CHEMIMECHANICAL PULPING OF EUCALYPTUS-GRANDIS

Eucayptus is currently one of the main fibrous raw materials used in t he pulp and paper industry in given parts of the world. The objective of the present paper is to optimize the chemimechanical pulping condit ions for Eucalyptus grandis, evaluate the pulp quality obtained, and d raw conclusions regarding its potential use. The raw material used was Eucalyptus grandis industrial chips obtained at a Celulosa Argentina mill in Puerto Piray, Misiones, Argentina. For all the experiments, th e chemical stage was carried out in a stainless steel digester with a liquor recirculation system. The mechanical stage was carried out in a n 8-in. atmospheric disk refiner. Sodium sulfite and sodium hydroxide were added as chemical reactives. The central composite experimental d esign used involved five levels for the two variables studied (2(2) fa ctoral design + star + central point). Three repetitions of the centra l point were carried out to check for errors. The variables studied we re: initial amount of sodium sulfite in the wood(0.9 to 3.5% oven-dry- wood) and reaction temperature (96 to 124 C). Times until maximum temp erature and time at maximum temperature were, respectively, 20 and 90 minutes. A constant level of sodium hydroxide was maintained in all th e experiments (1.5% oven-dry wood). Pulp evaluation was carried out us ing the usual characterization techniques. Chemical and physical evalu ations, including optical testing, were, for the most part, done in ac cordance with TAPPI procedures. The results obtained indicate that the central point of the design used in our research (110 C and 2.5% oven -dry wood sulfite), appears to represent the optimal conditions for th e variables studied for the chemimechanical pulping of Eucalyptus gran dis. The pulps obtained could be used as furnish in printing and writi ng paper grades. The positive correlation between sulfonate concentrat ion and water retention value (WRV) suggests that by increasing fiber wall swelling, the number of sites accessible to sulfonation is increa sed. The tensile index correlates positively with the degree of sulfon ation and with the water retention value of the pulps. It decreases ac cording to the fraction retained in a 30-mesh screen (due to the prese nce of numerous shives) and increases according to the fraction of fin es passing through a 270-mesh screen.