Abstract

This article describes a theoretical method of linking fastener corrosion in wood connections to potential reduction in lateral shear strength. It builds upon published quantitative data of corrosion rates of metals in contact with treated wood for several different wood preservatives. These corrosion rates are then combined with yield theory equations to calculate a loss in lateral capacity as a function of time. The calculations are straightforward and can be performed in a spreadsheet or simple computer program. They can accommodate time-dependent and moisture-dependent corrosion rates. The latter of these capabilities can easily be recognized as important, inasmuch as corrosion rates of fasteners are recognized as being dependent on moisture content of the wood in which they are embedded. The calculation method is dependent on corrosion rate, and the method is therefore limited by the lack of agreement in corrosion rates presented in the literature. Within these limitations, the article examines how different corrosion rates and changes in corrosion rates affect the mechanical properties and service life of nailed wood joints.

Abstract

There is currently no ASTM standard for testing the tensile mechanical properties of strands used in wood-strand–based composites. In this study we compared the ultimate tensile strength (UTS) parallel to grain and tensile modulus of elasticity (MOE) for southern pine (Pinus spp.) wood strands from an oriented strand board plant in which one treatment consisted of rectangle-shaped specimens and the other treatment consisted of samples milled into a tapered (“dog-bone”) shape. For bone-shaped samples, the measurements observed were 16 and 27 percent higher for MOE and UTS, respectively, than for the rectangular samples, and this was attributed to the generally accepted fact that dog-bone–shaped geometry yields measurements that are closer to true population parameters. Variation in mechanical properties was not statistically different for the two test methods. This study quantified that tensile testing of the rectangular strands will underestimate the true strength and MOE of the southern pine material. Because both methods resulted in similar levels of variability in test results, in-plant testing, using the traditional rectangular sample, may be acceptable for quality control as long as there is a recognition that the UTS and MOE values will be substantially more underestimated than those of smaller, dog-bone–shaped samples. As such, for future standards development, consideration should be given to the geometry of the strand when determining mechanical properties. Given the large amount of studies that use rectangular strands, there may be a need for a methodology to relate test results for rectangular and bone-shaped specimens.

Abstract

The purpose of this study was to investigate the vibrational properties and corresponding anisotropicity in wood during different states of moisture sorption. Samples of maple (Acer spp.) and red oak (Quercus rubra Michx.f.) were moisture conditioned by the adsorption process from an ovendried state and by the desorption process from a water-saturated state. The dynamic modulus of elasticity (DMOE) and logarithmic decrement (δ) were examined as a function of grain orientation during moisture change processes and under constant moisture contents (MC). It was observed that regardless of species and grain direction, the DMOE and δ were lower and higher, respectively, during the moisture change process compared with those measured without a change in MC. The increase in δ value during adsorption was greater than that during desorption. These results suggest that wood in an unstable state shows lower elasticity and strength and higher damping properties than wood in an equilibrium state. Furthermore, results of this study demonstrate that a greater adsorption rate leads to greater destabilization during an adsorption process. The anisotropy in vibrational properties was found to vary between two species.

Abstract

Fourteen stains were tested in the laboratory to compare water uptake and leaching reduction of wood treated with chromated copper arsenate, alkaline copper quat, and copper azole. Based on results of a 2-week test, eight stains were selected to be evaluated over 3 months of accelerated weathering and five stains over 3 years of natural exposure in Toronto, Ontario, Canada. These comparisons were made in order to find a quick and reliable method for replacing natural exposure tests.

Comparison of different weathering techniques showed significant correlations between leaching and water uptake results from laboratory tests and natural weathering. The cumulative percentage of inorganic elements leached from coated samples was highly correlated with the cumulative percentage leached during 3 years of natural weathering. Also, the average moisture content of treated-coated samples after 1 and 3 days of water immersion showed a relatively strong positive correlation with the average moisture content of treated-coated wood samples during wet periods of natural weathering (moisture content above 20%, average of 17 reading times). Thus, this quick laboratory test is a reliable short-term test for evaluating the ability of coatings to reduce leaching and water uptake when applied on preservative-treated wood.

Abstract

Wood-based boards were exposed to an outdoor environment at angles of 90° and 45° to the ground surface in order to investigate the effect of exposure angle on board properties. In a study on 5-year outdoor exposure, the effects of the exposure angle varied depending on the type of board. Particleboard (PB) and oriented strand board (OSB) deteriorated faster when exposed at 45° compared with 90°, and the difference was more apparent with longer exposure. Five years of exposure at 45° lowered the retention of the modulus of rupture and internal bond of phenolic resin–bonded PB to 15 and 4 percent, respectively. In contrast, medium-density fiberboard (MDF) showed no difference in deterioration between both exposure angles. After 5 years of exposure, the retention of the modulus of rupture was 70 to 80 percent in MDF, while that of internal bond was 81 to 97 percent, thereby showing that the internal bond was better retained than the modulus of rupture. The high durability of MDF was attributable partly to its smoother surface compared with the other boards, which prevented residual rainwater on the surface from infiltrating into the board. Conversely, PB and OSB were prone to surface weathering, which led to the ingress of rainwater. The resultant swelling resulted in the collapse of bonding points, followed by the formation of voids inside the boards. Residual moisture in the voids then caused decay as well as a further reduction in strength (biodegradation).

Abstract

The Young's modulus and shear modulus of solid wood (Sitka spruce, Picea sitchensis), medium-density fiberboard (MDF), and Lauan wood (Shorea sp.) with five-ply construction were determined by conducting flexural and longitudinal vibration tests with various specimen depth/length ratios and performing a subsequent finite element analysis (FEA). The values of Young's modulus and shear modulus were calculated by three analysis methods: (1) the method based on the rigorous solution of Timoshenko's differential equation (Phil. Mag. 41:744–746, 1921), (2) the iteration procedure proposed by Hearmon (Brit. J. Appl. Phys. 9:381–388, 1958), and (3) the method in which Young's modulus measured by the longitudinal vibration test is substituted into an approximated equation proposed by Goens (Ann. Physik. Ser. 7 11:649–678, 1931). The results obtained from the FEA suggested that the analysis method does not influence the values of Young's modulus or shear modulus. However, the results obtained indicated that the analysis method influenced the measured values of these moduli. Although Method 3 is simpler than Methods 1 and 2, the influence of depth/span ratio was more pronounced when using resonance frequencies lower than the second flexural vibration mode. When using the resonance frequency for flexural vibrations higher than the third mode, however, it is promising that the shear modulus can be measured while reducing the influence of the depth/length ratio.

Abstract

Bio-oil obtained from the pyrolysis of pine wood was mixed with polymeric diphenylmethane diisocyanate (pMDI) to form an adhesive binder system for flakeboard. Acetone was added for reducing the viscosity of the adhesive system. The thermal properties and curing behavior of five different adhesive mixes were examined using dynamic mechanical analysis (DMA). Temperature scans were performed in a range of 50°C to 200°C with a heating rate of 10°C/min, frequency of 1 Hz, and strain amplitude of 15 μm. Results indicated that less time was needed to reach the maximum storage modulus of the adhesive mix with an increase in bio-oil content. The adhesive with the pMDI/bio-oil ratio of 25/75 presented the fastest curing speed but the lowest modulus value at temperatures of approximately 100°C. The pMDI-acetone adhesive showed the best thermal mechanical properties among the five adhesive binder systems.

Abstract

Urea-melamine-formaldehyde (UMF) resins were synthesized and used for manufacturing medium-density fiberboard (MDF). As melamine content was increased at the same formaldehyde/urea (F/U) molar ratio, the solids content of the resin increased. Physical properties and storage stability of the resins tended to improve slightly when the final pH of resin was 8.5 compared with 7.5 and 9.5. At the same F/U molar ratio, free formaldehyde content and gel time of the resins decreased as melamine content increased. Chemical structures of the resins were proposed from the results of ¹³C nuclear magnetic resonance and Fourier transform infrared analyses. Formaldehyde emissions of MDF prepared with UMF resins with the same F/U molar ratio decreased as melamine content of resin was increased. MDF fabricated with UMF resin showed slightly better resistance against decay fungi and termites compared with MDF fabricated with urea-formaldehyde (UF) resin. Other physical properties of MDF fabricated with UMF resin were comparable to those of MDF fabricated with a commercial UF resin. An optimum F/U molar ratio of 1.2 with melamine content of 15 percent, equivalent to an F/(U+M) molar ratio of 0.98, was found from the results.

Abstract

China is the largest furniture exporter in the world. Its wood furniture industry has become an important part of the country's forestry economic development. Hence, investigating China's furniture industry cluster and export competitiveness would benefit the sustainable development of China's forestry industry. Our study indicates that, under the export-oriented strategy of China's reform and opened economy, the country's furniture industry has developed in three large areas over the last 30 years, namely, the Eastern Pearl River Delta, the Yangtze River Delta, and the Bohai Rim Region. As the strategy shifts from an export orientation to a focus on domestic demand, the country's midwestern area will take over China's industrial production. At present, China's furniture products have an important position in the world market. In 2010, furniture exports accounted for 27 percent of the world's total exports, with wood furniture accounting for US$10.6 billion worth of exports, or 58 percent of China's total exports of furniture. Among the main export markets, the United States accounted for 39 percent of China's total exports. In terms of international furniture trade, an important mutual relationship exists between China and the United States. China's office furniture and kitchen furniture have price advantages, whereas the bedroom furniture lacks price advantages. In particular, the production and export of mahogany furniture may be hampered by raw material shortage because of the protection of tropical forest resources. This challenge puts China's furniture industry in future competition with emerging countries such as Malaysia.

Abstract

Forest operations generate large quantities of forest biomass residues that can be used for production of bioenergy and bioproducts. However, a significant portion of recoverable residues are inaccessible to large chip vans, making use financially infeasible. New production systems must be developed to increase productivity and reduce costs to facilitate use of these materials. We present a comparison of two alternative systems to produce biomass fuel (i.e., “hog fuel”) from forest residues that are inaccessible to chip vans: (1) forwarding residues in fifth-wheel end-dump trailers to a concentration yard, where they can be stored and then ground directly into chip vans, and (2) grinding residues on the treatment unit and forwarding the hog fuel in high-sided dump trucks to a concentration yard, where it can be stored and then reloaded into chip vans using a front-end loader. To quantify the productivity and costs of these systems, work study data were collected for both systems on the same treatment unit in northern Idaho in July 2009. With standard machine rate calculations, the observed costs from roadside to loaded chip van were $23.62 per bone dry ton (BDT) for slash forwarding and $24.52 BDT⁻¹ for in-woods grinding. Results indicate that for harvest units with conditions similar to the test area, slash forwarding is most appropriate for sites with dispersed residues and long-distance in-woods grinder mobilization. For sites with densely piled roadside residues, in-wood grinding is likely to be a more productive and less costly option for residue recovery.

Abstract

The influence of Pinus radiata bark polyphenol components in the phenol liquefaction of P. radiata bark was investigated using p-toluene sulfonic acid (PTSA) and sulfuric acid (SA) as acid catalysts. A series of the phenol liquefaction reactions were carried out using mixtures of pure cellulose with increasing amounts of hot-water extract (HWE) of P. radiata bark—the polyphenol-rich component of bark. The yields of liquefied product reactions and combined phenol amounts in them were determined, and the liquefaction residues were also analyzed for determination of acid-soluble and insoluble polyphenols and residual cellulose fractions.

The yield of cellulose liquefaction decreased linearly with increasing amounts of HWE with the effect being more pronounced for SA than for PTSA. The combined phenol amount increased with liquefaction yield increases for both SA and PTSA catalysts, but at liquefaction yield levels above 83 percent, more phenol was combined for SA catalyst than for PTSA catalyst. The liquefaction residues contained lower cellulose and higher polyphenol components for SA catalyst than for PTSA catalyst at the same liquefaction time. The results indicate that the bark polyphenol components can significantly interfere in the acid-catalyzed bark phenol liquefaction reactions by their excessive condensation with cellulose and/or phenol, especially in the presence of SA catalyst.