Study On The Effect Of Substituting Magnesium-Base For Sodium-Base On The Peroxide Thermomechanical Pulp

Thermomechanical pulp (TMP) or bleached thermomechanical pulp (BTMP), as one of the main high-yield pulps (HYPs), has been applied in the production of newsprint, supercalendered (SC) paper and other paper or paperboard products owing to its excellent bulk, opacity and strength properties. Usually, the proportion of BTMP in newsprint is about15%～20%interiorly and about80%overseas. The proportion of BTMP in SC paper is about60%～70%interiorly.Recently, studies on the peroxide bleaching of HYPs showed that a higher opacity and bulk and a lower effluent load were obtained from the magnesium-based process than from the sodium-based process.The present study results showed that the pH value, cationic demand, CODCr, and conductivity of the effluent decreased notablely, with the increase of substitution percentage of MgO for NaOH. The dissolution of benzene alcohol extractives, Klason lignin, and holocellulose of the pulp fibers decreased. Meanwhile, the bulk, opacity, and light-scattering coefficient increased, as well as the bleaching yield. However, the addition of MgO had decreased the brightness and strength properties of the resultant pulp. In addition, the effluent load and the dissolution of pulp chemical components at4.0%alkali charge were higher than those at3.5%alkali charge, respectively, but resulted in a lower bulk compared to that at3.5%alkali charge.The cationic demand, CODCr, and conductivity of the effluent decreased by31%,22%, and29%, respectively, when the substitution percentage of MgO for NaOH increased from0%to50%at3.5%alkali charge, meanwhile, the opacity and bulk of pine (Pinus massoniand) increased from84.69%and3.45cm3/g to89.09%and3.70cm3/g, increased by5.2%and7.2%, respectively. The brightness and tensile index decreased by8.7%and19.0%, but still kept a brightness of59.42%ISO and a tensile index of18.89N-m/g, respectively.The additon of MgO in the hydrogen peroxide bleachig process can improve the opacity and bulk of pine BTMP, which would bring the enterprise a considerable benefit once applied in the production.