Paper properties and swelling properties of ozone-based ECF bleached softwood kraft pulps.

Application:This study shows that ozone and hydrogen peroxide can be used with advantage in (DZ) and (PO) bleaching stages in an ECF "light" bleaching process.

This study compares the physical properties of DEoQ(PO), (DZ)Eo[D.sub.1] E[D.sub.2], and (DZ)EoQ(PO) bleached oxygen delignified softwood kraft pulps to the same properties of a DEo[D.sub.1]E[D.sub.2] bleached ECF reference pulp. Both (DZ)Eo prebleaching and pressurized peroxide final bleaching reduced the AOX formation considerably, although the Q(PO) final bleaching also increased the COD effluent load. The tear strength was maintained, but the (DZ)Eo prebleaching had a slight negative effect on fiber strength as indicated by lower wet zero span strength of beaten (DZ)Eo[D.sub.1]E[D.sub.2] and (DZ)EoQ(PO) bleached pulps. Pressurized peroxide final bleaching yielded pulps with higher fiber charge than chlorine dioxide final bleaching. Compared to the [D.sub.1]E[D.sub.2] final bleached pulps, the increased number of charged groups in DEoQ(PO) and (DZ)EoQ(PO) bleached pulps seemed to promote increased fiber swelling of both unbeaten and highly beaten pulps. The more swollen unbeaten Q(PO) final bleached pulps formed denser paper sheets with higher tensile strength and wet zero span strength. A highly charged and swollen pulp seems to be advantageous with respect to beatability when the pulp is beaten to a target tensile strength.

Toven is a research scientist at the Norwegian Pulp and Paper Research Institute, Trondheim, Norway. Email Toven at [e-mail].