Effect of partially substituting MgO for NaOH on bleaching of pine (Pinus massoniana) thermomechanical pulp

Bleached thermomechanical pulp (TMP) has been applied in the production of newsprint and supercalendered (SC) paper or other paper products. Recent studies on the alkaline peroxide bleaching with magnesium-based alkalis indicated that the bulk and optical properties can be improved, and effluent load can be reduced. In this work, MgO was partially used in alkaline peroxide bleaching process of pine (Pinus massoniana) TMP to investigate the effect of MgO substitution for NaOH on the pulp properties and effluent characteristics. The present research showed that partial substitution of MgO for NaOH could decrease the dissolution of chemical components in pulp fibers, thus, improving the pulp yield and decreasing the effluent load. When the substitution percentage of MgO for NaOH increased from 0% to 50% at 3.5% alkali charge, the bulk of the bleached pine TMP increased from 3.45 cm3/g to 3.69 cm3/g, while the opacity was improved from 84.7% to 89.1%, the cationic demand and CODCr of the effluent decreased by 31% and 22%, respectively. However, the MgO substitution had decreased the brightness and tensile index of the bleached TMP.