THE ROLE OF LIGNIN IN THE MECHANICAL PERMANENCE OF PAPER .2. EFFECT OF ACID GROUPS

The effect of sulphonic acid groups on the mechanical permanence of pa per was studied by accelerated aging of thermomechanical pulp (TMP) th at was sulphonated to different levels. Results showed that acid group s in the hydrogen form have a significant negative effect on the mecha nical permanence of paper. However, neutralization of these groups by treatment with sodium hydroxide or calcium carbonate significantly imp roved the mechanical permanence of paper. Sulphonated mechanical pulp after washing with tap water has good mechanical permanence because th e acid groups are mostly in the calcium form due to the ion exchange d uring washing.