A Study of Loblolly Pine Growth Increments—Part III Refining Characteristics of Tracheids from Kraft Pulps

Geza Ifju, Peter Labosky, Frank D. Mitsianis

Abstract


Growth increments of loblolly pine were divided into five growth zones and kraft-pulped according to four different digestion schedules of 1 1/2, 1 3/4, 2, and 3 hours. Each of the 20 pulps was subjected to four periods of beating and Canadian Standard Freeness (CSF) was determined for each. It was found that all pulps independent of the extent of digestion or origin of wood from the growth ring had about the same CSF after short periods of beating. After 35 minutes in the beater, latewood pulp freeness was drastically reduced whereas earlywood pulps changed very little. In general, significantly less energy, as indicated by shorter beating times, was needed for latewood pulps to achieve a specific CSF level than for earlywood pulp. Pulps of low yield were easier to refine than those of high yield. Scanning electron microscopic observations revealed that all pulps underwent a tracheid cell-wall peeling sequence. The layer removed from latewood tracheids by beating separated into long fibrillar bundles while earlywood lamellae freed from tracheids remained intact. The influence of this external fibrillation was attributed to differences between the pulps in refining.

Keywords


<i>Pinus taeda</i>;beating;cell wall layers;earlywood;fibrillation;freeness;growth rings;kraft pulps;lamellae;latewood;SEM;fiber structure

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