Recebido em 25/5/08; aceito em 26/1/09; publicado na web em 3/7/09 ESTIMATION OF PHYSICAL PROPERTIES OF KRAFT PAPER BY NEAR INFRARED SPECTROSCOPY AN PARTIAL LEAST SQUARES REGRESSION. The main objective of the present work is represented by the characterization of the physical properties of industrial kraft paper (i.e. transversal and longitudinal tear resistance, transversal traction resistance, bursting or crack resistance, longitudinal and transversal compression resistance (SCT (Compressive Strength Tester) and compression resistance (RCT-Ring Crush Test)) by near infrared spectroscopy associated to partial least squares regression. Several multivariate models were developed, many of them with high prevision capacity. In general, low prevision errors were observed and regression coefficients that are comparable with those provided by conventional standard methodologies.Keywords: kraft paper; multivariate calibration; near infrared spectroscopy. INTRODUÇÃONo Brasil, a madeira para celulose e papel provém de várias espé-cies arbóreas de eucalipto e pinus, destacando-se Eucalyptus grandis, Eucalyptus saligna, Eucalyptus urophyla, outras em menor escala. As de pinus correspondem a Pinus elliottii, Pinus taeda e Pinus caribea.O processo de obtenção de polpa de madeira antecede a produção de papel, sendo genericamente definido como polpação. O processo envolve a separação das fibras da madeira mediante a utilização de energia mecânica, térmica ou química ou a combinação das três. O processo químico tem como objetivo a dissolução da lignina, preservando a maior parte da celulose e hemicelulose.A polpa kraft (palavra alemã que significa forte) origina papéis de maior resistência e coloração escura.1 De acordo com o mesmo autor, as principais variáveis que afetam o processo de polpação kraft estão relacionadas com as características dos cavacos de madeira (espécie, qualidade, umidade, densidade), do licor de cozimento (concentração de álcali ativo), do controle da polpação (relação licor:madeira, temperatura, pressão, curva tempo/temperatura (fator H)), além de outros parâmetros como grau de deslignificação desejado (indicado pelo número kappa) e álcali residual. De maneira geral, as empresas buscam uma variação mínina no processo e na qualidade da polpa, controlando rigorosamente as variáveis de polpação. Desta maneira, consegue-se um produto uniforme, com qualidade compatível com as especificações finais, delimitadas pelos testes de resistência do papel.Antes da polpa ser encaminhada à máquina de papel passa por um processo chamado de refinação, em que as fibras são submetidas à ação mecânica, tendo como consequência penetração de água na parede celular, ruptura de algumas ligações de hidrogênio entre fibras e fibrilação da parede primária, o que contribui com o aumento da flexibilidade das fibras e melhora do entrelaçamento. 1,2Um aumento no processo de refinação provoca decréscimo da resistência ao rasgo, devido ao aumento do número de cortes nas fibras, e aumento da resistência ao arrebentamento e à tração, conse...

Eucalyptus dunii has been commercially used in southern Brazil because of its relatively good frost tolerance and adequate productivity in the winter months. More recently, interest has grown in cultivating Eucalyptus benthamii Maiden & Cambage, which presents even superior frost tolerance compared to E. dunii and is highly productive as well. The quality of E. benthamii for pulp production is not yet proven. Thus, the chemical, anatomical, and technological aspects of pulp made from E. benthamii were compared with those of E. dunii for unbleached paper production. Samples of E. benthamii chips were obtained and analyzed for their basic density, chemical composition, higher heating value, trace elemental analysis, and chip size distribution. The chips were kraft cooked using conditions that produced a 74 ± 6 kappa number. The pulps were characterized for kappa number, yield, viscosity, and morphologic characteristics (e.g., length, wall thickness, and coarseness). Black liquor was analyzed for total solids, organics, inorganics, sodium sulfide, sodium hydroxide, and sodium carbonate. Brownstocks were beaten at five different energy levels in a Valley beater, and the physical strength properties of 120 g/m² handsheets were measured to develop a beater curve. The results of this study showed differences in delignification between the two woods and lower pulp yield for E. benthamii , which are related to their chemical compositions and basic densities. The E. benthamii studied in this work exhibited higher amounts of lignin and extractives, lower carbohydrate content, and lower basic density. However, cooking a blend of the two woods afforded good results in pulping and in physical pulp properties.

Variability in wood properties has a major impact on pulp quality and the cost associated with pulp production. Frequently, accounting data for green tons of wood across the mill scales and the tons of pulp produced suggest that the pulp mill has affected the pulp yield because the tons of purchased wood divided by the tons of pulp produced changes. The current work examines the impact of the time — from when a tree is harvested in the forest to the time it is brought across the scales at the mill — on accounting yield and operating cost. Percentage weight loss (assumed to be changes in moisture content) were determined for Pinus taeda, Eucalyptus dunni, and Eucalyptus grandis over a 12-week period in the winter and summer seasons. Wood samples were obtained immediately after being harvested. The percentage weight loss within the first 5 days of storage varied from 2% to 13%, depending upon species and season, and reached 36% after 11 weeks of storage. For a 1000 tons/day mill with a 55% pulping yield on o.d. fiber, the difference between using fresh-cut wood verses cut trees that have been stored for 11 weeks is 1130 green tons. Assuming the mill pays $45/green ton, the change in green log usage between fresh-cut and 11-week-old logs can cost the mill US$50,850 per day.