The influence of impulse drying on the performances of papers containing cationic starch and calcium carbonate.

Application: Calcium carbonate may eventually be a suitable filler for papers dried by impulse drying, but first there are some problems that will have to be solved.

The researchers evaluated the effect of impulse drying on the properties of paper sheets made with bleached kraft pulps from Eucalyptus globulus containing either 2% cationic starch or 15% Ca[CO.sub.3]. Additives-free samples and sheets with 2% cationic starch or 15% Ca[CO.sub.3] made from pulps beaten at 25[degrees]SR and 40[degrees]SR were prepared and impulse dried at six temperatures (25[degrees]C, 80[degrees]C, 150[degrees]C, 200[degrees]C, 25[degrees]C, and 350[degrees]C) using a laboratory-scale platen press. The basis weight of these papers was around 80 g/[m.sup.2].

Structural, mechanical, and optical tests were carried out. Impulse drying was found to increase the density of the paper sheet with cationic starch. Most of the paper strength properties are directly related to sheet density, so higher strengths were also achieved. Some problems of delamination and sticking were encountered. Delamination was more pronounced for papers with calcium carbonate than it was for additive-free papers or for papers with cationic starch. Impulse drying negatively affected most of the physical properties of paper containing the calcium carbonate. However, if these problems can be solved, introducing calcium carbonate could help compensate for the loss in opacity caused by impulse drying. S!

Mendes, Aguilar, Ranita, and Costa are with LEPAE, Dept. of Chemical Engineering, Faculty of Engineering, University of Porto, R. Roberto Frias 4200-465 Porto, Portugal. Belgacem is with Ecole Francaise de Papeterie et des Industrie Graphiques de Grenoble, INPG, BP: 65, 38402 St Martin d'Heres, France. Silvy is with the University of Beira Interior, Dept. of Paper Science and Technology, P-6200 Covilha, Portugal. Email Belgacem at [e-mail].