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Thermo-hydro-mechanical (THM) processing can improve the intrinsic properties of wood, produce new materials, and give desired form and function to new applications. THM treatments change the mechanical properties of wood and may change its viscoelastic properties as well. Therefore, the objective of this study was to assess the viscoelastic properties of THM-treated wood at several humidity and load levels. To explore these changes, this study applied a THM treatment to beech (Fagus sylvatica L.) wood with steam (620 kPa) and heat (170 °C), followed by densification and increased temperature (200 °C) in a hot-press, which was then cooled while under pressure. Two initial specimen thicknesses before THM treatment were used to study the difference between density ratios. Specimens were tested in a humidity-controlled dynamic mechanical analyser (DMA) to apply creep stress with different loading levels (20% and 30% of expected modulus of rupture) and relative humidity levels (30%, 50%, and 65% RH). The creep compliance/recovery response was monitored, and dynamic moduli were measured before and after the application of creep stress. The loss modulus measured was highest for specimens tested at 65% RH and lowest in specimens tested at 30% RH, which is a direct result of the viscous response of the material. Increased damping of the specimens was also observed at higher RH, which is typical for wood products due to added moisture in the cell wall acting as a plasticizer to cell wall polymers. Like previous studies, THM treatment lowered the equilibrium moisture content (EMC) of densified wood specimens, which affected their mechanical performance. THM treatment yields higher strength and lower EMC, suggesting that this product could be suitable for structural applications where their service life is in an indoor environment. THM treatment also resulted in decreased creep compliance and recovery compliance as compared to control specimens. [ABSTRACT FROM AUTHOR]

Grape cane is a necessary annual by-product of a vineyard. It is available in large quantities, an estimated 9 million tons (oven-dry weight) annually, having approximately 18 million acres worldwide. There is currently no substantial commercial utilization of grape cane fiber, with the majority incinerated. The main objective of the current study is to characterize grape cane fibers extracted at different alkali treatment concentrations and to determine the optimum treatment concentrations that can produce better fiber properties. The fibers were treated at 1, 3, 5 and 7 wt% of sodium hydroxide (NaOH) at 100 °C for 2 h. The grape cane fibers can be categorized into two types, namely outer bark (OB) and inner bark (IB) fiber after the treatment process. Aspect ratio, chemical composition, crystallinity, changes in the functional groups using FTIR, and tensile properties of OB and IB fibers were investigated. The results show that these two fibers demonstrated dissimilar anatomical structures, cell types, cell dimensions, and tensile properties. Meanwhile, the chemical compositions and crystallinity are equivalent to each other. The overall properties of both fibers were found superior at the lower treatment concentrations. [ABSTRACT FROM AUTHOR]

The purpose of this paper was to analyze the effects of various OSB-strand modifications on physical and mechanical properties of strand board. Norway spruce (Picea abies L. Karst) strands were acetylated using acetic anhydride or thermally modified at 180 °C using atmospheric pressure and superheated steam environment. Strand boards made of acetylated strands (Acet), thermally modified strands (TM) and thermally modified strands used only at surface layers (TMSL) were produced. Furthermore, strand boards with 20% (Cork20%) and 40% (Cork40%) cork particles were manufactured. Wood-water relations, i.e., equilibrium moisture content (EMC), water absorption (WA), thickness swelling (TS), as well as mechanical properties, i.e., bending strength and internal bonding, were tested and compared to untreated reference strand board. The EMC for TMSL was no different than the reference boards, however, the other boards had a statistically significant decrease in EMC. Acetylated strand board and boards with cork particles had a significant increase in water resistance. The mechanical properties decreased for TM and Cork40%, but no difference was shown for Cork20%. Acetylation increased internal bond strength. The results provide a comparison between different modifications of strand boards and show a new possibility of reducing the water effects on OSB with cork particles. [ABSTRACT FROM AUTHOR]

Technical advancements in the field of capacitive sensing and the availability of multi-channel capacitance-to-digital converters have led the way for improved sensing capabilities in the field of wood moisture content. A four-channel, planar capacitance sensor was developed and calibrated on maple veneers. The calibration material was conditioned to equilibrium at three different relative humidity levels. Optimal penetration depths were determined statistically and analytically. A rule of mixture approach and a volumetric model were applied to derive the moisture content at distinct layers. Different levels of discrepancy of the fit were observed among and within the different electrodes and calibration datasets. The sensor was able to determine changes in moisture content and positive moisture content gradients, rather than averages, with the limitation of detecting negative moisture gradients. [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]

The bondability/glueability of aged and sanded thermo-hydro-mechanically (THM) densified beech wood ( Fagus sylvatica L.) was tested and compared with undensified sanded beech wood as a control. THM and control specimens were bonded with five different soy protein isolate (SPI) based adhesives. Commercial SPI powder was thermally modified in the vacuum chamber at 50 or 100 °C and pH adjusted (to pH 10.0) dispersions in water prepared at 24, 50 or 90 °C. Wettability was determined with measuring the sessile drop contact angles of water. Effective penetrations (EPs) and tensile shear strengths of THM and control specimens were determined. THM and control wood had similar wettability. Although THM wood had lower moisture content than control wood, it absorbed the water more slowly than control wood. THM specimens showed lower EPs than control specimens when comparing individual adhesives due to increased density of THM wood. Adhesives prepared with SPI thermally modified at 50 °C showed statistically significantly lower tensile shear strength of bonded THM specimens than that of bonded control specimens. THM densification had no significant effect on the bonding strengths of adhesives prepared with non-modified SPI and SPI thermally modified at 100 °C. [ABSTRACT FROM AUTHOR]

Spruce ( Picea abies L. Karst) wood lamellae, thermally treated at 170, 190, 210 and 230 °C were surface densified by compression at a temperature of 150 °C to three degrees of compression. Immediate springback, set recovery, mechanical properties in 3-point flexure, Brinell hardness and density profiles measurements were used to determine the effect of thermal treatment on the properties of surface densified wood. The highest immediate springback occurred in wood specimens thermally treated at the highest temperature (230 °C) and decreased with decreasing thermal treatment temperature. The untreated samples had the highest set recovery, which decreased with the temperature of thermal treatment. The surface densification increased hardness and bending strength. The highest increase was in the case of untreated wood and decreased with the temperature of thermal treatment. The modulus of elasticity (MOE) and modulus of rupture (MOR) of surface densified wood decreased with increasing thermal treatment temperature. The trend was similar for specimens which were thermally treated but not surface densified. Surface densification increased the density of the specimens in the first few millimetres below the surface. The highest density was achieved in untreated specimens and the lowest in specimens thermally treated at the highest temperature. [ABSTRACT FROM AUTHOR]

Microscale X-ray computed tomography (XCT) is discussed as a technique for identifying 3D adhesive distribution in wood-adhesive bondlines. Visualization and material segmentation of the adhesives from the surrounding cellular structures require sufficient gray-scale contrast in the reconstructed XCT data. Commercial wood-adhesive polymers have similar chemical characteristics and density to wood cell wall polymers and therefore do not provide good XCT attenuation contrast in their native form. Here, three different adhesive types, namely phenol formaldehyde, polymeric diphenylmethane diisocyanate, and a hybrid polyvinyl acetate, are tagged with iodine such that they yield sufficient X-ray attenuation contrast. However, phase-contrast effects at material edges complicate image quality and segmentation in XCT data reconstructed with conventional filtered backprojection absorption contrast algorithms. A quantitative phase retrieval algorithm, which isolates and removes the phase-contrast effect, was demonstrated. The article discusses and illustrates the balance between material X-ray attenuation and phase-contrast effects in all quantitative XCT analyses of wood-adhesive bondlines. [ABSTRACT FROM AUTHOR]

The importance of adhesion in production of wood-based composites is well-known. Adhesive penetration and interphase morphology play an important role in bond strength and product performance. Many studies offered different methods for interphase characterization and analysis. Both qualitative and quantitative methods have been used to analyze the bondline. Most of the quantitative methods were developed for bonded assemblies of veneer or wood blocks. Adhesive penetration measurement in particulate wood-based composites is the main scope of this study. For this purpose, uniform oriented strand board with veneer strands was produced by the use of phenol formaldehyde resin with 2, 6, and 10 % strand moisture content (MC). The strands were formed into well-organized mats to achieve a uniform structure for the composite. Cross-section specimens were prepared from each board and observed by epifluorescence microscopy. Six positions for growth-ring angle in adhesive joints were denoted to evaluate penetration in different directions of the wood. Four parameters were also determined to quantify resin penetration patterns by counting the quantity of the main anatomical elements of wood, which were filled with resin. Finally, it was determined that this method could recognize the differences between adhesive penetration in boards produced with different level of strand MC. Resin penetration in strands with 6 and 10 % MC was the greatest. Growth-ring angle of the strands influenced penetration as it was increased when both strands meet each other in an oblique position, although this effect was significant only in maximum penetration depth in fibers. [ABSTRACT FROM AUTHOR]

In this study, birch ( Betula pendula L.) veneers were simultaneously densified and dried using a contact drying method at pressures of 1.5 and 3 MPa at 130 °C and compared with veneer dried in a laboratory-scale convective type dryer. Compression rate, thickness swelling, and the density profiles of the veneers were investigated. Furthermore, the microstructure of densified veneers was studied by scanning electron microscopy (SEM). A maximum veneer compression rate of 9 % was achieved at a pressure of 3 MPa. Under these conditions, the veneers were, on average, densified from 504 to 574 kg m (approximately 14 %). After water soaking, full set-recovery-recovery to the initial thickness-occurred. However, the swelling rate was lower for the densified veneer. Density profiles measurements showed that densification occurs throughout the veneers. The SEM images showed that the surface of the densified veneers were smoother, whilst no cracks were detected due to densification. Densification seemed to occur in vessels. Typically, rays were bent when there was a vessel nearby. [ABSTRACT FROM AUTHOR]

Viscoelastic thermal compression (VTC) is a type of thermal-hydro-mechanical (THM) processing that requires only a short processing time. THM processing causes some chemical transformations, the nature and extent of hydro-thermolysis depends on the special treatment conditions and the chemical nature of wood species. In the present study, the chemical transformations of the cell wall components and wood extractives during VTC treatment were investigated, and correlation between chemical characterizations and observed property changes was analyzed. For this purpose, the content of extractives and pH values were determined, and FTIR analysis was performed on extractable substances, extract-free wood, holocellulose, α-cellulose and lignin. Two temperatures and two steam exposure times were adopted to determine the influence of processing conditions on chemical characterization of Tsuga heterophylla. The results revealed that THM treatment caused a series of chemical reactions in extractives. Treatment temperature and conditioning time have significant influence on chemical changes of extractives. For all of the VTC treatments used in this study, no significant changes occurred in the lignin and α-cellulose components. The only significant chemical changes occurred in the hemicelluloses, which were primarily reduction of carbonyl and acetyl functional groups. This study also confirmed that the chemical transformation of wood correlates with property changes of VTC wood. [ABSTRACT FROM AUTHOR]

A phenol formaldehyde (PF) adhesive was uniformly tagged with iodine such that it yielded sufficient X-ray computed tomography (XCT) gray-scale contrast for material segmentation in reconstructed wood-composite bondlines. Typically, untagged adhesives are organic and have a similar solid-state density as wood cell-walls, and therefore cannot be segmented quantitatively in XCT data. The iodinated PF development involved analysis and comparison of three trial adhesives containing rubidium, bromine, or iodine. Adhesive tag efficacy was measured in terms of X-ray absorption contrast enhancement and tag uniformity along the adhesive polymers. Cured adhesive density, tag element, and concentration were each found to significantly impact XCT contrast results, which in turn agreed with theoretical X-ray attenuation predictions for each resin. Ion chromatography confirmed the absence of free iodide in the liquid PF prior to bonding, and fluorescence microscopy and energy-dispersive spectroscopy (EDS) showed that iodine tags remained associated with the cured adhesive polymers. XCT and EDS results also demonstrated that when contrast agents are simply mixed into resins, rather than attached to the polymer chains, they are free to migrate independent of the penetrating adhesives during bonding. This then can cause complications with quantitative segmentation and analyses. The iodinated PF yielded consistent and uniform XCT gray-scale contrast; its formulation could be adjusted for other viscosity or molecular weight distribution, which would affect its penetration behavior. [ABSTRACT FROM AUTHOR]

Hybrid poplar ( Populus deltoides × Populus trichocarpa) and Douglas-fir ( Pseudotsuga menziesii) wood specimens were densified with three variations of thermo-hydro-mechanical (THM) treatment. The THM treatments differed in the steam environment, including transient steam (TS), saturated steam (SS), and saturated steam with 1-min post-heat treatment at 200 °C (SS+PHT). The bending properties, FTIR spectra, and colour of the THM wood specimens were studied before and after exposure to two different wood decay fungi, brown rot Gloeophyllum trabeum, and white rot Trametes versicolor. The results showed that the performance of densified hybrid poplar wood was considerably poorer than the performance of Douglas-fir heartwood. The FTIR spectra measurements did not show changes in the densified hybrid poplar wood, while some changes were evident in densified Douglas-fir specimens. After fungal degradation, the most prominent changes were observed on the SS+PHT specimens. Colour is one of the most important parameter predominantly influenced by the wood species and the intensity of the densification process for both wood species, while after fungal exposure, the colour of all densified Douglas-fir specimens obtained more or less the same appearance, and densified hybrid poplar specimens resulted in lighter colour tones, indicating that the pattern of degradation of the densified and non-densified specimens are similar. The 3-point bending test results determined that the THM treatment significantly increased the modulus of rupture (MOR) and modulus of elasticity (MOE) of the densified wood specimens, while fungal exposure decreased the MOE and MOR in hybrid poplar and Douglas-fir specimens. [ABSTRACT FROM AUTHOR]

Copyright of European Journal of Wood & Wood Products / Holz als Roh- und Werkstoff is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of European Journal of Wood & Wood Products / Holz als Roh- und Werkstoff is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of European Journal of Wood & Wood Products / Holz als Roh- und Werkstoff is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of European Journal of Wood & Wood Products / Holz als Roh- und Werkstoff is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The paper describes for the first time the analysis of the structure of compressed wood using computed tomography. The anatomical structures of Douglas-fir and hybrid poplar before and after densification with the viscoelastic thermal compression (VTC) process were described by pore size distributions and mean pore sizes and compared. The compression of Douglas-fir mainly affected earlywood, while the compression of hybrid poplar mainly occurred in the vessels. In both wood species, the densification resulted in a significant decrease in the pore volumes. The porosity decreased to less than half of the original value for Douglas-fir earlywood and to approximately one-quarter for the vessels in hybrid poplar. The relevant mean pore sizes also decreased dramatically to about one-quarter compared to the original values. In contrast, latewood in Douglas-fir and libriform fibers in hybrid poplar are quite stable under compression. Douglas-fir latewood retained its original structure after compression and did not show any reduction in pore size. The results confirmed that the anatomical structure of VTC densified wood can be described by pore size distributions and mean pore sizes. However, in the case of broad or bimodal distributions, the mean pore sizes are of less significance. [ABSTRACT FROM AUTHOR]

Low-density hybrid poplar wood ( Populus deltoides × Populus trichocarpa) was densified by mechanical compression under saturated steam, superheated steam, and transient conditions at temperature levels of 150, 160, and 170°C. Furthermore, compression of wood under saturated steam conditions at 170°C, followed by post-heat-treatment at 200°C for 1, 2, and 3 min, was performed. To determine the influence of compression treatment on the set recovery, specimens were subjected to five cycles of water soaking and drying. Modulus of rupture (MOR) and modulus of elasticity (MOE) of specimens compressed under saturated steam conditions at 170°C and post-heat-treated at 200°C were determined in the dry condition and after five soak/dry cycles. Higher temperature of the compression treatment resulted in lower equilibrium moisture content, while the steam conditions during the treatment and the post-heat-treatment did not have significant effect. Furthermore, the highest degree of densification was obtained in specimens compressed under saturated steam conditions at 170°C and post-heat-treated at 200°C. The steam condition and temperature influenced the set recovery of compressive deformation. Reduced hygroscopicity does not necessarily imply reduced set recovery. The results established that considerable fixation of compressive deformation can be obtained by compressing the wood in a saturated steam environment and by post-heat-treatment at 200°C. The short heat-treatment had no influence on MOR or MOE, but soaking/drying treatments caused a decrease in the MOR and MOE. [ABSTRACT FROM AUTHOR]

In this paper, the compressive deformation of hybrid poplar wood ( Populus deltoides × Populus trichocarpa) at high temperature (150, 160, and 170°C) and under various conditions of steam pressure was studied. Temperature and conditions of steam environment affected the relative density change and creep deformation during compression, as well as properties of the resulting densified material. While the temperature significantly affected the compression deformation of specimens compressed under transient and superheated steam conditions, temperature within the range studied had little effect on the compressive deformation in saturated steam. In all tested conditions, compression deformation was achieved without cell wall fractures. Higher temperature of compression, regardless of steam condition, resulted in lower equilibrium moisture content. In specimens compressed under saturated steam, the modulus of rupture (MOR) and modulus of elasticity (MOE) were increased proportionally to the increase in density, while the compression under superheated steam produced lower increase in the MOE and MOR than expected based on the increase in density. Compression in transient steam conditions at 170°C produced densified wood with higher MOE and MOR than expected based on the increase in density. [ABSTRACT FROM AUTHOR]

Density profile relation to hardness of VTC wood composites was evaluated using X-ray densitometry and modified Brinell hardness method using different applied forces. Moreover, surface elasticity was evaluated. Prior to lamination, the low-density hybrid poplar ( Populus deltoides × Populus trichocarpa L.) and Douglas-fir ( Pseudotsuga menziesii L.) thin boards were compressed to 1.22 or 1.14 g/cm, respectively. Two different kinds of laminations were made, either single layer of 1.5 mm thickness or two 1.5-mm layers bonded to unmodified wood. The results show that thicker laminate has a great positive influence on Brinell hardness. This study suggests that results from the existing method for Brinell hardness are not comparable, and if applied force is chosen without restraint, the effect on the hardness value is significant for inhomogeneous wood composites. [ABSTRACT FROM AUTHOR]

Copyright of European Journal of Wood & Wood Products / Holz als Roh- und Werkstoff is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Low-density hybrid poplar ( Populus deltoides × Populus trichocarpa) was densified with the viscoelastic thermal compression (VTC) process to three different degrees of densification (63%, 98%, and 132%). Durability of the VTC treated specimens was assessed by exposure to two white rot fungi ( Pleurotus ostreatus and Trametes versicolor) for four or eight weeks. After incubation, mass loss in grams and percentage mass loss were determined. The results showed that VTC densification did not change decay resistance to Pleurotus ostreatus and Trametes versicolor. The mass losses caused by Trametes versicolor were more extensive than those by Pleurotus ostreatus. As expected, longer exposure time resulted in higher mass loss. Furthermore, the degree of densification did not influence susceptibility to fungal degradation. [ABSTRACT FROM AUTHOR]

The vertical density profile of wood-based composites is often measured using X-ray densitometry. During preliminary studies, in which the density profiles of wood composites with discrete layers of varying density were measured, it was observed that the absolute density values of the layers were incorrect when compared to gravimetric measurements of the individual layers. This is due the recommended calibration process of the X-ray densitometer, which uses the overall density of the composite to determine the X-ray attenuation factor. The severity of the error increases with the difference between minimum and maximum density in the profile. [ABSTRACT FROM AUTHOR]

A correction to the article "The Wettability and Bonding Performance of Densified VTC Beech (Fagus sylvatica L.) and Norway Spruce ( Picea abies (L.) Karst.) Bonded With Phenol-Formaldehyde Adhesive and Liquefied Wood" that was published online on February 21, 2013 is presented.