Study on Refining Performances in Chemi-mechanical Pulping of Mixed Poplar and Eucalypt Woodchips

The refining performances of mixed poplar and eucalypt woodchips (mixture ratio 6:4) were investigated at medium and high pulp consistency via chemi-mechanical pulping (CMP). The specific refining energy consumption (SEC), fiber fraction proportion, and Canadian standard freeness (CSF) were determined to evaluate the effects of pulp consistency and NaOH dosage on the refining performances of mixed poplar and eucalypt woodchips. While the dosage of NaOH for impregnation was maintained constant, the SEC and shive content increased with increasing pulp consistency. Different fractions obtained from the Bauer-McNett classifier showed that higher pulp consistency could be expected to yield more long fibers and shive in the stock. Upon increasing the NaOH dosage, the shive content and SEC reduced significantly. When the NaOH dosage was increased to 6%, the results indicated that it was difficult to reduce the shive content to less than 1% at high pulp consistencies (25%~35%), whereas 0.18% shive fraction could be achieved at a medium pulp consistency (15%).