Influence of process variables in the soda-anthraquinone pulping of sunflower stalks on the properties of the resulting paper

This paper discusses the influence of independent variables in the pulping of sunflower stalks [viz. temperature (125-175 degreesC), cooking time (30-90 min), soda concentration (5-15%), anthraquinone concentration (0-0,1%) and liquid/solid ratio (4:1-8:1)] on pulp yield and on the breaking length, stretch, burst index and tear index of the resulting paper sheets. By using a central composite factor design, equations relating each dependent variable to the different independent variables were obtained that reproduced the experimental results for the dependent variables with errors less than 20%. Ensuring optimal pulp yield (68.7%), and also optimal burst index (1.52 kN/g) and tear index (5.1 mNm(2)/g), for the papers sheets entails using a temperature of 125 degreesC, a cooking time of 30 min, a soda concentration of 5%, a liquid/solid ratio of 8:1 and no anthraquinone. The optimum values for the breaking length (3066 m) and stretch (1.45%) are obtained by using a temperature of 175 degreesC and an anthraquinone concentration of 0.01%, in addition to high values of the soda concentration and time (15% and 90 min, respectively) for the stretch and low ones (5% and 30 min, respectively) for the breaking length. Using low values of all the independent variables provides values for the dependent variables that differ little from their optimum levels (by 2.6%,9.9%,16.6%,11.8% and 7.5% for pulp yield, breaking length, stretch, burst index and tear index, respectively) while resulting in substantial savings of chemicals, heating energy and immobilized capital as the process can be implemented on a smaller scale.