Upgrading OCC and Recycled Liner Pulps by Medium-consistency Ozone Treatment

Abstract

Possibilities for improving the properties of old corrugated container (OCC) pulp by applying low levels of ozone at medium consistency were evaluated. In addition, pulps obtained from kraft liner and corrugating medium were considered. Ozone reduces the kappa number but the surface charge of the fiber is not changed. Ozonation clearly increases the relative bonded area (RBA) in sheets made from treated fibers. It was shown that RBA is essential for Concora medium test (CMT) resistance. Papermaking properties like tensile strength, internal bond strength, compression strength and CMT were significantly increased even at the lowest ozone charge employed. For OCC pulp, it is shown that similar improvements can be reached by refining and alkali treatment. Nevertheless, alkali has a greater effect on pulp freeness and produces a higher charge in the application. Properties like internal bond strength, compression strength and CMT of a recycled unbleached pulp can be notably increased by the application of low level of ozone.