Acetone Pulping of Wheat Straw. Influence of the Cooking and Beating Conditions on the Resulting Paper Sheets

Abstract

This paper reports on the influence of independent variables in the pulping of wheat straw [viz., cooking temperature (140−180 °C), time (60−120 min), and acetone concentration (40−80%)] and of the number of PFI beating revolutions (0−1750) to which the pulp is subjected, on the yield and Shopper−Riegler index of the pulp, and on the breaking length, stretch, burst index, and tear index of the resulting paper sheets. By using a central composite factorial design, equations that relate each dependent variable to the different independent variables were obtained that reproduced the experimental results for the dependent variables with errors of less than 25%. Ensuring the optimal Shopper−Riegler index for the pulp (29.53 °SR), and also the optimal stretch (2.37%) and burst index (2.63 kN/g) for the paper sheets, entails using a 180 °C temperature and 1750 number of PFI beating revolutions. The use of these conditions in conjunction with a 40% acetone concentration and a 60 min cooking time allows one to save solvent in the recovering and recycling steps and also to increase production. The values thus obtained for the breaking length and tear index differ by less than 12% and 29% from their optimum levels (5781 and 4.72 mN·m2/g, respectively).