BLEACHED CHEMICAL PULP FROM EUCALYPTUS-GRANDIS WOOD PRODUCED BY PEROXYFORMIC ACID PULPING AND PHOTOCHEMICAL BLEACHING

Good quality Totally Chlorine Free bleached chemical pulp was produced from Eucalyptus grandis wood chips under mild conditions. The process used a combination of peroxyformic/formic acid pulping in three stage s (HCOOOH (3 h, 75 degrees C), HCOOH (110 degrees C, 2 h) and HCOOOH ( 3 h, 75 degrees C)) and a photochemical bleaching in basic medium at 8 5 degrees C in three stages: ground state oxygen treatment (Ih) follow ed respectively by action (Ih) of singlet oxygen generated by methylen e blue (5 x 10(-5) moll(-1)) and hydrogen peroxide (2 %, 1 h). The UV- visible irradiations (wavelengths > 300 nm) involved a non-prohibitive equipment such as Pyrex vessel and high pressure mercury lamps. Mild alkaline extraction of the dissolved material from the spent liquors a llowed the recovery in large quantities (57 %) of phenolic lignin with out carbohydrates due to a selective cleavage of the phenolic formate entities. The lignin fractions were analyzed by size exclusion chromat ography, IR and H-1 NMR spectrometries. Under the conditions used, the photochemical delignification was very efficient (unbleached pulp: Ka ppa Number (KN)=7.0; photochemically bleached KN < 0.5; thermally blea ched KN = 1.7) and the brightening effect strong (unbleached pulp: Bri ghtness index (BI)= 61.1; photochemically bleached BI = 89.6; thermall y bleached BI = 83.8). The bleaching sequence used induced some depoly merization of the cellulose which is more pronounced for the photochem ical process. (Intrinsec viscosity of unbleached pulp: [eta] = 1145 dm (3) kg(-1) photochemically bleached [eta] = 670 dm(3) kg-l and thermal ly bleached [eta] = 837 dm(3) kg(-1)).