Wood and Fiber Science (E-Journal)
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Sensitivity Study of a Numerical Model of Heat and Mass Transfer Involved During the Medium-Density Fiberboard Hot Pressing Process
Get PDFThe objective of this work was to estimate the impact of the variability of the medium-density fiberboard mat heat and moisture transfer properties on the results predicted by a numerical model of hot pressing. The three state variables of the model, temperature, air pressure, and vapor pressure, depend on parameters describing the material properties of the mat known with a limited degree of precision. Moreover, different moisture sorption models and initial moisture contents also have an impact on the numerically predicted results. In this sensitivity study, we determined the impact of variations of the mat properties, sorption models, boundary conditions, and initial MC on the state variables. Our study shows that mat thermal conductivity, convective mass transfer coefficient of the external boundary, and gas permeability have the most significant impact on temperature, gas pressure, and MC within the mat. On the other hand, the convective heat transfer coefficient of the external boundary has no impact on the state variables. The sorption model affects significantly mat MC predictions only. The initial MC of the mat has a strong influence on the internal gas pressure
Acrylate Wood Densification: Effects of Vacuum Time and Nanoparticles on Chemical Retention, Penetration, and Resin Distribution
Get PDFThe feasibility of preparing a surface-densified wood product by replacing the traditional time-consuming pressurization stage with only a short vacuum time was investigated. Sugar maple and red oak wood specimens were successfully impregnated with low-viscosity resins of 1,6 hexanediol dimethacrylate and trimethylolpropane trimethacrylate, with or without silicate nanoparticles, using vacuum times of 30 s to 10 min without pressurization. Chemical retention (CR) and vertical density profiles of the treated wood specimens were measured. The CRs obtained with the short vacuum impregnation process, even with a vacuum of 30 s or 60 s, proved comparable to those achieved by the traditional process of 30-min vacuum plus 30-min pressure. A 52-63 wt% CR was found for maple impregnated with neat resin, while the formulations containing nanoparticles achieved 44-55 wt% as the vacuum time was increased 30 s to 10 min. Oak yielded lower CR values. The vertical density profiles indicated better treatability for maple than oak. Examination of the resin and resin/nanoparticle penetration into the wood by scanning electron microscopy revealed successful wood impregnation with both nanoparticles and resin
Technical Note: Effects of Nanoclay Addition to Phenol-Formaldehyde Resin on the Permeability of Oriented Strand Lumber
Get PDFThis note examined the effects of adding nanoclays to phenol-formaldehyde resin during the manufacture of oriented strand lumber (OSL) on its in-plane permeability. The panels were made from mountain pine beetle (MPB) attacked lodgepole pine (Pinus contorta) strands. Three different montmorillonite nanoclays were mixed with the PF resin: Na+, hydrophobic organics modified 10A, and hydrophilic organics modified 30B. None of the nanoclays changed the permeability of OSL significantly. The MPB-OSL had higher in-plane permeability than those conventionally made from aspen, which indicated that the pressing time could be shorter for MPB-OSL compared with OSL made from MPB-free strands
Effect of Panel Density on Major Properties of Oriented Strandboard
Get PDFAn extensive experimental study was carried out to systematically investigate the influence of panel density on oriented strandboard (OSB) properties. Nine sets of 711 × 711 × 11.1-mm aspen OSB panels with a target density varying 449-705 kg/m3 were manufactured. The panels were tested for major properties, including modulus of rupture (MOR), modulus of elasticity (MOE), internal bond strength (IB), water absorption (WA), and thickness swell (TS) after 24-h soaking and rolling shear strength (RS). The results indicated that, in general, panel density positively affected the properties of the OSB panels. Effects of panel density on parallel MOR and MOE, IB, and RS were nonlinear and could be described with convex quadratic curves. TS and WA linearly decreased with increasing panel density
Montmorillonite Nanoparticle Distribution and Morphology in Melamine-Urea-Formaldehyde Resin-Impregnated Wood Nanocomposites
Get PDFAttempts were made to investigate nanoparticle distribution in aspen by using electron probe microanalysis (EPMA) and Wincell software analysis to detect and analyze aluminum elements of impregnated montmorillonite (MMT) nanoclays. The cross-section morphologies of both untreated and nanoclay/melamine-urea-formaldhyde (MUF)-treated wood samples were characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM). With the combination of EPMA and TEM, it was demonstrated that nanoparticles were distributed through the wood cell wall structure. Wood cell walls functioned as filters or sieves to capture nanoparticles, especially in the compound middle lamella and the external layer of the secondary wall (S1) to form a nanoparticle distribution network. The interphase interaction and adhesion between MMT and MUF resin was characterized by AFM observation. Organophilic montmorillonites showed better interphase interactions than the pristine untreated hydrophilic MMT nanoparticles. It was confirmed that the functional groups on the surface of MMT play an important role in the compatibility between MMT nanoclay and MUF resin, which have a strong influence on the physical/mechanical properties of the resulting nanoclay/MUF wood nanocomposites
Process Zone Length and Fracture Energy of Spruce Wood in Mode-I from Size Effect
Get PDFThis article reports on the determination of fracture energy and fracture process zone length in Mode I fracture of European spruce wood loaded in tension perpendicular to the fiber direction based on Bazant's size effect law. Within the size effect model, fracture energy and fracture process zone length are correlated and represent unambiguous limit values for large structures or specimens. The model parameters were derived from an earlier experimental size effect study on specific single-edge notched beam specimens with a scale range of 1:32. The Mode I fracture energy range of 250-290 N/m, derived from the size effect law, is in agreement with fracture energies obtained for the same specimens based on external work to complete specimen failure. The elastically equivalent length of the fully developed fracture process zone ahead of the nominal crack tip was determined to be in the range of about 2 mm. The stated independent proof of the correlated fracture energy confirms the validity of the derived size of the fracture process zone. Furthermore, fracture process zone size obtained is in close agreement with a previous result for eastern Canadian spruce, a finding based on scanning electron microscopy
The Ability of Wood to Buffer Highly Acidic and Alkaline Adhesives
Get PDFThe ability of wood to buffer and mitigate the effects of strongly acidic or alkaline environments produced near the glue line by extreme pH structural adhesives was evaluated. The pH values of wood, cured adhesives, and mixtures of the two in water slurries were determined for different wood types. The pHs of slurries of seven highly alkaline phenol-formaldehyde adhesives were lowered when the adhesive was cured in the presence of wood dust with effects increasing with the proportion of wood in the mixture. The "acidities" or amounts of alkali needed to adjust the slurries to pH 12.5 were relatively high for all species because of weak acid groups in wood that dissociate at pH greater than 8. This explains the ability of wood to buffer highly alkaline adhesives. The pHs of slurries of two acidic melamine-urea-formaldehyde adhesives increased in the presence of wood, but the effect was less significant compared with the alkaline adhesives. Similarly, the "alkalinities" or amounts of acid required to adjust the slurries to pH 3 were relatively low. Aspen veneer samples had a greater effect on adhesive pH than spruce and Douglas-fir. These effects will help mitigate potentially adverse effects of strongly alkaline or acidic adhesives on wood adhesive bond strength
Environmental Impact of Manufacturing Softwood Lumber in Northeastern and North Central United States
Get PDFFinding the environmental impact of building materials is becoming increasingly more important because of public environmental awareness. Accurate and precise life-cycle inventory data on wood products are needed to meet this demand. This study examined softwood lumber manufacturing in the northeastern and north central US using life-cycle inventory methods. Material flow, energy type, and energy use were identified for these sawmills. A softwood log mass conversion of 42.1% to planed dry lumber was found. Values of 355 MJ of electricity and 2730 MJ of processed energy per cubic meter were determined for manufacturing planed dry softwood lumber burning mostly green wood residues onsite for energy. Biomass and fossil carbon dioxide production of 187 and 65.1 kg/m3, respectively, were estimated. Lowering energy consumption would be of great benefit to the mills, and thus society, in reducing the environmental burden, especially in sawing and drying
Influence of Acoustic Velocity, Density, and Knots on the Stiffness Grade Outturn of Radiata Pine Logs
Get PDFThe prediction of log-average lumber modulus of elasticity (MOE) from log measurements of acoustic velocity, green density, heartwood content, and branch and whorl variables was evaluated for green and kiln-dried boards of unpruned second and third logs of mature radiata pine. The use of principal component analysis showed there were strong associations between the log acoustic velocity and branch size variables, the number of branches and whorls and mean internode length, and the green density and heartwood content. These relationships were reflected in the regression models that showed good predictions of log-average green and kiln-dried board MOE from log acoustic velocity and green density or heartwood content with only a small contribution from branch and whorl variables
Effects of Sample Size on Characterization of Wood-Particle Length Distribution
Get PDFThe effects of sample size on fitting length distribution of wood particles used for manufacturing wood-based composites were investigated. A simulation study was conducted to evaluate the variations of the first four sample moments and the ability of the sample distributions to characterize the population represented by the original data. Results showed that a sample size of 2000 was deemed necessary to adequately represent distributions of wood particle length