STUDIES ON PITCH TROUBLE CONTROL OF SULFITE PULP WITH SURFACTANTS

Effects of additives on the deresination and the pulp yield were evaluated on the same pulping degree level during sulfite cooking of softwood chip. The additives included hydrotropic agents and mixtures of surfactant with hydrotropic agent.By the addition of sodium xylene sulfonate (I) in an amount of 0.25%, based on dry wood, the reduction in resin content and the yield of unbleached pulp were greater by amounts of 18% and 2.3%, respectively, in comparison with the results from a control cooking. About the same effects could be obtained with sodium tetralin sulfonate or sodium methylnaphthalene sulfonate, but the deresination effect decreased in such cases under the addition of higher amounts.When mixtures of (I) with sodium dodecylbenzene sulfonate (II) or mixtures of (I) with polyoxyethylene lauryl ether (n=7) (III) were added, the yield of unbleached pulp increased, but no deresination effect was observed. A ternary surfactant mixture comprising (I), (II) and (III) in the mixing ratio of 1:1:2 showed excellent results when added in amounts of 0.05 to 0.25%, as indicated in the reduction in resin content of 14.7 to 21.5% and in the increase in yield of 0.7 to 2.0%, in comparison with those from a control cooking.There was no correlation between the resin content of refined pulp obtained by the treatment in six stages and that of unbleached pulp, and there seemed to be a slight trend towards increasement in resin content in the case of refined pulp from unbleached stock cooked with additives. But the resin contents of refined pulp were well below the maximum allowable for dissolving pulp in nearly all cases.