TCF bleaching of hardwood pulps obtained in organic acid media:: Production of viscose-grade pulps

High-purity, viscose-grade pulps have been produced by means of delignification (in media containing formic or acetic acid) and TCF bleaching (using a E(O)ZP sequence). Aspen or Eucalyptus globuluswood chips were treated in media made up of either acetic acid, water and HCl or formic acid, water and hydrogen peroxide (Acetosolv and Milox technologies). Under selected conditions, unbleached pulps with kappa numbers in the range 14.0-28.5 were obtained at 50.0-53.7% pulp yield. These samples were subjected to E(O)ZP bleaching to reach the viscose-grade target values for chemical and physicochemical properties. Among the pulps tested, the bleached Milox pulp from Eucalyptus wood showed the best properties to be used for viscose manufacture (pentosan content of 1.4%, SCAN viscosity of 598 mL/g, ISO brightness of 89.9% and alkaline resistances of 90.1% and 97.0% in the R-10 and R-18 tests).