Strength improvement and energy savings for HT-CTMP through chemical treatments of pulp fractions

This work studied how the properties of a high yield pulp can be improved by chemical treatments performed separately on fines and long fibres of mechanical pulp. The fines were separated from a softwood HT-CTMP (high temperature chemi-thermomechanical pulp) using a 48 mesh screen. The amount of the fines or accept was 18% of the pulp. The bonding ability of the fines was enhanced by two different chemical treatments: by partial delignification of the fibre surfaces using ozone (O3) re-sulting in increased number of functional groups, and by partial delignification of the fibres using alkaline hydrogen peroxide (AHP), therefore increasing the conformability of fibres and thus also the bonding between the fibres. The bonding ability of the long fibres or reject was enhanced by chemical treatment using AHP. The tensile index of the accept was improved up to 70% with minimal bulk loss. The recombined pulp strength properties were improved up to 35% at given CSF freeness. By treating the reject with AHP, strength was improved at given sheet air re-sistance (indicating porosity) more than with the AHP treatment of accept. Savings in refining energy were 50% at the tensile strength of 40 Nm/g compared to the refer-ence HT-CTMP case.