Dimensional Stability of Acetylated Aspen Flakeboard

This study was conducted to determine if thickness swelling of flakeboards, which is much greater than that of plywood or solid wood, can be improved by chemical modification of the constituent wood flakes prior to board manufacture. The chemical treatment involved acetylation of oven-dry aspen ring flakes with a 50/50 mixture of acetic anhydride and xylene. Thickness swell of treated and control samples was measured by either immersion in water for periods of up to 10 days or exposure to 90% relative humidity for periods of up to 20 days. Treated samples exhibited one-sixth to one-seventh the thickness swelling of controls for the water-soak test. Similar trends were observed for humidity exposure

Thermal Degradation of Wood Fibers During Hot-Pressing of Mdf Composites: Part I. Relative Effects and Benefits of Thermal Exposure

This research evaluated the potential of wood fiber to chemically decompose during hot-pressing. We evaluated changes in carbohydrate composition and structure as a function of multiple press temperatures (180°, 200°, and 220°C) and an array of hot-pressing durations from 180 to 2500 s. Results show how this thermal degradation in chemical composition directly results in changes in moisture sorption characteristics, physical and mechanical properties, and aboveground durability. For most mechanical properties, it appears that very little degrade occurs until mat temperatures exceed 150°C. Changes in the chemistry of medium density fiberboard seem to result in measurable changes in hygroscopicity, decay, strength, and stiffness. Control of hot-press temperature and duration appears a potential method to heat-treat medium density fiberboard and enhance its serviceability. This heat-treatment effect appears to be related to cumulative thermal load/exposure; subsequent analysis and computational modeling is currently underway

Properties of Hardboards Made From Acetylated Aspen and Southern Pine

The effects of fiber acetylation, resin content, and wax content on mechanical and physical properties of dry-process hardboard made from aspen and southern pine were investigated.Test results indicate that the modulus of rupture (MOR) and modulus of elasticity (MOE) of the hardboard specimens were decreased due to the fiber acetylation. Tensile stress parallel to face and internal bond (IB) were generally higher for untreated boards than for acetylated boards. Water absorption (WA) and thickness swelling (TH.S) were both reduced markedly by acetylation. In general, increasing resin content from 3% to 7% brought increases in MOR, MOE, tensile stress, and IB and improved WA and TH.S. Addition of the 0.5% wax content usually caused reductions in these mechanical properties, but improved WA and TH.S in some cases. Linear expansion (LE) in the dimensional stability test (from 30% to 90% RH) was significantly reduced by acetylation and influenced by wood species. Neither resin nor wax contents significantly affected the LE value of hardboard specimens in this study

CHAPTER 31 PERFORMANCE OF HARDBOARDS MADE FROM KENAF

This paper reports on the performance of dry-process hardboards made from pressurized refined whole kenaf stalks. Twenty hardboard panels were made from kenaf using 3% and 7% phenolic resin and 0 and 1.0% wax. Test results showed that nearly all mechanical and physical properties improved with increased resin content, but wax had a negative effect. Some property values met American National Standards Institute/American Hardboard Association (ANSI/AHA) A135.4 standards for Basic Hardboard while others did not. The results indicate that kenaf panels can be made to perform at acceptable levels for certain hardboard applications

The International Research Group on Wood Preservation

Conventional preservatives used to protect wood from insect and microbial damages are presently of major concern to human health and the environment. Finding alternative and economical preservatives has not been successful. Previous studies have shown that the resinous material extracted from the guayule plant (Parthenium argentatum, Gray) has both insect- and microbial-resistant properties. Unfortunately, it has not been accepted commercially because of the lack of an adequate supply of the raw material. However, the potential domestication of the guayule plant to produce hypoallergenic rubber latex will result in the production of large amounts of waste wood material. This should provide opportunity to use this natural source of the biologically resistant resinous chemicals. The objective of this preliminary study was to determine the effects of the rubber latex-removed wood residues or bagasse and the resinous extracts on termite- and decay-resistant properties. Two types of test materials were used in the study. One was wood impregnated with organic-solvent extracted resinous material from the plant. The other was composite wood fabricated using the residue or whole plant and plastic binder, which was used to improve the physical properties of the composite. Accelerated laboratory tests were conducted to determine the resistance of the wood products against the Eastern subterranean termite and wood fungi (brown-rot). The wood and stem of the guayule plant, wood treated with the resinous extract, and particle and composite wood made from ground guayule exhibited termite and wood fungal resistance. KEY WORDS: Brown-rot, decay, durability, extractives, fungus, guayule, bagasse, particleboard, specific gravity, termite, thickness change, weight loss, wood comp..

MEDIUM DENSITY FIBERBOARDS FROM PLANTATION-GROWN EUCALYPTUS SALIGNA Andrzej M. Krzysik, Research Specialist John A. Youngquist, Project Leader James H. Muehl, Forest Products Technologist

The production of industrial wood from natural forests is predicted to decline in the future. Factors that will contribute to this decline include changes in land use patterns, depletion of resources in some parts of the world, and the withdrawal of forest areas from industrial production in order to provide for environmental, recreational, and other social needs. There is a shortage of information on the suitability of fiber from many plantation-grown species for alternative composite products. This research was conducted to determine the suitability of plantation-grown Eucalyptus saligna from Brazil as a raw material for medium density fiberboards (MDF). Test panels of varying thickness (6, 13, and 19 mm) were made with 10% urea resin and 1% wax. Mechanical, water resistance, and dimensional stability properties were tested according to American Society for Testing and Materials (ASTM) standards. The results showed that nearly all mechanical properties of the panels at all thickness levels were above minimum requirements for MDF as specified in the ANSI-AHA and Euro MDF standards. These results indicate that MDF-type panels can be made from wood fiber derived from Eucalyptus saligna. Additional work is needed to ascertain the performance of MDF panels from this species through pilot and production scale trials