Rosin sizing of pulps modified by TEMPO-mediated oxidation

TEMPO-mediated oxidation was applied to a bleached kraft pulp to prepare oxidized pulps with carboxyl content of 0.06-0.45 meq./g. Then, handsheets were prepared from the oxidized pulps and sized with aluminum sulfate and rosin emulsion size at pH 4.5. The sizing was studied in terms of carboxyl content of the pulp and retention values of aluminum and rosin size. The results showed that sizing performance of the handsheets prepared from the oxidized pulps was clearly improved in most cases examined. However, the retention values of rosin size of the handsheets decreased to some extent with increased carboxyl contents of the oxidized pulps. Electron scanning microscopic observation of the handsheet surfaces revealed that the rosin size emulsion particles on the pulp fibers were more evenly distributed by using the oxidized pulps. Aluminum components were adsorbed on the pulp fibers in a different way compared with the reference pulp, even though retention values of aluminum were roughly equal. In consequence, this difference in adsorption behavior of aluminum components brought about a different distribution of rosin size components. The introduction of carboxyl groups into pulp fibers by the TEMPO-mediated oxidation greatly influenced the retention behavior of wet-end additives and the resultant sizing behavior.