A Study of Loblolly Pine Growth Increments—Part V. Effects of Chemical and Morphological Factors on Tensile Behavior of Paper

Loblolly pine growth increments were divided into five fractions: two earlywood, a transition, and two latewood growth zones. Each fraction was kraft-pulped to four different time schedules, Valley beaten, made into handsheets, and investigated for tensile strength properties. Differences in tensile strength properties were related to inherent characteristics of individual tracheids. It was shown that the number of tracheids per unit volume of paper was the most important attribute to strength. Of secondary importance was the strength of the individual tracheid-to-tracheid bonds, which was influenced by residual lignin in the pulp. Using tensile energy values, the number of hydrogen bonds active in resisting tensile forces was estimated. This number was also related to the number of tracheids per unit volume as well as to residual lignin. The above variables were explained on the basis of the intraincremental chemical and anatomical properties of wood

Differentiation of Tracheids in Developing Secondary Xylem of Tsuga Canadensis L. Carr. Changes in Morphology and Cell-Wall Structure

The morphology and the changes in total cell-wall mass in developing secondary xylem of two eastern hemlock trees were studied. Sixty-μm-thick tangential-longitudinal sections were microtomed sequentially from the cambium through the currently developing and the one-year-old increments. The weight and volume of these sequential sections gave data on the rate of mass production. Cross-sectional microtome sections were used to study cell-wall structures and to measure cell-wall layer areas.Four tracheid maturation zones could be measured and described during both early- and latewood formations. The size of the cambium, cell enlargement zone, and the zone of S1 cellulose framework formation were the same throughout the growing season. However, the size of the zone of S2 cellulose formation changed. This zone was only one-third as wide during the formation of the thick S2 layer in latewood tracheids as it was during the formation of the thin S2 layer in earlywood tracheids. Despite the fact that the number of cells produced during S2 layer formation in latewood was only one-third as many as in the earlywood zone, the rate of total mass production was more than twice as great compared to earlywood. Tracheid diameters and cell-wall layer volumes across both the currently developing and the one-year-old xylem showed that size development is complete for each layer before the appearance of the next inner layer in the tracheids. However, cell-wall layer densities continued to increase perhaps well into the second and subsequent growing seasons. Change in the relative proportion of the cell-wall layers across the growth increment was not dominated by the S2 layer. This relative variation of the S2 layer was the smallest of any secondary cell-wall layer across the growth increment. However, it constituted 50-70% of the total cell-wall volume

The Effects of Previous Drying on Shrinkage and Moisture Content of Some Southern Bottomland Hardwoods

Three logs for each of nine southern hardwood species were obtained, and specimens were separated into heartwood and sapwood. Specimens were dried from the initial green condition to oven-dry and then resaturated and dried again to oven-dry. A simple linear regression analysis was performed to determine the relationship between volumetric shrinkage and moisture content of never-dried and previously-dried specimens. The average fiber saturation point was 33.3 (33.6 for sapwood and 32.9 for heartwood) for never-dried specimens and 29.4 (28.2 for sapwood and 30.6 for heartwood) for previously-dried specimens. An average of 86% of the variability in volumetric shrinkage of never-dried specimens can be attributed to moisture content, and 90.5% of the variability in volumetric shrinkage of previously-died specimens can be attributed to moisture content. Highly significant differences for the species factor were found to exist at an equilibrium moisture content of 90% relative humidity (RH) and 75% RH for both never-dried and previously-died specimens. Volumetric shrink-age differed significantly for species and wood-types at 90%, 75%, and 0% RH for previously-died wood and 75% and 0% RH for never-died wood. A t-test revealed significant differences between volumetric shrinkage of never-dried and that of previously-dried wood for both wood-types of two species and one wood-type of three others