Cationic starch as a dry strength additive for bleached Eucalyptus globulus kraft pulps

Paper sheets, filled with calcium carbonate, and made with bleached Eucalyptus globulus kraft pulps (refined to 40 degrees SR, similar to 270 CSF) were prepared in the presence of several cationic starches (CS), as dry strength additives. Six cationic starches having different degrees of substitution (DS), namely: 0.017, 0.022, 0.034, 0.047, 0.06 and 0.09 and 3 levels of addition, i.e. 0.5, 1 and 2% CS with respect to oven dried pulp, were used. It was found that internal cohesion strength and burst index were the parameters most sensitive to the presence of CS, increasing by up to 80 and 50%, respectively, for paper made with 2% CS having a DS of 0.034. Cationic starches with DSs of 0.047 and 0.06 also gave very good results. As expected, filler decreased the overall mechanical properties, i.e. tensile and burst indexes, internal cohesion strength and elongation. The use of CS with a DS equal to 0.034 compensated for the decrease in paper properties induced by the use of calcium carbonate filler.