ALKALINE PEROXIDE MECHANICAL PULPING OF HARDWOODS

The growth of chemithermomechanical pulping (CTMP) with prebleaching has brought about many new developments in ways to brighten the high-yield pulp made in the conventional sulfite or alkaline sulfite pretreatment processes. In 1989, Andritz Sprout-Bauer introduced its "alkaline peroxide mechanical pulping" process as an improvement to the conventional prebleach CTMP process. In the process, the chips can be fully bleached before refining by impregnating them with peroxide bleach liquor. Many of the same variables that affect pulp bleaching-washing, consistency, temperature, and chemical charge-also influence chip bleaching. Bleaching and pulping the chips before refining reduces energy consumption and eliminates the need for a separate bleach plant. The process was used on an aspen furnish and a mixed furnish of Southern hardwoods, and the authors report that both furnishes showed energy savings in comparison with bleached CTMP and strength properties that met or equaled those of bleached CTMP.