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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]

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]

Densification techniques, combined with other treatment processes, helping additionally to improve wood properties, play an important role in wood modification. An innovative example of this combination with other techniques is the viscoelastic thermal compression (VTC) process. In this study, material of poplar wood from fast growing short rotation plantation (SRP), modified by VTC process, was used for investigation and results were compared with non-modified native wood of plantation grown poplar. Selected physical and mechanical properties, i.e., density, equilibrium moisture content (EMC), and modulus of elasticity (MOE) were investigated. The material, used for this investigation, was obtained from plantation grown poplar clone Max-4 (Populus nigra x Populus maximowiczii) from the Czech Republic. Results show that compression and heat treatment of the viscoelastic thermal compression process lead to significant changes in physical and mechanical properties of the treated material. The density of material depends on the degree of densification and has a crucial effect on properties. The goal of this study was to examine the improvement of properties of SRP poplar clone after applying the VTC densification process. Property improvement of plantation grown poplar wood has a huge potential for future use of this low-cost and fast-growing material, which would save high value materials for special uses. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental research performed with native hornbeam and Robinia stem - and branch wood of forest origin as well as property - modified wood from poplar of forest and plantation origin. Results show higher density and strength properties of different branch assortments, enabling native wood material application in special higher utilization demands. In the case of lower stem wood properties of forest or fast-growing plantation poplar (low density, strength, moisture related behaviour, durability), quality improvement due to wood impregnation shows amazing modified new properties, making possible utilizations even under highe rmoisture conditions or strength as well as hardness demands. First applications in flooring material or moist-room equipment have been tested or are under development. Especially the application of thermal-treatment, combined with wood compression or the use of renewable impregnation agents from regrowing plant materials (liquids with higher content of phenolic compounds from pyrolysisthermal treatment or hydro-thermal carbonisation processes) enhancec the possibility of eco-friendly methods of wood modification or wood impregnation. [ABSTRACT FROM AUTHOR]