Preliminary studies on TCF bleaching of Pinus pinaster acetosolv pulps

Oxygen pre-treatment of Pinus pinaster acetosolv pulps has been studied as a first step towards TCF bleaching. Using a 23 factorial design, the influence of temperature (80–120 °C), time (1–2 h) and NaOH concentration (1.5–3%) on pulp yield in the oxygen stage, chemical composition and physical properties of the pulps obtained was studied. Pulps pre-bleached with oxygen in the conditions selected as optimal (80 °C, 1 h with 2.25% NaOH) have been bleached with TCF sequences which included stages with hydrogen peroxide or hydrogen peroxide–oxygen under pressure. Even if high degrees of delignification were reached, with a reduction in Kappa number up to 95% and without important loss of viscosity, the carbohydrates degradation, especially hemicelluloses in the acetic acid delignification, reduces the strength potential of the pulps.