Effect of Depithing on Bagasse pulp and paper properties

The effect of depithing levels on bagasse soda pulping and its pulp and paper properties were studied in Pars paper factory. Bagasse with different levels of depithing (i.e. bagasse with 30, 20, 10, 5 and 0 % of pith) were cooked under the same pulping condition as used in pars factory: chemical charge 15% of sodium hydroxide (NaOH applied based on dry fibre), temperature: 170 °C, cooking time: 15 minutes and L:W= 10:1. Effects of different level of pith on residual active alkali and pulp and paper properties were investigated. Results have shown that by pith level decreasing in raw material, the residual active alkali in black liquor increased and pulp properties such as kappa number, screen yield, shive content, initial freeness and drainage time improved. Also, strength properties of paper such as tear, burst and tensile increased. In addition, comparing these results to pulping conditions of above factory indicated that the efficiency of factory depithing process is very low. Therefore, its effect appears in high level of pith and consequently high chemical consumption in digester and hence contributes to the inferior quality of pulp and paper properties.