Mechanical Pulping by Fractionation After Low Energy Refining, 1993 Pulping Conference Proceedings

Recent research has indicated that in the initial stages of refining, energy is selectively absorbed by the earlywood portion of the annual growth increment. To evaluate the implications of this result, loblolly pine wood chips have been refined at very low energies and fractionated on a 10 mesh screen. The retained 10 mesh fraction should be enriched in latewood fibers, and the pass 10 mesh fraction enriched in earlywood fibers. Each fraction was then further refined to usable freeness levels and the resulting pulps compared to samples prepared using normal refining procedures that are without interstage fractionation. Juvenile whole chip requires 15 to 20% more energy to obtain the same Tensile Index as mature whole chips. Mature pulp retained on the 10 mesh screen has the same specific energy requirements to constant Tensile Index as the mature whole chips, but the pass 10 mesh fraction requires about 12% more energy to obtain the same strength. Both the juvenile wood pass 10 and retained 10 mesh samples require leas energy to obtain a constant tensile index than the juvenile whole wood chips, and have about the same specific energy requirements as the mature wood sample.