Principal component analysis as a tool to correlate properties of different laboratorial papers

We measured fibre morphological properties and corresponding handsheet paper properties in pulps obtained from Eucalyptus globulus, Acacia dealbata and Acacia melanoxylon wood samples. The three wood samples were chipped, cooked, and bleached according to standard procedures. The basic chip densities of the samples obtained from the three species studied were 0.351g/cm3, 0.387g/cm3 and 0.536g/cm3, respectively for A. dealbata, A. melanoxylon and E. globulus. All species were submitted to cooking with the following reaction conditions: active alkali charge = 22% (as NaOH); sulfidity index = 30%; liquor/wood ratio = 4/1; time to temperature = 90 min; time at temperature (160 ºC) = 120 min. Acacia species show higher pulp yield than the E. globulus sample used as a reference and cooking selectivity is higher in the Acacia species investigated. The three pulps were beaten in a PFI mill at 500, 2500 and 4500 revolutions under a refining intensity of 3.33 N/mm, and laboratory paper sheets were produced, including the unbeaten pulps, which made up 4 samples per species. The corresponding fibre characteristics in suspension were also determined. We used principal components analysis to investigate the differences in fibre characteristics and paper properties, as well as their interaction. Each value of these variables represents a mean of 10 tests, for the paper sheets. This methodology allowed us to determine how close, or how independent, the study variables were. We conclude there is a group of paper characteristics which depend strongly on each other - paper density, smoothness, tensile index, stretch, burst index, Schopper Riegler degree, internal cohesion and WRV – and are negatively correlated with the light scattering coefficient, opacity and brightness. On the other hand, intrinsic paper fibre resistance is strongly affected by fibre length and coarseness. On the basis of the properties we studied, it is clear that paper produced from Eucalyptus fibre has different properties from that produced from Acacia fibre. Papers produced from both species of Acacia are similar