Efforts were made to reduce shives content and refining energy in producing refiner mechanical pulp (RMP) from bark containing 22% core (bark22) by varying two operating parameters, raw material soaking temperature and refining consistencies, which were changed from 40-85 °C and 10-20% respectively. 2~2 factorial design was used for determining various combinations of raw material soaking temperature and refining consistency. Bark22 was refined on a 300 mm Sprout-Bauer refiner in several passes to get a CSF of around 125 ml. Analysis of data and subsequent regression equations developed indicated that soaking temperature did not have any significant effect on various pulp properties. Pulp properties were mainly dependent on the refining intensity and the residence time, which determined the degree and extent of fiber cutting and fibrillation. Data analysis indicated that refining energy and pulp shives content decreased with an increase in soaking temperature. Energy reduction could be because of softening of core at higher temperature. Bleaching study has shown that bark22 mechanical pulps can be bleached to newsprint level brightness with a small amount of hydrogen peroxide and sodium hydroxide. For higher grades' application, pulp can be bleached efficiently to more than 75 % brightness level with approximately 4% and 3% H_2O_2 and NaOH dosages.
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