The effects of CMC attachment onto industrial and laboratory-cooked pulps

The effect of surface carboxymethylation of industrial and laboratory-cooked pulp was studied regarding attached amount, fibre properties and paper sheet strength. The strength development was compared with the effects of PFI beating. Attachment of CMC was shown to be equally effective with industrial pulp as with laboratory-produced pulp. The attachment level was 100% for both pulp types and no difference in paper strength enhancement could be detected. CMC attachment had a small impact on sheet density, especially compared to PFI beating. Moreover, surface carboxymethylation was shown to increase the shape factor, reduce the number of kinks per fibre and to increase the rewetted zero-span index. This straightening effect of CMC was interpreted in terms of an increase in carboxyl group repulsion on the fibre surface and is probably a factor contributing to the increase in paper strength. Differences in fibre curl between industrial and laboratory-cooked pulp decreased when CMC was attached to the fibre surface. This may explain why no differences in CMC efficiency could be detected.