish cost, high bulk, and good optical properties. However, the retained lignin in pulping process hinders the interfiber binding resulting in poorer strength properties than those of chemical pulps. To improve the strength properties of BCTMP without affect its high bulk, cationic microfibrillated cellulose (CMFC) were prepared by a combination of cationic pretreatment and homogenization in this study. Further, the cationization process of CMFC was optimized, then different properties of CMFC were applied in strengthening sheet and improving fines retention of BCTMP.The CMFC, fiber mean length600-1300nm, DP value of340～570was prepared by a combination of cationic pretreatment and homogenization under the following preparation conditions:the alkalization temperature30℃, the alkalization time45min, the etherification temperature50℃～℃, the time for etherification150-180min, the dosage of CHPTAC and anhydroglucose units in cellulose molar ratio of0.8, the molar alkali to CHPTAC ratio of2.0, homogenenization10pass.The BCTMP sheets strengthening study demonstrated that with the addition of712μeq/g SCD of CMFC, the tensile index,burst index, tear index of BCTMP sheet respectively increased by52.7%,73.9%,22.1%, the bulk decreased by2.21%just at a2.5%dosage. While with the same dosage MFC, the corresponding values were17.1%,22.8%,19.2%and1.71%。It was found that the addition of CMFC had positive effects on strength properties including tensile, burst, tear strength of BCTMP. And, at the same enhancement of BCTMP sheets, the CMFC-reinforced BCTMP sheets had about5.2%,12.4%respectively higher in the bulk than that with the addition of cationic starch and beating treatment. It was further evidenced that CMFC could improve the strength of BCTMP interfiber bonding without significantly affect the bulk.Based on the above research, mechanisms behind strength-enhancing effects of MFC/CMFC were studied superficially, and the phenomena were explained with the structure of "angle brackets". Besides, the SEM, confocal images and mercury intrusion methods were applied to support this opinion.Finally, effects of CMFC on fines retention and flocculation of BCTMP were studied. It was found that addition of CMFC could significantly improve the fines retention of BCTMP regardless of the positive charge intensity of CMFC and the value of pH. Based on FBRM analysis, the flocculation of BCTMP with the CMFC was described as the50μm below-length fibers flocculating into the100μm above-length fibers. In addition, size of the flocculation was distribution in100～300μm range, and that could maintain uniformity of paper with the improvement of fines retention.