Refining High-yield Pulp and NBSK for Papermaking Application, 2016 International Mechanical Pulping (IMPC) Conference

Driven by quality improvement and cost reduction, high-yield pulp (HYP) or Bleached Chemi-thermomechanical pulp (BCTMP) has been widely used to substitute chemical pulps in various paper grades. However, there is no information available to guide HYP users to choose the right low-consistency refining conditions in order to maximize the benefits of HYP in paper.

In this study, a series of low-consistency refining trials of SW HYP and NBSK were carried out, aiming to identify the difference of co-refining and separate refining of HYP/NBSK and the impact of these two refining methods on HYP/NBSK properties. Results show that compared to separate refining, co-refining of HYP/NBSK requires less refining energy to achieve the same freeness level, and the obtained pulps have similar bulk, tensile, and PPS roughness. 50% SW HYP substitution to NBSK significantly increases the furnish bulk before refining. At the same freeness, HYP/NBSK has a higher bulk and roughness but lower tensile than the NBSK alone. At the same refining energy, HYP/NBSK still has a higher bulk than NBSK. Interestingly the tensile and Scott Bond of HYP/NBSK are similar to NBSK when HYP/NBSK is co-refined at an energy lower than 40 kWh/t. Finally, at the same bulk, HYP/NBSK has a higher tensile but lower roughness than NBSK.

In general, to reach the same freeness as refining of NBSK alone, co-refining of HYP/NBSK can be used to reduce refining energy and to minimize the loss of tensile. On the other hand, if the same energy is used for HYP/NBSK as refining NBSK alone before HYP substitution, then separate refining can be used to maximize the bulk of the HYP/NBSK furnish.

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