Scott Leavengood

Rubberwood (Hevea brasiliensis Muell. Arg) is underutilized in most developing countries but has potential to be a solution to the shortage of wood for pulp, paper and wood composite products at the end of its production cycle. Determining and understanding its fibre properties (fibre dimensions and morphology) is key in its utilization for pulp and paper as well as composites. This study assessed the effect of age on the fibre properties of rubberwood. Samples of wood at four ages (10, 15, 20 and 25 years) were obtained at both the axial (base and top of merchantable length) and radial direction (innerwood, middlewood and outerwood). Slivers were obtained from the samples and macerated to provide individual fibres for optical measurement. Fibre dimensions at the four ages were measured, and their morphology was determined. Fibre properties and morphology were significantly affected by age at p = 0.05. Average fibre length was 1.47 ± 0.12 mm, with non-constant variation observed across the different ages, and from pith to bark. Average lumen width was 16.87 µm, and fibre diameter ranged from 25.02 µm to 27.23 µm. The fibre properties of rubberwood potentially make it suitable for pulp and paper production as well as wood composite boards.

Recent developments in factory-grown foods suggest that factory-grown wood (FGW) may be on the horizon. In fact, recent work at Massachusetts Institute of Technology introduces tunable plant-based materials, an early indicator of what may evolve into a new source of raw material for forest sector companies, and others. Industry and academia would be wise to monitor developments in this field as they may present significant opportunities and/or adjustments for both. We explore the state-of-the-art in this budding area of science and contemplate implications of successfully growing wood or other lignocellulosic materials in factories. Given a changing climate and focus on carbon emissions, the pressure to drastically reduce CO2 production will continue climb. Could reduction of their footprint via FGW be an important part of this equation for forest sector companies, going beyond the need to “make every tree count”? In other words, might FGW present an environmental and climate protection breakthrough? Or might it simply trade forest-based environmental impacts for others? What other consequences does FGW promise for companies? And, what might it mean for wood science programs, critical suppliers of research & development and skilled employees for the industry? We explore each of these questions and contemplate potential actions and outcomes.

Wood exposed in exterior applications degrades and changes color due to weathering and fungal growth. Wood coatings can reduce the effects of weathering by reducing the damaging effects of ultraviolet light, reducing water absorption, and slowing fungal growth on the surface. Coating performance depends on the blend of resins, oils, and pigments and varies considerably among different wood species and conditions. Specific information describing expected service for different wood species and exposure conditions is not commonly available; certain combinations may work well in one climate or on one timber species, but underperform elsewhere. This study compared the performance of three industrial wood coatings on two wood species for two temperate climates under natural weathering conditions. Most of the coatings/species combinations lost their protective properties within 12 to 15 months; however, fungal growth was more prevalent at the wetter site than at the drier site for several combinations. Film-forming coatings often peeled and cracked, while penetrating coatings weathered and changed color relatively uniformly during the study. While no coating was completely effective, the results illustrate the benefits of using coatings that promote the development of natural, uniform-patinaed wood surfaces. The findings also guide coating maintenance programs for mass timber structures exposed to natural weathering conditions.

Dimensional stability of wood-based composites with changing moisture content remains an important challenge in the industry for many applications. Wood identification technologies have shown significant promise to improve dimensional stability. The main objective of this research project was to study the effectiveness of impregnation and heat treatments on wood composites when exposed to selected moisture environments. Moisture exposure conditions included one-sided water spray, one-sided liquid water contact, constant high RH, and cyclic exposure to high and low RH. Commercial moisture-resistant medium-density fiberboard (MDF) and birch plywood panels, as well as laboratory manufactured birch plywood panels, were modified by impregnation with phenol-formaldehyde (PF) resin, 1,3-dimethylol-4,5-dihydroxyethylenurea (DMDHEU) resin, or subjected to heat treatment at 205^oC for 2 h to improve dimensional stability. All treatments improved moisture resistance. Plywood impregnated with PF or DMDHEU resin showed the lowest thickness swelling values, with maximum values not higher than 5% after 192 h of exposure. Heat-treated MDF and heat-treated plywood samples resulted in 11% and 6% thickness swell after water spray exposure, respectively. The heat-treated plywood resulted in lower linear expansion (LE) than untreated plywood, with an average reduction of 54%; whereas the heat-treated MDF material did not show improvement of LE relative to control MDF samples.

Understanding of wood quality of hybrid poplar is critically important for manufacturers who want to know the suitability of the wood for specific products. To this end, lumber was milled from the merchantable stem of four hybrid poplar clones ages 10-11 yr., grown at single site near Boardman, OR. The vertical and radial position in the stem were recorded for each board and the boards were kiln dried, surfaced, and samples from each board tested to determine specific gravity (SG), dimensional stability, hardness, screw withdrawal, and bending strength and stiffness (modulus of rupture [MOR] and modulus of elasticity [MOE], respectively) from small clear specimens. Results show differences in wood properties relative to vertical and radial position in the stem. SG, hardness, screw withdrawal, and bending properties of lumber samples generally increased with height in tree. Tangential hardness, SG, and MOR varied significantly between different sides of the trees corresponding to predominant wind in the area. Boards milled from the center of the stem had lower MOE and MOR than boards milled from nearer the bark. The results of this study may be used to target specific stem locations for different end uses.

Wood used in exposed exterior applications degrades and changes color due to weathering. Expanded use of mass timber is resulting in architects increasingly designing structures with wood in exterior exposure. Coatings can reduce the effects of weathering and prolong the visual characteristics of wood. However, coating performance depends on a variety of factors including the blend of resins, oils, pigments, and binders. Coating manufacturers often claim superior performance for products, but data directly comparing different coatings on different species is rarely publicly available. Premature coating failure increases long-term building maintenance expense while potentially enhancing biological degradation and reducing service life. This study compares the performance of 12 exterior wood coatings on 5 wood species. Performance was evaluated according to changes in the components in the International Commission on Illumination (CIE) L*a*b* color space of images taken at 6-month intervals over 18 months of the wood samples. The analysis was performed using Welch’s ANOVA, Games-Howell pairwise comparisons tests, and a clustering procedure using distances between each pair of groups means for the 18 months ΔL*, Δa*, Δb* values. Most of the coatings lost their protective effects within 1 year of exposure due to combinations of biological and ultraviolet radiation (UV) degradation illustrating the difficulty of protecting timber in exterior exposures. This study provides a guide for users wishing to specify coatings for exposed wood in mass timber structures.

An optical method based on digital image correlation was used to investigate the impact of four decorative plywood manufacturing factors (core type, veneer type, adhesive type and lathe check orientation) on face veneer checking. The four core types were: combination core, medium density fibreboard, particleboard, and veneer core. The four veneer types were: peeled 0.604 mm, peeled 0.706 mm, sliced 0.508 mm, and sliced 0.564 mm. Both loose-side out and tight-side out lathe check orientations were used. The adhesive systems were urea–formaldehyde, polyvinyl acetate, and soy-protein based. 96 treatment combinations with 8 replicates were tested. All specimens were exposed to harsh but realistic drying conditions (approximately 30°C and 26% relative humidity) for 4 h during inspection. Checks were detected on 428 out of a total of 765 specimens (56%). The estimated mean check densities (area of checking per unit area) indicated some unfavourable factor combinations. All factors had some degree of interaction with one another and check development could not be attributed to a single factor examined in this study. The data were fit to a generalized linear mixed model based on Tweedie’s compound Poisson distribution. Confidence intervals were calculated via bootstrapping. The check density estimates produced by this model can be used to cautiously guide manufacturers as they decide on panel components. The broader use of the model is to highlight the complexity of the problem and guide future research in this area.

The properties of several modified wood products were evaluated using North American standards to provide comparative data for architects seeking to use these materials. In general, modified wood products had lower moisture uptakes and less shrinkage than unmodified products. Acetylated materials were highly resistant to fungal decay, whereas thermally modified and furfurylated materials were classified as decay resistant. All materials were susceptible to mold, although the nonacetylated moisture-resistant medium-density fiberboard was most susceptible. Thermally modified and furfurylated materials were similar in mold susceptibility to untreated radiata pine sapwood, whereas acetylated materials appeared to be more mold resistant.

Western juniper (Juniperus occidentalis) is a conifer that is native to Oregon, California, Washington, Nevada, and Idaho. Juniper is highly decay resistant and, therefore, is a popular choice for fence posts and landscape timbers. Forest management practices over the past 100 yr have resulted in an immense population increase in western juniper stands, transforming the grasslands/sagebrush biome into juniper forests. Landowners have been encouraged to cut back western juniper to restore grassland habitat, but there is no major market associated with juniper lumber. This study assessed the mechanical properties of western juniper to develop its design values for inclusion in the National Design Specification. Small clear samples were prepared from juniper harvested from three locations in eastern Oregon, one location in northeast California, and one location in southwest Idaho according to ASTM D143 for compression, bending, and shear. Average strength values were calculated and compared with similar wood species. Most properties were similar to those of other species, but modulus of elasticity was significantly lower. Compressive properties of western juniper also differed, with compression parallel-to-grain being lower and compression perpendicular-to-grain being relatively higher. Differences between species might be attributed to cell wall structure and distribution of lignin in the cells. Design values for western juniper were calculated using the strength values to establish allowable properties for visually graded lumber.