Simplified modification of bleached softwood pulp with carboxymethyl cellulose

An ECF-bleached softwood pulp was treated with carboxymethyl cellulose (CMC). The CMC sorptions were carried out under specified conditions (60 degrees C, pH 12.5, CMC addition 1%, pulp consistency 5%) in order to introduce more charged groups on the surface of fibres. The beating of pulp, pH-value, degree of substitution (DS) of CMC and electrolyte concentration had a major impact on the amount of CMC attached. The increase in the water retention values (WRV) of the CMC-treated pulps was very significant, and was associated with improved internal (approximately 50% increase) and tensile strengths of resultant handsheets. These handsheets prepared in water and in electrolyte solution were further studied by electron microscopy (ESEM). As the sorption conditions used are similar to those in papermaking systems, this surface modification method may be advantageous in practice, for example, after the refining stage.