Effect of Softwood Morphology and Chip Thickness on Pulping with Displacement Kraft Batch Cooking, 1996 Pulping Conference Proceedings

M.Svedman

M. Luhtanen

Sunds Defibrator Pori Oy

P. Tikka

SciTech-Service Inc.

The role of softwood raw material quality in kraft pulping is generally acknowledged. Nevertheless, most studies and mills only use the wood raw material by species without any information on the botanical and morphological background. In addition, chip size distribution may vary significantly. The present pulping study will focus on the effect of species, wood age and chip thickness on modem kraft pulping. Well defined trees of Pinus Sylvesfris (Scats Pine) and Picea Abies (Norway Spruce) were cut, debarked by hand and chipped by a pilot chipper. Tree selection was segregated into various categories, (1) pulpwood containing mature wood and older thinnings and (2) young wood containing first thinnings and top wood. In contrast to these dominating Scandinavian softwoods cut pulpwood of Pinus Taeda (Loblolly Pine) from the south-east coast of the USA was used. Displacement kraft cooking of chips with harmonized particle size distributions as well as stratified thickness fractions was carried out. Cooking was adjusted to result in constant residual black liquor alkali and two kappa number levels, 15 and 30. The pulps were then analyzed, bleached using an 0-D(EOP)DED sequence and analyzed again. The numerous findings in cooking characteristics, bleachability and pulp quality including strength and optical properties will be discussed. For instance, younger wood gave lower yield and lower pulp strength, but best optical properties; Scats Pine showed best bleachability; Norway Spruce pulps had the best reinforcing ability; Loblolly Pine was more difficult to cook and bleach compared to Scandinavian pine and spruce. Cooking studies with stratified chip thickness fractions showed retarded delignification as chip thickness increased, but clear non-uniformity in the form of reject generation showed up only with chip thicknesses of over 8 mm.