Influence of Degree of Substitution of Carboxymethyl Cellulose on Wet Strength of Pulp Handsheets Prepared by Dual Polymer System

Carboxymethyl cellulose (CMC)-containing pulp handsheets were prepared by internal additions of a cationic polymer (CP) and CMCs with various degrees of substitution (DS) ranging from 0.49 to 1.29 to pulp slurries. The influence of the DS of CMC on dry- and wet-tensile strengths of the CMC-containing handsheets was studied. CMC contents in the handsheets were controlled to be almost equal for all the handsheets by controlling the CP addition level. Almost no influence of the DS values of CMCs ranging from 0.63 to 1.29 on the highest dry-tensile strengths was observed for the handsheets, when CMC contents in the handsheets were almost equal. Wet-tensile strengths of the handsheets soaked in solutions consisting of ethanol, water and calcium chloride with various weight ratios similarly decreased for all CMC-containing handsheets with increasing water content of the soaking solutions, irrespective of the DS of CMCs. However, wet-tensile strength of the handsheets increased with increasing the DS of CMC, when ethanol content of the soaking solutions was approximately 20%. The obtained results indicate that the amount of CMC-COO-Ca2+Cl- structures formed between CMC and CaCl2 in the handsheets during the soaking treatment primarily contributes to the wet-strength development.