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Time-dependent response of treated and untreated plywood to various modes of water exposure was studied. Treatments included 1.3-dimethylol-4.5-dihydroxyethyleneurea (DMDHEU) and phenol-formaldehyde (PF). The effect of thermal modification was also investigated. Water exposure regimes included: one-sided water spray, one-sided water soak, and high humidity – all for a duration of 192 h. Direct measurements of dimensional change were recorded, and digital image correlation (DIC) was used to continuously monitor two-dimensional swelling. Over 90% of thickness swell occurred during the first 24 h of liquid water exposure. Swelling was still progressing under 90% relative humidity exposure after 192 h. DMDHEU and PF were statistically equivalent and improved thickness swell by 64% and 60%, for water spray and water soak, respectively. Chemical treatment improved thickness swell by approximately 41% under high humidity. Thermal modification improved thickness swell by 36%, 28%, and 28% for water spray, water soak, and high humidity exposure after 192 h, respectively. DIC measurements during the first 3 h of exposure revealed the fastest rate of thickness swell occurred with one-sided water spray and the slowest rate during one-sided water soak. Overall, PF-treated plywood exhibited the best initial water resistance. After 24 h DMDHEU and PF were equally effective treatments. [ABSTRACT FROM AUTHOR]

Naturally durable wood species such as western juniper (Juniperus occidentalis) are a potential source of bio-based wood preservatives for the improvement of non-durable timber species. This research investigated the durability of southern yellow pine (Pinus sp.) and western juniper lumber or strandboard. Single layer panels were made with six different types of wood or wood treatments: southern yellow pine, mixed juniper sapwood and heartwood, sapwood, heartwood, sapwood strands impregnated with juniper oil prior to and after panel manufacturing. Panels were fabricated with 560 kg/m3 oven-dry density with 5% of PF resin and 0.5% of wax. Durability testing was performed with the brown rot fungi Gloeophyllum trabeum and Rhodonia placenta and the white rot fungus Trametes versicolor. Internal bond as a crucial parameter of OSB was measured. Tests revealed that juniper heartwood and juniper heartwood strandboards were highly decay resistant, and juniper oil pre- and postimpregnation strandboard manufacture imparted increased resistance to decay against one brown rot fungus, Gloeophyllum trabeum. Juniper strandboard manufactured from non-impregnated strands showed significantly higher internal bond than pine. These results suggest there is excellent potential for manufacturing highly decay-resistant OSB from juniper, especially from heartwood and that juniper oil can increase the durability of juniper sapwood strandboard. [ABSTRACT FROM AUTHOR]

This work investigated the feasibility of using western juniper (Juniperus occidentalis) as a material to manufacture oriented strandboard (OSB) panels. Four different material combinations of juniper sapwood, heartwood, and fibrous bark were compared with regular southern yellow pine (Pinus sp.) strands. The OSB panels were made at an oven-dry density of 560 kg/m3. One pine control panel was also made at a higher density of 650 kg/m3 with a 5% addition of phenol formaldehyde (PF) resin and a 0.5% addition of wax. The single-layer panels were formed with a hot press, and the physical and mechanical properties were tested according to the ASTM standard D1037 (2020). The testing indicated that western juniper is a potential material for manufacturing of OSB panels. The properties of the juniper panels were equivalent or slightly better than those of the southern yellow pine panels at the same density level, except for the modulus of elasticity (MOE). The lower density of the juniper OSB panels may have benefits in construction applications and can decrease transportation costs. [ABSTRACT FROM AUTHOR]

Wood structural panels are commonly subjected to short-term accelerated weathering (AW) procedures to determine relative moisture durability for quality control and product development purposes. The panel edges contribute heavily to moisture uptake since edges represent the least resistant pathway for moisture intrusion. In full-size panels, the edge area to total surface area ratio is small, and moisture intrusion is primarily limited to panel faces. When small specimens are used, such as those in AW procedures, the ratio of edge area to total surface area increases and moisture intrusion at the edges may dominate, which is referred to as the edge effect. The purpose of this study was to determine if physical and mechanical properties of oriented strand board (OSB) and plywood after AW are influenced by specimen size. Specimen width was varied while thickness and length remained constant to understand if edge effects were present in small specimens with different edge area to total surface area ratios. Three AW procedures were evaluated to determine if the effect of specimen size depends on weathering method. No clear effect of specimen size on physical and mechanical properties of either composite type was found. Differences in flexural properties between specimen widths were observed for unweathered OSB, but similar property retention between specimen widths after AW indicated the same trend as the unweathered control. Plywood results were influenced by natural defects, resulting in high variability and absence of statistically significant differences. Lateral nail resistance connection properties of both OSB and plywood were highly variable for all treatment groups and were unaffected by weathering. [ABSTRACT FROM AUTHOR]

The quality of wood composites is dependent on the bondlines' performance and their moisture resistance. The effect of moisture intrusion into bondlines is the focus of this study. The strain profile in the bondline during loading was investigated and the effects of weathering on the bondline were quantified by digital image correlation (DIC), while load deflection data were collected from lap-shear tests (LShTs). A total of 75 LShTs were evaluated including four different adhesive types with Douglas-fir wood, out of which 39 served as controls and 36 as substrates for weathering. The effect of weathering on failure load was not statistically significant. Only the bonded surface and adhesive type have significant effects on failure load, as well as the three-way interaction between the bonded surface, adhesive, and weathering, as revealed by three-way analysis of variance (ANOVA). The average effective shear moduli for the weathered samples were significantly lower than those for the control samples. [ABSTRACT FROM AUTHOR]

In the present study, fast-grown western hemlock (Tsuga heterophylla) was subjected to a thermal-hydro-mechanical (THM) treatment. Bond-line shear strength and durability were evaluated, and three parameters (substrate density, adhesive type and amount of adhesive spread) were investigated. To understand how THM processing affects bond performance, surface roughness and cell morphology of wood, before and after THM treatment, were observed. Adhesive penetration depths and patterns in untreated wood and THM-treated wood were also examined. In addition, Fourier transform infrared (FTIR) spectroscopy analysis of bond-line and microscopic observation of interphase region were conducted. Results revealed that polymeric diphenylmethane diisocyanate (PMDI) and polyurethane (PUR) had better bonding performance than phenol formaldehyde resin (PF). THM treatment improved bond durability, and THM plywood met the adhesive bond requirements of exterior plywood. THM treatment reduced surface roughness and porosity of wood. Adhesive penetration patterns were different in untreated wood and THM-treated wood and were affected by amount and type of adhesive. Pathways for adhesive flow into western hemlock were primarily tracheid lumens, ray cell lumens and the interconnecting pits. PF is the only adhesive that showed no evidence of flow via ray tissues or cell wall penetration. Since bond-line shear strength largely depends upon the weakest link across the laminas, ultimate strength or percent wood failure does not always depend merely on adhesive penetration. In addition, FTIR analysis showed different chemical reactions and bonding mechanisms, which provides a possible explanation of THM-caused changes in bonding performance at the molecular level. [ABSTRACT FROM AUTHOR]

Green building practices have created an opportunity for the forest products industry to become a leader in the creation of in- novative building products derived from renewable materials. In other industries, sandwich composites have proven to be efficient structures by meeting structural demands of traditional panel products while consuming less material. A prototype molded-core sandwich panel made of span-rated oriented strand board (OSB) facings and a bidirectional molded wood-strand core was produced. Critical mechanical properties were evaluated to determine the feasibility of this product for use in building applications. The goals of this study were to generate details on structural performance of the product, validate the design, and provide suggestions for future product development. Results indicate that this molded-core panel performs particularly well in flexure while connection properties had the largest scope for improvement. Sufficient performance was observed to validate the design, warranting production and testing of panels sized for end-use. Future product development should explore different connection systems, perform detailed engineering analyses of the mechanical properties necessary for complete structural design, and characterize physical properties of the panel. [ABSTRACT FROM AUTHOR]

Micro X-ray computed tomography (XCT) was used to analyze the 3D adhesive penetration behavior of different wood–adhesive bondlines. Three adhesives, a phenol formaldehyde (PF), a polymeric diphenylmethane diisocyanate (pMDI), and a hybrid polyvinyl acetate (PVA), all tagged with iodine for enhanced X-ray attenuation, were used to prepare single-bondline laminates in two softwoods, Douglas-fir and loblolly pine, and one hardwood, a hybrid polar. Adhesive penetration depth was measured with two separate calculations, and results were compared with 2D fluorescent micrographs. A total of 54 XCT scans were collected, representing six replicates of each treatment type; each replicate, however, consisted of approximately 1500 individual, cross-section slices stacked along the specimen length. As these adhesives were highly modified, the presented results do not indicate typical behavior for their broader adhesive classes. Still, clear penetration differences were observed between each adhesive type, and between wood species bonded with both the PF and pMDI adhesives. Furthermore, penetration results depended on the calculation method used. Two adhesive types with noticeably different resin distributions in the cured bondline, showed relatively similar penetration depths when calculated with a traditional effective penetration equation. However, when the same data was calculated with a weighted penetration calculation, which accounts for both adhesive area and depth, the results appeared to better represent the different distributions depicted in the photomicrographs and tomograms. Additionally, individual replicate comparisons showed variation due to specimen anatomy, not easily observed or interpreted from 2D images. Finally, 3D views of segmented 3D adhesive phases offered unique, in-situ views of the cured adhesive structures. In particular, voids formed by CO 2 bubbles generated during pMDI cure were clearly visible in penetrated columns of the solidified adhesive. [ABSTRACT FROM AUTHOR]

Compression creep experiments of Douglas-fir wood (Pseudotsuga menziesii) were performed at high temperature (150°C, 160°C, and 170°C) and under various conditions of steam pressure. The results established that environment conditions had a significant effect on compressive deformation, with the largest deformation obtained under saturated steam conditions. While the temperature significantly affected the compressive deformation of specimens under transient conditions, the temperature within the range studied had little effect on the compressive deformation in saturated steam. Furthermore, in specimens compressed under superheated and transient steam conditions, primary creep behavior was exhibited; while in specimens compressed under saturated steam conditions, creep deformation appeared to enter directly into secondary creep. Moreover, in saturated steam specimens very little creep was observed due to high initial deformation and little potential for additional cell wall buckling. The compressive creep measurements of Douglas-fir were compared with compressive creep of hybrid poplar (Populus deltoides×Populus trichocarpa). Due to lower initial density, and perhaps smaller microfiber angle and lower lignin content of tension wood, the compressive creep modulus of hybrid poplar was lower than Douglas-fir. Therefore, compressive deformation of Douglas-fir, at nearly all examined steam conditions and temperatures, was smaller than compressive deformation of hybrid poplar. [ABSTRACT FROM AUTHOR]

Compression creep experiments of hybrid poplar (Populus deltoides×Populus trichocarpa) were performed in a pressurized vessel equipped with a heated hydraulic press. The viscoelastic response at various stress levels (2-7 MPa), a temperature of 170°C and transient steam conditions was studied. Moisture content and oven-dry density of compressed specimens were determined. While some recovery of compression strain occurred, compression resulted in permanent deformation and increased wood density. The influence of stress level on the amount of set recovery of compressive deformation was evaluated after 24 h water soaking. Applied stress level had a significant effect on the compression deformation. The initial strain, as well as creep strain, varied depending on the applied stress level. The highest oven-dry density was obtained at a stress level of 6.9 MPa. Lower stress levels resulted in lower moisture content after the compression process, while the equilibrium moisture content of compressed specimens was not significantly affected by stress level. Set recovery increased from 20% to 65% with increased stress level from 1.7 MPa to 4.1 MPa, then decreased to 53% for specimens compressed at 6.9 MPa. Moisture content after the compression process significantly affected the set recovery. [ABSTRACT FROM AUTHOR]

The main objective of this study was to investigate the properties of polymer composites reinforced with grape cane fibers. The fibers were subjected to a sodium hydroxide (NaOH) treatment at two treatment concentrations to extract the fibers as well as fiber surface treatment. Panels were fabricated by hand lay-up and compression molding according to different fiber types, namely outer bark (OB) and whole (W) fibers. The whole fiber was a mixture of OB and inner bark (IB) fibers. Grape cane fibers were used as the reinforcement material for unsaturated polyester (UPE) resin panels. Acrylated epoxidized soybean oil (AESO) was used as a reactive diluent material with the UPE resin, and the results were compared with panels prepared with commercial styrene–UPE. There were inconsistent alkali treatment concentration effects on the mechanical properties and water absorption. However, panels fabricated with the whole bark fibers that have been treated with 1 wt % NaOH and had AESO–UPE resin resulted in the best tensile and flexural strength. [ABSTRACT FROM AUTHOR]

Abstract: Dielectric analysis (DEA) was conducted for continuous in-process monitoring of the curing of phenol formaldehyde (PF) adhesive. The influence of wood moisture content (MC) on the dielectric signal obtained in the PF adhesive bond was examined. The cure kinetics of the PF adhesive was evaluated at five different press temperatures, ranging between 120 and 200°C. The results showed that dielectric changes monitored by a LCR meter (impedance analyzer) and fringe-field sensor were related to the PF adhesives cure—which involves chemical reaction and water movement/diffusion from the adhesive bond line—but not related to the changes of the moisture in the wood. The rate of cure was strongly affected by the press temperature. The higher press temperatures induced a faster temperature rise in the PF adhesive bond, and thus accelerated the curing process. An nth-order kinetic equation was fit to the DEA degree of cure data to demonstrate the utility of DEA to characterize PF adhesive cure. [Copyright &y& Elsevier]

A mathematical model of the hot-pressing consolidation process for manufacturing a multi-layered oriented strand composite is developed and tested. Such a process model requires independent physical properties and user-specified structure for each layer of the mat. The model uses two-dimensional (slow variation is assumed in the third dimension) heat- and mass-transfer theory and a viscoelastic compression model. The through-the-thickness (vertical) density profile (VDP) was found to be highly dependent on the initial moisture content gradient, internal mat strand properties, and hydrothermal compressive response of the mat. The VDP predicted by the model showed good agreement with experimental results. The proposed mathematical model thus shows promise as a tool to analyze optimally design-oriented strand composites. [ABSTRACT FROM AUTHOR]

A novel wood-based composite has been developed for use in structural applications. The process was designed to utilize rapidly-grown, low density, wood species. Plantation grown radiata pine is particularly well suited to this process. This is a laminated composite, where the lamina may be comprised of various materials, some of which have been treated with the viscoelastic thermal compression (VTC) process. The VTC process increases the density of wood, without causing fractures in the cell wall, thus increasing strength and stiffness of the wood material. The process may be applied to veneer, sawn wood, or strand composites. The VTC lamina is then bonded to other lamina to produce the final product. The strength and stiffness of this VTC composite exceeds any wood-based composite that is currently on the market. For example, modulus of elasticity in bending of over 20 GPa is easily obtainable. [ABSTRACT FROM AUTHOR]

Surface energy of yellow-poplar wood from three wood treatment groups was studied using sessile-drop contact-angle measurements and the Chang acid–base model for surface energy calculation. Water, glycerol, formamide, ethylene glycol and α-bromonaphthalene were used as probe liquids. Wood treatments were control, hygro-thermal treatment and densification. Contact angle trends for densified and hygro-thermally treated wood were found to be the same. Total surface energy decreased with both hygro-thermal treatment and densification. [ABSTRACT FROM AUTHOR]

Bond performance of hygro-thermally compression densified wood was studied using hygro-thermally treated and control yellow-poplar wood (Liriodendron tulipifera). Opening mode double cantilever beam fracture testing and cyclic boiling were used to evaluate bond performance. Phenol–formaldehyde (PF) film and polymeric diphenylmethane diisocyanate (pMDI) adhesives were used to bond specimens for fracture testing. Fracture toughness of hygro-thermal samples bonded with PF film was significantly higher than control samples, while no difference was found for densified samples. Fracture toughness of densified samples bonded with pMDI was significantly higher than control samples, however no change was seen for hygro-thermal samples. Cyclic boiling reduced the fracture toughness of hygro-thermal fracture samples only, irrespective of adhesive type. [ABSTRACT FROM AUTHOR]

Viscoelastic thermal compression (VTC) is an excellent method for improving the physical properties of low density woods, but it has little effect on resistance to microbial degradation. The potential for improving durability through pre-impregnation with either phenol formaldehyde resin (PF) or tung oil was investigated in laboratory tests. Tung oil had little effect on decay resistance; while PF resins markedly improved durability against both white and brown rot fungi. The results suggest that resin pre-treatment was compatible with the VTC process and produced markedly more durable materials. [ABSTRACT FROM AUTHOR]

Unlike constant moisture effects on the behavior of composite materials, transient moisture effects are not well studied and known. Armstrong and Kingston have shown that the creep of wood under transient humidity levels could be greatly accelerated over that at any constant moisture content. Later this phenomenon was termed "mechano- sorptive". In this paper, the authors show that aramid fibers (Kevlar® 29, Kevlar® 49, and Kevlar® 149) and Kevlar® 49/epoxy composites exhibit mechano-sorptive phenomenon. Kevlar® composites were studied using both creep and dynamic mechanical analysis while undergoing desorption. Creep of single Kevlar® fibers was studied during relative humid ity conditions cycled between 5 % and 95 %. The results observed with Kevlar are consis tent with those reported for other natural polymeric materials. [ABSTRACT FROM PUBLISHER]

Spalted wood, wood colored by fungi, has been popular in woodcraft for centuries. Most spalted wood, however, is found in an advanced state of decay and cannot be utilized. This project describes the use of viscoelastic thermal compression (VTC) to investigate the potential increase in spalted woods' strength and stiffness, with the main objective of converting so-called "punky" wood into the top layer (veneer layer or "coating") on commercial flooring. Spalted Acer macrophyllum logs were cut into veneers of size 7 mm × 7.8 cm × 25 cm and were then VTC-treated at 150 °C and 50 psi for 11.5 min. Statistical analysis on the mixed linear models showed significant increases for both the density and hardness of spalted wood (p < 0.0001). Density and Brinell hardness increased by 84% and 209%, respectively. FTIR analysis revealed that the wood polymers present in spalted wood were more susceptible to degradation imposed by the heat of the VTC treatment compared to sound wood. Additionally, the color analysis of the wood specimens showed statistically significant changes in color after the VTC treatment (p < 0.0001), which turned the wood surface darker and redder. The use of the VTC technology to transform spalted wood into wood flooring is viable. However, when exposed to moisture, the VTC-treated spalted wood showed a high percentage of set recovery (78%), which was significantly different from the set recovery of the sound wood (71%, p = 0.004). Successful use of VTC-treated spalted wood for flooring will require addressing of the swelling issue, and additional studies are needed to fully characterize the anatomy of VTC-treated spalted wood. [ABSTRACT FROM AUTHOR]