Title
Influence of pulp suspension pH on the performance of chitosan as a strength agent for hardwood CMP paper
Authors
MOSTAFA ROHI OMID RAMEZANI MEHDI RAHMANINIA SEYED MAJID ZABIHZADEH and MARTIN A. HUBBE

Received January 4, 2015
Published Volume 50 Issue 7-8 July-August
Keywords chitosan, dry strength, chemi-mechanical pulp, fiber, wet end, pH

Abstract
Chitosan – a well-known carbohydrate – has found new applications in the papermaking industry. Although the effect of pH on the properties of chemical pulps has been investigated in a number of studies, it has not been reported related to hardwood mechanical pulp, to our knowledge. In the present research, the effect of different pH levels (5.5, 7 and 8.5) on the performance of chitosan as a dry strength additive in paper produced from chemi-mechanical hardwood pulp was studied. The results indicated that the effect of chitosan on the properties of chemi-mechanical paper depended strongly on the pH of the furnish. The addition of chitosan to the stock at acidic pH did not have any specific effect on the strength properties. In contrast, neutral and alkaline pH resulted in improvements in the dry strength properties of paper sheets. The maximum apparent density was observed at pH 8.5, which was attributed to the precipitation of the chitosan on the fiber surface. The results showed that chitosan would be more effective in low dosages. The dependence of chitosan performance on pH in chemi-mechanical pulp was similar to that reported for chemical pulps.