Impulse drying effect on some properties of paper made from hardwood and softwood Portuguese pulps

The influence of impulse drying on paper properties was investigated using hand sheet papers made from bleached kraft Eucalyptus globulus and unbleached kraft Pinus pinaster. Two basis weights (60 and 80 g/m(2)) and two refining degrees (25 and 40degreesSR) were tested. The paper samples were pressed at six temperatures, namely: 25, 80, 150, 200, 250 and 350degreesC. The impulse drying technique was found to have more pronounced beneficial effects on papers made from Eucalyptus globulus pulp to compare with that observed in the case of paper made from Pinus pinaster pulp. In fact, it was found that impulse drying produced an excellent densification of fibrous mat and consequently higher strengths were reached. However, some delamination on the surface of the paper for sheets having higher basis weight and refining degree were detected. Paper samples from Eucalyptus globulus pulp presented better smoothness. The use of 350degreesC pressing temperature in Eucalyptus globulus pulp induced a decrease in the brightness of this set of paper samples. There were no major effects in most physical properties for paper made from Pinus pinaster pulp. This furnish was found to exhibit more problems of delamination even for the lowest basis weight and refining degree. Thus, image analysis of the paper cross-sections and visual examination was carried out in order to ascertain the delamination on the paper sheets occurring when paper was pressed at high temperatures.