REINFORCEMENT AND OPTICAL-PROPERTIES OF SEPARATE AND CO-REFINED SOFTWOOD AND EUCALYPT MARKET KRAFT PULPS

The reinforcement strengths, optical properties and refining requireme nts of a eucalypt and several softwood market kraft pulps and blends a re described. Market kraft pulps examined are radiata pine pulps of lo w and medium coarseness, a benchmark pulp from the interior region of British Columbia, and a eucalypt pulp from Brazil. Eucalypt-softwood b lends are in proportions of 100:0, 50:50, 80:20, and 0:100 by mass, an d effects of separate and co-refining are assessed. The fibre qualitie s of unrefined softwood kraft pulps largely predetermine their refinin g potentials and handsheet strength and optical properties. The medium coarseness radiata pine and interior British Columbia pulps, based on their tear-tensile properties, have roughly equivalent reinforcement potentials. The low coarseness radiata pine pulp has somewhat lower re inforcement strength but has more web closure, improved optical proper ties, decrased refining energy requirements and improved sheet formati on. Tear-tensile properties of 80:20 eucalypt-softwood blends are roug hly the same and independent of the origin or type of softwood used. P ulps refined separately before blending have higher tear-tensile prope rties than those that are blended before co-refining. The light scatte ring coefficients are also similar for the 80:20 eucalypt-softwood ble nds. Co-refining of the eucalypt-softwood blends gives slightly higher light scattering coefficients than does separate refining of individu al blend components.