Rosin sizing of pulps modified by TEMPO-mediated oxidation

TEMPO-mediated oxidation was applied to a bleached kraft pulp to prepare ox idized pulps with carboxyl content of 0.06-0.45 meq./g. Then, handsheets we re prepared from the oxidized pulps and sized with aluminum sulfate and ros in emulsion size at pH 4.5. The sizing was studied in terms of carboxyl con tent of the pulp and retention values of aluminum and rosin size. The resul ts showed that sizing performance of the handsheets prepared from the oxidi zed pulps was clearly improved in most cases examined. However, the retenti on values of rosin size of the handsheets decreased to some extent with inc reased carboxyl contents of the oxidized pulps. Electron scanning microscop ic observation of the handsheet surfaces revealed that the rosin size emuls ion particles on the pulp fibers were more evenly distributed by using the oxidized pulps. Aluminum components were adsorbed on the pulp fibers in a d ifferent way compared with the reference pulp, even though retention values of aluminum were roughly equal. In consequence, this difference in adsorpt ion behavior of aluminum components brought about a different distribution of rosin size components. The introduction of carboxyl groups into pulp fib ers by the TEMPO-mediated oxidation greatly influenced the retention behavi or of wet-end additives and the resultant sizing behavior.