Influence of the operating conditions in the acetone pulping of wheat straw on the properties of the resulting paper sheets

Abstract

A central composite factor design was used to examine the influence of independent variables in the acetone pulping of wheat straw (processing temperature, time, and acetone concentration) on the yield of the resulting pulp, and on various physical properties of paper sheets (breaking length, stretch, burst index, tear index and brightness) obtained from it. Equations that related each dependent variable to the different independent variables were obtained, and these reproduced the experimental results for the yield, breaking, stretch, burst index and brightness obtained at temperatures, times, and acetone concentrations over the ranges 140–180°C, 60–120 min and 40–80%, respectively, with errors less than 20%. Obtaining the optimum breaking length, stretch, burst index and tear index for the paper sheets (3456 m, 1.42%, 1.36 kN/g and 3.86 mNm 2/g, respectively) entails using a high temperature; the processing time and acetone concentration only influence stretch, optimization of which requires using a short time and a low concentration. The optimum brightness (30.44%) is achieved with a low temperature, a short time and a medium acetone concentration. In order to minimize losses of solvent during its recovery and recycling while ensuring acceptable levels of the properties of the paper sheets, a high temperature, a low acetone concentration and a short time can be used; the brightness level thus obtained is only 10% lower than the optimum value.