Chemical Degradation of Wood: The Relationship Between Strength Retention and Pentosan Content

This investigation resulted from a prior study on the effect of acids and alkalis on wood. In that study, indirect support was given the contention that a low original pentosan content in wood favors resistance to chemical degradation. In the present study, the relationship of pentosan content and its retention to the resistance of wood to chemical attack is quantitatively established. A low original pentosan content and a high pentosan retention correlate well with resistance to acid degradation as measured by strength retention. The relationship between these two pentosan values and alkaline degradation is weaker, but still significant. Hemicellulose retention is a better indicator of the behavior of wood with respect to alkaline attack. The most useful result is the fact that, through chemical analysis for pentosans in a wood, resistance to chemical degradation can be indicated

Wood for Structural and Architectural Purposes

This paper reports the findings and conclusions of Panel II on Structural Purposes, Committee on Renewable Resources for Industrial Materials (CORRIM), National Academy of Sciences/National Research Council. The Panel examined the use of wood for structural purposes and its conversion from standing trees to primary structural commodities as of 1970, and from this base year developed projections of use to the years 1985 and 2000. Concerns of the Panel included the availability of the renewable resource, the demand for wood products, and particularly the costs in terms of manpower, energy, and capital depreciation involved in production and transportation to the point of use. Comparable data from source to end commodity were compiled for other structural materials including steel, aluminum, concrete, brick, and petrochemical derivatives.Wood products were found, with few exceptions, to be more homogeneous than nonwood-based commodities in man-hour and capital requirements. However, the most notable differences between wood-based and nonwood-based commodities are in their energy requirements. Commodities based on nonrenewable resources are appreciably more energy intensive per ton of product than are their wood-based counterparts. In part, this is the result of energy self-sufficiency in the manufacturing process attained through the use of wood residues as fuel

Mechanisms of Cell-wall Growth in Secondary XYLEM

Current concepts of the growth of the cell wall in secondary xylem are briefly reviewed. Following a description of the organization of the mature cell wall, its development is traced from initiation in the cambial zone to maturity. Multinet growth and various concepts concerning the origin of microfibrils are discussed

Variation in The Cell-Wall Density of Wood

The density of wood substance determined pycnometrically in water for 18 species was found to range from 1.508 to 1.542 g/cc. After correction for perturbation or compression of the sorbed water, wood-substance density values ranged from 1.497 to 1.517 g/cc for hardwoods and from 1.517 to 1.529 g/cc for the softwoods studied. Specific volume of wood substance ranged from 0.654 to 0.668 cc/g.Specific volume of the dry cell walls was determined pycnometrically in toluene, using 1-mm sections and wood meal. Values obtained with wood meal were more reliable because of incomplete cell cavity penetration in 1-mm sections and ranged from 0.668 to 0.698 cc/g. Optically estimated values of specific volume based on microtome sections were usually considerably higher as a consequence of the aberrant shrinkage behavior of microtome sections as compared with blocks of wood. Calculated as the difference between specific volumes of cell wall and wood substance, voids in the dry cell walls of these 18 species occupied from 1.64 to 4.76% of cell-wall volume. Swollen cell-wall specific volumes derived by means of an optical technique, the validity of which has been questioned, ranged from 0.894 to 1.206 cc/g, implying water-filled voids in swollen cell walls ranging from 0.231 to 0.546 cc/g.Variation in specific volume of wood substance, and particularly in specific volume of dry cell walls, accounted for significant amounts of variation in strain behavior among these 18 species. In bending, tension, and compression parallel to grain, the effect of high specific volume is to increase strain at maximum load. The increase was manifest only beyond the proportional limit. This is the region of large plastic deformation, and it may be assumed that woods having cell walls of low density are more susceptible to time-dependent effects such as creep and relaxation.Within proportional limit, the effect of increasing specific volume of cell walls is to decrease the efficiency of the cell wall in response to stress. The ratio of proportional limit to ultimate stress, at least in bending and tension, decreases similarly as the specific volume of wood substance and cell wall increases