CHEMIMECHANICAL PULPING OF EUCALYPTUS-GRANDIS

Eucayptus is currently one of the main fibrous raw materials used in the pulp and paper industry in given parts of the world. The objective of the present paper is to optimize the chemimechanical pulping conditions for Eucalyptus grandis, evaluate the pulp quality obtained, and draw 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, the chemical stage was carried out in a stainless steel digester with a liquor recirculation system. The mechanical stage was carried out in an 8-in. atmospheric disk refiner. Sodium sulfite and sodium hydroxide were added as chemical reactives. The central composite experimental design used involved five levels for the two variables studied (2(2) factoral design + star + central point). Three repetitions of the central point were carried out to check for errors. The variables studied were: 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 temperature and time at maximum temperature were, respectively, 20 and 90 minutes. A constant level of sodium hydroxide was maintained in all the experiments (1.5% oven-dry wood). Pulp evaluation was carried out using the usual characterization techniques. Chemical and physical evaluations, including optical testing, were, for the most part, done in accordance 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 the variables studied for the chemimechanical pulping of Eucalyptus grandis. The pulps obtained could be used as furnish in printing and writing paper grades. The positive correlation between sulfonate concentration and water retention value (WRV) suggests that by increasing fiber wall swelling, the number of sites accessible to sulfonation is increased. The tensile index correlates positively with the degree of sulfonation and with the water retention value of the pulps. It decreases according to the fraction retained in a 30-mesh screen (due to the presence of numerous shives) and increases according to the fraction of fines passing through a 270-mesh screen.