Effect of Pulping Conditions on the Bleachability of Hardwoods, 1995 Pulping Conference Proceedings

Krishna R Kumar, Hou-min Chang, Hasan Jameel

North Carolina State University

As environmental pressures increase, extended delignification systems are finding widespread applications in the pulp & paper industry. The number of variables influencing the operation of extended delignification cooking systems are more than that of conventional kraft process. Optimization of these variables is critical in maintaining both brownstock and bleached pulp quality. The objective of this research was to study the effect of pulping conditions on the bleachability of mixed North American Hardwoods cooked by the Rapid Displacement Heating (RDH) Process. A 2 3 factorial design was used to study the effect of varying Active Alkali(AA), H-Factor & Temperature in the White Liquor stage, on bleachability. The bleaching sequences studied included (D50+C50)(E+O)D and D(E+O)D. At 100% substitution in the DC stage, high AA and low H-Factor gave a higher final brightness. The effect of AA was less pronounced if the substitution is lowered to 50%. The effect of varying the alkalinity in the Warm Fill & Hot Fill Stages was also studied. Addition of White Liquor in the two pre treatment stages increased the final pulp brightness significantly. The improvement in bleachability could be due to more efficient removal of dissolved organics (extractives & lignin) or due to changes in the characteristics of the residual lignin At the same kappa number the extended delignified pulps gave a higher final brightness when compared to conventional kraft pulps.