INTERACTIONS OF CATIONIC POLYMERS WITH COMPONENTS IN THERMOMECHANICALPULP SUSPENSIONS

The interactions of three cationic polymers with components in suspens ions of unbleached and peroxide bleached TMP, and their isolated disso lved and colloidal substances in water, were studied. The polymers dif fered in their molecular mass, charge density, and degree of branching . The optimum polymer dose (OPD), which gives the most effective desta bilization of colloidal turbidity-causing substances, differed with th e type of polymer added. The OPD was also influenced by alkaline perox ide bleaching of the TMP, and by removal of the fibers and fines prior to polymer addition. Lipophilic wood extractives, anionic hemicellulo ses, and UV-absorbing substances formed aggregates with the polymers. These aggregates could be sedimented by centrifugation. For unbleached TMP, only small differences in the OPD values were found upon additio n of the different polymers to fines-and fiber-free water samples. How ever, when fines and fibers were present, the OPD values were higher a nd differed considerably with the polymer type. For peroxide bleached TMP, larger amounts of the polymers were needed to reach the OPD compa red to unbleached samples. This was probably due to aggregation of the cationic polymers with anionic hemicelluloses, primarily polygalactur onic acids, known to be released into the water phase in alkaline pero xide bleaching. Enzymatic degradation of the polygalacturonic acids lo wered the OPD values. The results demonstrate that there are significa nt differences in the interactions of different cationic polymers with the components in mechanical pulp suspensions. Such information can l ead to better control of colloidal stability in papermaking.