121 WOOD RESEARCH 57 (1): 2012 121-130 USING NIR ANALYSIS FOR DETERMINATION OF HARDWOOD KRAFT PULP PROPERTIES Mária Fišerová, Juraj Gigac, Albert Russ, Marta Maholányiová Pulp and Paper Research Institute Bratislava, Slovak Republic (Received June 2011) ABSTRACT Multivariate data analysis and near-infrared region (NIR) spectroscopy was used to determine the physical and mechanical properties of unbleached and bleached hardwood kraft pulps with different chemical compositions and beaten to different levels. The differences between NIR spectra unbleached and bleached hardwood kraft pulps as well as between unbeaten and beaten pulps are very small. The calibration models developed for determination of pulp properties using NIR spectra analysis and conventional method had excellent predictive ability for tensile index (R=0.977-0.989), tear index (R=0.912-0.975) and stiffness (R=0.894-0.986). However, porosity does not show such good correlation (R=0.835-0.875) between measured and NIR predicted value. The correlation coefficients of calibration models made for combined unbleached and bleached pulps and separately for unbleached and bleached pulps were very similar. Average deviation between measured and NIR predicted properties of unknown hardwood kraft pulps confirmed the ability NIR analysis to determine hardwood kraft pulp properties. KEYWORDS: NIR spectroscopy, multivariate calibration, validation, hardwood kraft pulp, bleaching, tensile index, tear index, stiffness, porosity. INTRODUCTION Wood, pulp and final paper products are all materials of profound complexity and variability in both chemical composition and overall structure. The process of paper manufacture out of wood chips is a complex series of steps that include mechanical, physical and chemical alteration of the material. All of these procedures influence quality of the pulp and final paper product and often require complex and costly process control. However, measurements and evaluation of either pulp or paper requires not only an extensive financial spending for many specific instruments but also consumes substantial amount of time as many physical, chemical and optical analyses by means of conventional methods that may take up to several hours to complete. Application of infrared spectroscopy as an alternative approach allows for fast and reliable analysis by non-destructive means. Also, infrared spectroscopy requires much smaller samples than those