Wood and Fiber Science (E-Journal)
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Manufacture of Wood-Cement Composites from Acacia Mangium. Part II. Use of Accelerators in the Manufacture of Wood-Wool Cement Boards from A. Mangium
Get PDFIn the second paper in this series, we test the hypothesis that cement-setting accelerators with the ability to chelate phenolic extractives will be more effective at improving the physical properties of wood-wool cement boards made from the heartwood of Acacia mangium than conventional accelerators. Furthermore, we assess whether the use of chelating accelerators will allow boards with acceptable properties to be manufactured from A. mangium wood-wool that has not been subjected to preliminary aqueous extraction to remove phenolic extractives. Batches of wood-wool from A. mangium containing approximately 75% heartwood were either soaked in water or used in their native form. The batches were then treated with an aqueous solution containing an inorganic compound (generally 0.05 or 0.1 M) selected for its ability to accelerate the hydration of Portland cement, and in the case of 5 of the 11 compounds tested, chelate phenolic extractives. Individual wood-wool cement boards were manufactured from each treated batch of wood-wool and tested for their dry and wet bending strength (MOR), stiffness (MOE), and water absorption properties. Boards made from untreated or water-soaked wood-wool acted as controls. The MOR and MOE of boards made from unsoaked A. mangium wood-wool and treated with the chelating accelerators tin or ferric chloride at 0.1 M concentration were 10.8 and 10.9 MPa and 2256 and 2178 MPa, respectively. These same boards showed less than 5% thickness swelling after 24-h immersion in water. In contrast most of the boards containing a conventional non-chelating accelerator had no structural integrity. The combination of a chelating accelerator and a conventional accelerator was particularly effective at improving the physical properties of boards made from unsoaked wood-wool. We conclude that wood-wool cement boards with acceptable physical properties can be manufactured from A. mangium heartwood by treating wood-wool with inorganic compounds that have the ability to chelate phenolic extractives and accelerate the hydration of Portland cement. Our findings could eliminate the need to pre-soak A. mangium wood-wool in water during the manufacture of wood-wool cement boards and may have broader relevance to the manufacture of wood-wool cement boards from other hardwood species containing phenolic extractives
Bioassaying Wood Preservatives with Aspergillus Niger
Get PDFThe bioassay with Aspergillus niger is a simple way of determining the presence and amount of pentachlorophenol or tributyltin oxide in wood, but it does not appear useful for measuring strongly fixed chemicals such as chromated copper arsenate, borate, and fluoride. Its effectiveness in detecting other preservatives has not been reported. Accordingly, the bioassay was evaluated for its ability to detect various concentrations of 15 preservatives introduced into blocks of ponderosa pine. These results were compared with those from modified soil-block tests involving the same chemicals. Several of the formulations—three quaternary ammonium compounds, copper naphthenate, and Folpet—imparted some decay resistance to the blocks but were not detectable with the bioassay. The remaining chemicals were all detectable, although sensitivities varied. These results suggest that the Aspergillus bioassay can be useful for detecting many wood preservatives
Verification of a Kinetics-Based Model for Long-Term Effects of Fire Retardants on Bending Strength at Elevated Temperatures
Get PDFThis study verifies a single-stage reaction-rate model for the long-term effects of various fire retardants. The adequacy of predictions from our previously reported models was tested using data from fire-retardant-treated wood exposed at 66°C (150°F) and 75% relative humidity for 3 or 4 years. Our analysis showed that if the treated wood experienced significant thermal degradation early during exposure to high temperature, then the previously reported model parameters adequately predicted thermal degradation for up to 4 years of steady-state exposure. However, if the treated wood did not experience significant thermal degradation early during high-temperature exposure, then the previous parameter estimates tended to underpredict degrade. Modified parameter estimates are presented where appropriate. This report also describes the practical implications of running the verified models for up to 10 annual iterations of an actual year of measured roof sheathing temperatures derived from structures exposed in the field. Our results predict that monoammonium phosphate, a generic fire-retardant formulation, can be expected to cause an additional 15% loss in original strength capacity in 10 years if used for roof sheathing under similar conditions
Douglas-FIR Bark. II. Isolation and Characterization of A Glucomannan
Get PDFA glucomannan has been isolated from the holocellulose fraction of the inner bark of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco], and its structure and physical constants have been determined. The molar ratio of o-mannose, d-glucose, and d-galactose was 2:1:0.3. The glucomannan was completely methylated and hydrolyzed. Gas-liquid chromatographic and mass spectrometric analyses showed the presence of 2,3,4,6-tetra-, 2,3,6-tri-, and 2,3-di-O-methyl-d-glucopyranose, 2,3,6-tri- and 2,3-di-O-methyl-d-mannopyranose, and 2,3,4,6-tetra-O-methyl-d-galactopyranose. The proposed glucomannan structure consists of a linear chain of β-d-(1 → 4)-linked mannose and glucose units with α-d-(1 → 6)-linked galactose as intermittent, single-unit branches. The structural and physical properties of this glucomannan place it within the alkali-soluble family of polysaccharides known to be contained in the wood of all gymnosperms
Effect of Ultrasonic Vibration on Convective Heat Transfer Between Water and Wood Cylinders
Get PDFA study has been conducted to examine the effect of ultrasonic vibration on convective heat transfer of wooden cylinders. Forty fully saturated and air-dried cylindrical wood specimens were partially submerged in a heated water bath of 59.8 C (with and without ultrasound). The temperature versus time relationship at the center of the cylinders was monitored. Results indicate that ultrasound significantly influenced the heat transfer to wooden cylinders
Dynamic Adhesive Wettability of Wood
Get PDFAdhesive wettability of wood is usually evaluated by contact angle measurement. Because of liquid penetration and spreading on the wood surface, the contact angle changes as a function of time. In this study, a wetting model was developed to describe the dynamic contact angle process in which a parameter (K) can be used to quantify the adhesive penetration and spreading during the adhesive wetting process. By applying the wetting model, the adhesive wettability of sapwood and heartwood of southern pine and Douglas-fir was studied. Liquid wettability along and across the wood grain direction was also compared. Two resin systems, polymeric diphenylmethane diisocyanate (PMDI) and phenol-formaldehyde (PF), were evaluated. It was learned from this study that the wetting model could accurately describe the dynamic adhesive wetting process on wood surfaces. Through applying this model, it is shown that PMDI resin exhibited a better wettability on wood than PF resin. The adhesive is more easily wetted along the grain direction than across the grain direction. Species and drop location have no significant effect on the spreading and penetration rate (K-value). However, the interaction term between species and resin type shows a significant effect for the K-value. PMDI exhibits a greater K-value on the Douglas-fir surface, while PF resin shows a greater K-value on the southern pine surface. Heartwood shows a lower instantaneous contact angle than sapwood. Douglas-fir has a greater instantaneous contact angle than southern pine. The effect of species on the equilibrium contact angle is strongly dependent on the location of the drop on the wood surface. The equilibrium contact angle of Douglas-fir is smaller than that of southern pine for sapwood, but is greater for heartwood
Distribution of Toxic Elements in Douglas-Fir Plywood Treated with Czaa Preservative
Get PDFFifteen Douglas-fir plywood panels were treated with a copper-zinc-arsenic additive preservative (CZAA) in an ammoniacal solution in a full-cell process. Individual plies from the centers of the treated panels were assayed for CuO. ZnO, and As2 O5 on the basis of Cu, Zn, and As content by atomic adsorption spectrophotometry. Retentions of preservative oxides and their distribution in the plies as judged from copper-containing compounds indicated that treated panels could be well protected against biodegradation.Microscopic identification of species revealed that inner plies were made from fir, spruce, and hemlock. The preservative in them, monitored by copper-containing compounds, was evenly spread in the core plies
Finite Element Fracture Prediction For Wood With Knots and Cross Grain
Get PDFA finite element/fracture mechanics model has been developed to predict the tension behavior of structural wood members containing defects. The computer code Starwx presented here is used in a preliminary investigation of the effect of global cross grain on the strength of structural wood members with knots. The results indicate a more severe stress condition for the member with global cross grain as compared to the straight grain member.A method of strength prediction is presented that, unlike other methods, simulates the progressive fracture/failure process in wood, which leads to the ultimate load-carrying capacity of the member. Program Starwx is employed to predict the failure of a wood member containing a knot and global cross grain in a case for which actual test data are available. The member ultimate strength predicted was within 15% of the strength determined by the test
Creep Behavior of Flakeboards Made with a Mixture of Southern Species
Get PDFDeflection of oriented flakeboards, random flakeboards, and southern pine plywood was evaluated for small size bending specimens and concentrated loads applied to panels nailed on framing lumber. The flakeboards contained a mixture of southern hardwoods and pine; the plywood was 3-ply 1/2-inch and 4-ply 5/8-inch construction. Tests of both panel directions, all load levels and RH cycles showed plywood bending specimens with the smallest deflection increase, and both random and oriented flakeboard bending specimens showed more increases. The plywood relative creep averaged 1.76; the flakeboard relative creep averaged 2.26 and 2.30 for oriented and random construction, respectively. For the concentrated loading, oriented flakeboard panels with the smallest initial deflection had the largest creep after 32 days. Random flakeboard and plywood showed less creep
Assessing the Effect of Swelling Pressures in Particleboard and MDF Using Acoustic Emission Technology
Get PDFThe interaction of moisture with wood-based composites leads to the development of swelling pressures that cause the failure of resin bonds and the dislocation of fibers within the composites. These bond failures and dislocations can result in abrupt stress changes that trigger vibrations and create acoustic emissions (AE). Resin and wax levels within the composites effectively limit the interaction of wood and water and affect the level of AE. In this research, acoustic emissions were used to measure the effects of resin and wax levels in both particleboard and medium density fiber-board (MDF).Two resin levels and three wax levels in the composites were tested. Samples were immersed in distilled water for 120 min during which cumulative AE were recorded. In addition, the density and moisture content gains of the samples were determined.The results provide evidence that both resin and wax levels significantly affect the number of acoustic emissions and the failure of internal bonds within the samples. Increasing the percentage of wax reduced the level of acoustic emissions in both the MDF and particleboard. Increasing the percentage of resin significantly affected the levels of AE in both MDF and particleboard, although in different ways because of the differences in internal structure within the composites. Acoustic emission technology could be a useful tool in assessing the quality and consistency of the composites