Abstract
Growing international trade in wood pellets is one response to regional efforts to mitigate the global problem of climate change. With this growing use of wood energy, there is increased scrutiny of the associated environmental impacts and concern over possible unintended consequences (e.g., nonrenewable energy inputs) that may detract from the carbon savings provided by such renewable energy sources. The focus of this article is to present an accounting system for the embodied fossil fuels in wood energy systems. This system is based on life-cycle assessment methodology and could accommodate fairly the variability in fossil fuel inputs for various bioenergy systems. Such a system could be incorporated into biofuel subsidies or carbon taxation policies. We use three scenarios as examples to illustrate (1) that wood-to-energy systems entail the use of fossil fuels and that the amount of this “embodied fossil carbon” varies with the processing inputs and transportation required and (2) that carbon tax/biofuel subsidies can be adjusted to accommodate variations in embodied fossil carbon. The growth in life-cycle databases and the advent of environmental product declarations make embodied fossil fuel calculations such as those presented here an increasingly practical component of biofuels policy development.
Abstract
Because of the greater demand in using woody biomass for bioenergy and bio-based products, feedstock supply chain optimization becomes more important to decrease supply chain logistics costs. As a primary component in the biomass feedstock supply chain, the storage of harvested woody biomass can directly affect transportation cost, biomass quality, and combustion efficiency. An improved operations system structured with linear programming was developed for minimizing the total cost of woody biomass preprocessing, storage, and transportation. The improved operations system was applied in a simulated case study for a power plant in Michigan. In addition, a simulated second feedstock end user was added to the operations system to further test the model. The results showed that the improved operations system could lower supply chain logistics costs, improve feedstock quality, and simultaneously meet the feedstock end user's demand. The sensitivity analysis indicated that the additional profit from selling higher-quality feedstock could offset the increased transportation cost for up to 171 miles. On average, every 1 percent decrease in biomass moisture content can result in a decrease of $760.68 in total cost and a reduction of 52.1 green tons of delivered biomass to satisfy the end user's demands. The operation details suggested by the improved operations system can be used as a guideline of real operations to achieve the lowest possible operations cost. The additional profit return from selling higher-quality feedstock needs to be quantified for various conversion and upgrading options besides direct combustion in the future.
Abstract
Contamination of wooden framing structures with semivolatile organic chemicals is a common occurrence from the spillage of chemicals, such as impregnation with fuel oil hydrocarbons during floods. Little information is available to understand the penetration of fuel oil hydrocarbons into wood under ambient conditions. To imitate flood and storage scenarios, the sorption of n-hexadecane (representing fuel oil hydrocarbons) and water by southern yellow pine was studied using gravimetric techniques at ambient temperature and pressure. The sorption curves obtained had three distinct regions, reflecting three different sorption phases. Lower sorption coefficients were obtained for nonpolar n-hexadecane than for water, leading to n-hexadecane maximum mass uptake values being half those of water. Lower penetration values were obtained for epoxy-coated wood compared with uncoated wood, apparently because of the inaccessibility of diffusion paths along the wood lateral surface and slower air removal from tracheids. Two models were introduced to fit the observed sorption curves into a single algebraic equation, a diffusion (Fickian) model and an empirical (non-Fickian) equation. Effective diffusion coefficients were determined under the Fickian model, resulting in ca. 10−7 m2/s, 10−8 m2/s, and 10−10 to 10−11 m2/s diffusion rates for sorption in Phases 1, 2, and 3, respectively. The proposed non-Fickian model was based on first-order kinetic constants for the second sorption phase and fit the experimental data throughout all three phases. The two models were shown to corroborate each other by demonstrating that the effective surface areas of wood blocks calculated using both models' parameters were consistent with the corresponding expected physical values.
Abstract
The heat capacity of panels used for house sheathing is an important property that allows the hygrothermal modeling of thermal mass and the calculation of heating and cooling rates of certain types of walls. To our knowledge, this article presents the first data in over four decades for the measurement of heat capacity across a range of moisture content values. Although some estimates of panel heat capacity exist, few, if any, have been reported for mills across North America and across a range of moisture contents. The data clearly show the dependence of heat capacity on moisture content. They also show that solid wood and panel heat capacity values are similar at low moisture contents but diverge as moisture content increases. The variation in heat capacity with moisture content is large enough so that it should be considered when determining hygrothermal efficiency in walls containing plywood or oriented strand board or when developing hygrothermal models.
Abstract
The hot-pressing process is a vital step in the manufacture of wood-based composites and directly affects the properties and quality of the final products. During hot pressing, the heat and mass transfer process interact with each other, coupling with the mechanical deformation process of wood-based composites under the high-temperature interaction. In addition, the curing of resin, although governed by the laws of chemical reactions, can result in the release or absorption of heat and water, which may, in turn, affect the heat and mass transfer process. Realizing its complex and coupling nature, many scientists have conducted long-term, multisided and multilevel studies to better understand hot pressing. This work reviews the development of wood composite hot pressing, including the heating methods of hot pressing, the mechanism of heat and mass transfer, the hot-pressing models, and the experimental testing of the internal environment. The shortage of current studies and potential directions for future research are also discussed.
Abstract
Five 40-year-old Pinus taeda trees growing in Tochigi, Japan, were used to evaluate juvenile wood (JW) and mature wood (MW) properties and the bending properties of lumber. The boundary between JW and MW existed from the 14th to the 19th ring from pith in the sample trees. There were obvious differences in wood properties between the JW and MW: the MW had higher values in the latewood percentage and basic density and lower values in the microfibril angle. The microfibril angle and the air-dry density were closely related to the bending properties of the JW lumber and the MW lumber, respectively.
Abstract
The challenges of utilizing Eucalyptus grandis thinnings prompted a study into its anatomical properties with the aim of identifying its potential based on the within-tree axial and tree-age variation. Fiber length, fiber diameter, vessel length, vessel diameter, vessel average, ray height, and ray frequency at 3, 6, 9, and 12 years were studied. Axial sample portions at 25, 50, and 75 percent of tree height were collected from western Uganda and prepared for maceration, microtomy, and microscopy. Analysis of variance and Tukey's test were used to obtain axial and tree-age variation. Fiber length (819 to 1,077 μm) decreased axially in higher tree ages of 6, 9, and 12 years and increased with tree age. Fiber diameter (10 to 13.4 μm) varied inconsistently axially and decreased with tree age. Vessel length had no consistent axial pattern but decreased with tree age (338 to 548 μm). Vessel diameter showed higher values at 75 percent and increased with tree age (93 to 138 μm). Vessel average did not vary axially but decreased with tree age (8 to 11 vessels per mm2). Ray height did not vary axially but increased with tree age (107 to 278 μm). Ray frequency decreased with tree age (8 to 10 rays per mm2). E. grandis trees at the ages of 3, 6, 9, and 12 years have anatomical properties suitable for production of strong pulps although with a modest proportion of fines. Comparative research on cloned E. grandis varieties and their implied industrial potential would be appropriate to improve utilization of this fast-growing tree species.
Abstract
The aim of this study was to investigate the anisotropic characteristics of Brinell hardness for six species (softwood, Chinese fir [Cunninghamia lanceolata (Lamb.) Hook.], Red pine [Pinus koraiensis Sieb. et Zucc.], Mongolian scotch pine [Pinus sylvestris L. var. mongolica Litv.]; hardwood, Manchurian walnut [Juglans mandshurica Maxim.], Asian white birch [Betula platyphylla Suk.], Mongolian oak [Quercus mongolica Fisch. et Turcz.]) with the equilibrium moisture content (EMC) obtained at four relative humidity (RH) levels (20°C; 50%, 65%, 85%, and 95% RH). The results showed that the cross section of specimens presented higher Brinell hardness and lower elastic recovery than those tested on radial and tangential surfaces. Ovendried density was significantly positively correlated with Brinell hardness. With the exception of softwood on a tangential surface (r = 0.02), there was a statistically significant positive correlation of elastic recovery against ovendried density (at the 0.01 level). We found that a general increase in EMC significantly lowered the Brinell hardness for six species, irrespective of grain orientation. The decreased extent of relative Brinell hardness (HB/HB0) was highest for cross section samples, compared with radial and tangential surfaces. For three softwood species, the decreased extent of HB/HB0 on the radial surface was higher than that on the tangential surface, whereas the opposite relationship was found in three hardwood species. The results indicated that rays were probably the main factor controlling transverse anisotropy in hardwood, while the interaction of earlywood and latewood was more important for softwood. In addition, elastic recovery anisotropy was probably owing to different failure behavior in three directions, and it was difficult to establish a direct influence of EMC on elastic recovery.
Abstract
Determining the moisture content of wood during its drying process is important for the quality control of lumber. This study investigated the potential for using stress wave velocity to estimate moisture content in boxed-heart lumber from Japanese cedar (Cryptomeria japonica D. Don) and examined a methodology using Monte Carlo simulation for applying estimated moisture content to quality control. Lumber was subjected to natural drying for about half a year, from the green wood condition to near the fiber saturation point, during which time stress wave velocity and moisture content were measured about seven times. Stress wave velocity was confirmed to increase with decreasing moisture content, even for lumber whose cross-sectional dimensions were comparatively large. The relation between stress wave velocity and moisture content was expressible by a regression line over a range of moisture content above the fiber saturation point. The database for the relation between stress wave velocity and moisture content was further divided into three groups based on apparent density, and the same analysis was conducted. Estimation precision was found to improve over the entire moisture content range when analyzed within each individual group compared with analysis values obtained when ungrouped. Finally, application of Monte Carlo simulation to the moisture content estimations was able to account statistically for the variation in the relation between stress wave velocity and moisture content. This method was found to be effective in reducing estimation error for quality control purposes.
Abstract
The aim of this study was to investigate the application of microwave and steam injection drying on CO2 laser–incised teak (Tectona grandis) and mahogany (Swietenia mahagoni) lumber. The specimens were teak and mahogany lumber with dimensions of 60 by 120 by 600 mm. Three incising densities, 0, 1,250, and 2,500 holes per m2, were applied to the drying specimens. The drying process was carried out by a combination of microwave and steam injection drying. Microwave irradiation had a power of 3 kW at a frequency of 2.45 GHz, while steam injection drying was done by injecting superheated steam at 105°C to 110°C through a perforated plate at 110°C to 120°C. Drying rate, moisture content (MC) distribution, and checks were observed to evaluate the quality of the drying process. The results indicate that microwave heating and steam injection drying could successfully dry incised teak and mahogany lumber. The highest drying rate was achieved in the specimens with an incising density of 2,500 holes per m2. Interestingly, reducing the MC of teak from 46 to 20 percent required only 20 hours, while lowering the MC of mahogany from 60 to 20 percent took only 24 hours, without the formation of surface and internal checks. Laser incising, microwave heating, and the setting temperature of steam injection drying contributed considerably in creating a more uniform moisture distribution in teak and mahogany lumber, which significantly reduced surface and internal check formation.
Abstract
The potential for limiting fungal attack on red alder (Alnus rubra Bong.) pallet stock was evaluated in a small-scale field test. Alder is extremely susceptible to biological attack, as evidenced by the nearly complete colonization of nontreated materials within 18 days after cutting. Pallet stock was either dipped or sprayed with 11 different candidate fungicides. Dipping tended to produce better protection than spraying, reflecting the opportunity for greater uptake during the dipping process. Most treatments provided protection for 11 days when applied by dipping, while only four treatments were able to provide protection for the full 30-day test period. The results suggest that chemical protection of alder is possible, but the protective period is much shorter than that found with other wood species.
Abstract
Wheat straw–polypropylene (PP) composites were formed by mixing compression molding to evaluate the susceptibility to mold fungi colonization. The surface morphology, water absorption, Fourier transform infrared spectroscopy (FT-IR), and color variation of the wheat straw–PP composites were investigated before and after colonization with five kinds of mold fungi (after 1, 2, 3, and 4 wk). Macromorphologic and micromorphologic observations indicated fungal colonization was not obvious during the first week, and the wheat straw was perfectly encapsulated in the PP matrix. The original cracks became small holes when the outer wheat straw at the top surface was degraded after fungal colonization for 2 weeks. Consequently, the inner wheat straw was exposed to the fungal environment, and fungal colonization increased. Similar change trends were obtained through FT-IR spectra and color-change analyses. Some characteristic peak ratios in the FT-IR spectra were calculated to investigate the relative degradation rate. Results showed that the fungi used in this study preferentially degraded hemicellulose, followed by lignin, and then cellulose. The carbonyl and lignin indices were used to illustrate the loss in wheat straw mass during the process of colonization. The carbonyl index showed good correlation with the color change. A similar conclusion was obtained for the lignin index. The correlation analyses suggest color change has a close relationship to the process of degradation in wheat straw.
Abstract
Timber from plantation forest mostly contains sapwood, and the heartwood part has a lot of juvenile wood, which has low resistance to attack by subterranean termites (Coptotermes curvignathus). Wood smoke created through pyrolysis contains numerous polycyclic aromatic hydrocarbons that could prevent termite attack. Three-layer glued laminated lumber (glulam) was created using either the same wood species (mangium [Acacia mangium], manii [Maesopsis eminii], or sengon [Falcataria moluccana]) for all layers or a combination of mangium as the face and back layers and a core layer of manii or sengon. Glulam samples were exposed to smoke from mangium wood for 15 days, preserved with imidacloprid, or left untreated. All glulams were tested against subterranean termites according to the Indonesian standard. Gas chromatography revealed that smoke from mangium predominantly contained acetic acid, cyclobutanol, and phenolic compounds. Smoked glulam was more resistant to subterranean termite attack than untreated glulam, but less resistant than the imidacloprid-preserved glulam. On the basis of the resistance classification in an Indonesian standard, untreated glulam belonged to the moderate (class III) to very poor (class V) resistance classes with an average of 4.4, and smoked glulam ranked as moderate to poor (class IV) resistance with an average of 3.2. Imidacloprid-preserved glulam belonged to the very resistant (class I) to resistant (class II) classes with an average of 1.8, corresponding to resistance to subterranean termite attack.
Abstract
In this study, there were two kinds of recycled polypropylene (RPP) packaging bags, RPP disposable packaging bags (RPP-DB) and RPP woven bags (RPP-WB), used as matrix reinforced with wheat straw fiber (WSF). The aim of this study was to investigate the relative degradation behavior of WSF/RPP composites with two RPP matrices under weathering conditions. The RPP packaging bags were blended with WSF by a two-roll mill mixer and then molded by a compression molding machine. The effects of accelerated weathering on the surface morphology, surface color, surface chemistry, thermal properties, and mechanical properties were evaluated after distinct periods; the total time of exposure of the composites in a QUV-accelerated weathering tester was 1,200 hours. The weathering degradation process of WS/RPP-DB was gradual from surface to interior, whereas the internal collapse aggravated the performance reduction of WS/RPP-WB. The weathering resulted in significant discoloration. The photobleaching of WS/RPP-DB was faster than of WS/RPP-WB. The Fourier-transform infrared spectrum suggested that the color change was closely related to the formation of carbonyl groups and degradation of lignin. After weathering, the thermal properties of WS/RPP-DB and WS/RPP-WB were both decreased. The flexural strength and modulus of WS/RPP strongly decreased with exposure time and was related to the surface crack of composites. The utilization of RPP packaging bags as matrix could be a good candidate of wood–plastic composites for applications in the future.
Abstract
The export changes of primary forest products in the United States and China from 2005 through 2012 were compared, and a constant market share model was applied to analyze the impact factors on the export variations of the two countries. The results showed that the decline of import scale and structural changes of the target markets had a negative impact on the wood products export of the two countries. The export variations of primary forest products in the two countries were significantly different. While a small increase in the export of primary forest products was demonstrated in the United States, China's export increased significantly, especially to the major export markets. The change in competitiveness of forest products exports during this time period differed in these two countries. The competitiveness of forest products from the United States remained stable with slight variation; however, the forest products exported by China showed a strong increasing competitive trend.