Investigation on the Influence of Pulping Conditions on Delignification and Viscosity of Soda Pulp from Bagasse

The influence of pulping temperature, time and alkali charge on residual lignin and viscosity of soda pulp produced from bagasse was investigated. Two pulping temperatures (175 ^oC and 185 ^oC), three pulping times (20, 30 and 40 minutes) and three alkali charges (14, 16, 18% NaOH, OD basis) were used. Factorial experiment based on randomized block design was applied to analyze the effect of pulping variables on total yield, accepted yield, pentosans content, viscosity and kappa number of the pulps. The results showed that higher intensity of pulping reduced both total yield and kappa number. At 175 ^oC pulping temperature, increasing pulping time and alkali charge reduced pentosans content and viscosity, but the reduction of these properties was severe at pulping temperature of 185 ^oC. Higher pulping temperature and time reduced pH of black liquor, which indicates consumption of more alkali during pulping. At milder condition of pulping higher pulp viscosity and pentosans were measured and at severe pulping condition, both properties were reduced which indicates the degradation of carbohydrates especially cellulose. The measured viscosity of pulps produced at 175 ^oC and 185 ^oC were 11.73 and 11.34 cps, respectively, and the related values for pulps produced at 20, 30 and 40 minutes pulping time were respectively 11.78, 11.57 and 11.24 cps. The results showed that pulping time and temperature are the most influential factors on carbohydrate degradation and the influence of alkali charge is not as severe as pulping time and temperature.