Abstract

Experimental wood–plastic composites (WPCs) were made so that they matched the manufacturing process, dimensions, and water absorption of some commercial decking boards. WPC samples from selected formulations were divided into two identical groups. The first group was exposed in exterior conditions in Vancouver, British Columbia, and Hilo, Hawaii, at sun and shadow sites. Water absorption and biological activity were monitored by field inspection, density change measurement, and optical and scanning electron microscopy. The second group was used for soil block culture testing performed according to AWPA E10 (or ASTM D1413). Specimens were conditioned by immersion in water at room and elevated temperatures. Results of fungal decay activity are reported as specimen weight loss or corresponding density decrease. Observed density changes during field exposure and soil block culture testing are compared. Samples exposed to aggressive exterior conditions underwent decay, which was detected by microscopic inspection of board cross sections and calculated density decrease. Fruiting bodies of brown-rot decay fungi (Dacryopinax spathularia) were found on some sample surfaces during field inspections. The decay process of tested materials in the field seemed to require an initiation period dependent on exposure site. The shortest initiation time and the most aggressive environment for decay of WPC samples were found at the sunny site in Hilo. Laboratory soil block culture testing showed weight loss and density decrease of experimental WPCs to depend on conditioning. Correlations between laboratory test results and WPC performance in the field are described.

Abstract

The residual protective effect of sodium n-methyldithiocarbamate (NaMDC) fumigant was investigated in Douglas-fir timbers in a bridge in western Oregon using fungal colonization and levels of methylisothiocyanate (MITC; the primary fungitoxic breakdown product of NaMDC) as the measures of protection. MITC levels were above the presumed protective threshold 7 years after treatment and remained above that level in four of five timbers 12 years after treatment. These results differ from those found in round timbers and suggest that the combination of a protective-treated shell and the sawn surface resulted in a more prolonged protective period against renewed fungal attack. These results illustrate the benefits of NaMDC treatment on bridge timbers.

Abstract

This research was performed to evaluate the decay hazard for exterior aboveground wood in Korea. The decay hazard (Scheffer) index values were calculated for 56 locations in Korea using the 1972 to 2011 climate normal data available from the Korea Meteorological Administration, and the wood decay hazard maps were created on the basis of the determined values. Jeju Province, Korea's largest island lying in the Korea Strait, southwest of South Jeolla Province, has decay hazard ratings above 70, considered a severe decay hazard zone according to the generally accepted classifications. The index values of the other areas are in the range between 35 and 70, meaning that Korea could be considered a moderate decay zone. However, the annual Scheffer index values calculated from recent climate data tend to be higher than the average index values. The comparison of annual Scheffer index values showed that many moderate decay areas in Korea could be severe decay hazard areas due to directional or cyclical climate change. This suggests that proper wood protection is greatly needed and more critical in the future.

Abstract

Transparent and semitransparent coatings applied to wood products often fail due to photochemical degradation and colonization by black stain fungi. Longer-lasting coatings are needed to enhance the competitiveness of wood products used in appearance applications. We hypothesized that shell treatment with carbon-based wood preservatives combined with a protective precoat containing organic ultraviolet (UV) absorbers and hindered amine light stabilizers would control black stain fungi and provide enhanced coating service life. After 3 years of field exposure at Maple Ridge, British Columbia, and Saucier, Mississippi, samples were evaluated for degree of black stain, coating degradation, and substrate damage. Heartwood substrate, preservative treatment, and use of protective precoats were associated with better stain resistance and enhanced coating performance. Use of preservative treatments and UV protective precoats is recommended to enhance the service life of high-quality transparent and semitransparent finishes. However, further work is needed to enhance the performance of transparent and semitransparent coatings to meet consumer demands for low maintenance.

Abstract

Microwave wood bending involves softening wood using microwave energy and then bending it into a required shape. An experimental framework was developed that included two sets of experiments: microwave mechanical property experiments (MMPE) and microwave wood-bending experiments (MWBE).

This article reports on an investigation into the effect of the salient wood-bending variables on important mechanical and bending characteristics of Eucalyptus regnans wood, using a full factorial experimental framework and associated statistical analysis. Variables investigated were moisture content in the range of 18 to 20 percent and above 35 percent; wood temperature in the ranges of 80°C to 85°C, 100°C to 105°C, and 120°C to 125°C; MMPE for three wood strain rates of 0.1, 0.2, and 0.6 mm/s; and MWBE for three strain rates of 13°/s, 27°/s, and 81°/s.

This article reports on two objectives: (1) the development of a full factorial experimental design framework for wood-bending research, and (2) the application of this framework to efficiently determine salient mechanical properties of E. regnans during microwave bending and to determine the bending parameters required for optimum microwave bending of this species. Bending strains for compression parallel-to-grain, shear parallel-to-grain, and tension parallel-to-grain were investigated.

The study revealed the following optimum microwave bending variables for E. regnans: moisture content above 70 percent, temperature in the range of 100°C to 105°C, and strain rates in the region of 0.1 mm/s or 13°/s.

The study authenticated an optimum set of bending variables for the microwave heating of E. regnans that enabled minimum wood failure during bending operation.

Abstract

The production of eucalyptus for the cellulose and paper industry is based on the cultivation of clones, which are obtained by crossing species with desirable characteristics. However, clones that were considered to have great potential have presented serious problems because of permanent bending and breakage, which are caused mainly by wind forces during the early years of growth. Wave propagation methods have shown great potential in applications related to predicting the stiffness of logs and lumber. Based on the premise that the stiffness of the stem is a major contributor to a tree's resistance to the wind, the objective of the present study was to determine whether an ultrasound wave propagation test performed directly on trees would have the sensitivity within a sample group to differentiate between clones and whether this differentiation would be consistent with the differences in stiffness between them. The stem was used to evaluate the stiffness of clones rather than logs, pieces of a structural size, or specimens. A cantilever static scheme and the application of a load near the top of the stem were intended to simulate field conditions. A total of 189 trees were tested from 21 different clones. To differentiate the clones, the ultrasound wave propagation velocity was obtained directly from the trees. The velocity differences among the trees were consistent with the results obtained using the stem stiffness of the same trees.

Abstract

An air-drying process was designed to avoid material decomposition and eliminate the high cost involved in other drying and storage methods. This process, which involved no chipping of biomass at the harvest site, was tested at two study sites in Escanaba, Upper Peninsula, Michigan, from June to November 2011. The primary objective of this study was to evaluate the effect of air-drying on biomass moisture content (MC) and higher heating value (HHV) over field storage. In addition the impacts of different positions within a pile, biomass pile sizes, and weather conditions on biomass moisture change were also tested. Results showed that biomass MCs were significantly reduced during the 5-month field storage period. In addition, the biomass MCs at different positions within a biomass pile were found to be statistically uniform. Results further suggested that making a biomass pile smaller is an appropriate way to store woody biomass when it is scheduled for short-term use, while larger piles should be considered as an option for long-term storage. Biomass HHVs were found to be stable during the 5-month storage period. These results indicate that field piling of unprocessed biomass is a reliable solution for year-round biomass supply without incurring additional costs. Regression analysis also showed that field-stored biomass MC can be significantly impacted by air humidity, while the effect of air temperature and cumulative precipitation on biomass MC was minor.

Abstract

After conducting mechanical tests, the moisture content (MC) of the test specimens is determined. If the MC is not 12 percent, the standard procedure is to adjust the test value to equal those at 12 percent MC. With new treatments such as high-temperature heat treating, however, 12 percent MC may not be an appropriate value for adjustment. Tests were conducted using three species (southern pine [Pinus taeda], red oak [Quercus sp.], and sweetgum [Liquidambar styraciflua]), three temperatures (100°C, 150°C, and 200°C), and three conditioning environments (conditioning chamber, outside air, and enclosed over water). The results indicated that the higher the treatment temperature, the more difficult it was to reach 12 percent MC. For example, the MC of the samples treated at 200°C in the conditioning chamber was 7 or 8 percent, whereas the MC of the controls was 13 percent. These results imply that adjusting test values to 12 percent MC would be inappropriate if all specimens were conditioned in the same environment.

Abstract

The available wood supply in Uruguay comprises trees that grow so fast in intensively managed plantations that they reach saw timber size in 25 years or fewer. Trees harvested at this age contain high proportions of juvenile wood that may lead to lumber low in stiffness and strength. A project was conducted to characterize fast-growing wood, determine engineering properties, and assign visual structural grades of lumber. The present study evaluated properties of 15- and 25-year-old loblolly (Pinus taeda L.) and slash (Pinus elliottii Eng.) pine to better understand the current available locally produced wood material. A total of 175 stump bolts from trees from two commercial plantations provided inner and outer small clear specimens for property evaluation. Specific gravity, bending, compression parallel to grain and perpendicular to grain, and shear tests were conducted. Most properties significantly increased radially away from the pith. The outer wood appears to be denser, stiffer, and stronger than the inner wood in both plantations. Wood from 15-year-old San José trees showed significantly lower properties than 25-year-old Paysandú trees, and had considerably inferior properties compared with values listed in the Wood Handbook (US Department of Agriculture 1999). Our results on 25-year-old Paysandú small clear specimens showed properties similar to those of previous studies on small clear and structural size pieces. Therefore, it can be expected that lumber from 25-year-old Paysandú trees will eventually comply with required properties for structural use. A second on-going phase of this study addressing structural size specimens will help to establish more definite conclusions.

Abstract

Soy flour adhesives using a polyamidoamine-epichlorohydrin (PAE) polymeric coreactant are used increasingly as wood adhesives for interior products. Although these adhesives give good performance, higher bond strength under wet conditions is desirable. Wet strength is important for accelerated tests involving the internal forces generated by the swelling of wood and plasticization of the adhesive with increasing humidity.

Soy proteins are globular due to their hydrophobicity; thus, it was expected that adding modifiers to open the protein structure should improve protein–protein and protein–wood interactions to help withstand both internal and external forces applied to the bond. Because modifiers have been shown to improve the performance of soy protein isolate adhesives, use of these modifiers has been examined as a way to improve soy flour adhesives. Protein-disrupting chaotropic agents (urea, guanidine hydrochloride, and dicyandiamide), surfactants (sodium dodecyl sulfate or cetyltrimethylammonium bromide), and the cosolvent propylene glycol were all expected to provide increased protein–protein and protein–PAE interactions. Improved interactions would make the soy flour adhesives durable enough to better pass wet bond strength tests specified for most interior bonded wood products. However, no substantial improvement was seen in cured wood bond strengths in wet conditions for soy flour adhesives by adding any of these modifiers with or without PAE polymer addition. These results led to a proposal that carbohydrates, about 45 percent by weight of soy flour, are interfering with obtaining greater adhesive bond strengths from the protein portion of the flour.