Effects of Sodium chlorite delignification and alkaline extraction on bonding of CTMP fibres and the efficiency of dry strength additives

The strength properties of the long fibre fraction of mechanical pulp are limited by its low bondability. In this study the bonding ability of the long fibre fraction of CTMP is affected by chemical treatments (acid sodium chlorite delignification and alkaline extraction) and by dry strength additives. The chemical treatments mainly increase the fibre conformability (flexibility and collapsability). The acid sodium chlorite treatment also increases the specific bond strength. The dry strength additives increase the strength properties without affecting the sheet structure but the increase is small when the relative bonded area is small. The efficiency of the dry strength chemicals is higher when the conformability of the fibres is higher. The increase in the number of acidic groups with chlorite delignification did not affect fibre swelling much nor the ranking order of the different cationic starches