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This paper presents numerical modelling of the ballistic impact response of hybrid laminated structures, which are developed through combinations of ceramics, Ultra-High-Molecular-Weight Polyethylene (UHMWPE), Kevlar and compressed wood. It is, for the first time, to embed the compressed wood in the ballistic panel and numerically investigate the impact response of the hybrid structures made of the multiple constituent materials. Different constitutive models and the related failure criteria were employed in the modelling to capture the ballistic responses of the constituent materials and hybrid structures. The numerical simulations were compared with the corresponding experimental results with acceptable correlation. The essential features of the hybrid composite structures subjected to high velocity impact were simulated by the finite element (FE) models, such as deformation and failure modes, back-face signature and the residual velocities. The FE models developed are ready to be used to assist design lightweight composite armour with optimized ballistic resistance and self-weight.

Copyright of China Forest Products Industry is the property of China Forest Products Industry Editorial Office 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.)

Building with cross laminated timber (CLT) has gain increased interest over the last years, but in common to other wood-based building systems, inadequate low-frequency sound insulation is seen as a problem. This paper deals with two methods to improve the sound insulation of CLT panels, normally made from spruce: 1) heavy CLT, introducing compressed, i.e. densified, spruce as well as alternative wood species, and 2) elastic layer based upon shear motion. In addition to a series of laboratory measurements, a full-scale CLT floor made of two 60 mm birch panels with a 12 mm elastic layer in between was tested in a two-room test mock-up. The results from the acoustical measurements showed that the floor has about 7 dB greater airborne and impact sound insulation for one-third octave bands, 50–3150 Hz, compared to a standard CLT floor of the same total height.

This paper reports on multiple stage bleaching and its effect on the mechanical and swelling properties of compressed wood (CW). The natural wood specimen was bleached with NaClO2 in five steps and three hot-pressing conditions. Their effects were investigated in morphologies: lignin content, alpha-cellulose content, compression ratio, mechanical properties, swelling and, water contact angle. After compression, the wood specimens became dense and the most porous structures collapsed. The lignin content decreased as the bleaching steps progressed, and the highest alpha-cellulose content was observed at the third bleaching step. This CW showed the best mechanical properties: bending strength was 240.1 ± 35.7 MPa, and Young's modulus was 23.08 ± 0.89 Gpa. The CW swelling decreased as the bleaching step progressed, and was associated with the density decrease and the compression ratio increase with the bleaching step. The B3 is an optimum bleaching step that accounts for the best mechanical properties, which might be associated with the highest alpha-cellulose content. [ABSTRACT FROM AUTHOR]

To reveal the existence of p -hydroxyphenyl (H) units in compressed wood lignin, four different milled wood lignins were extracted using Pinus massoniana Lamb compressed wood, Pinus massoniana Lamb normal wood, and sugarcane bagasse as raw materials. Then, three dehydrogenation polymers (DHPs) were synthesized using coniferyl/ p -coumaryl alcohol as raw materials to reveal the interunit linkages of H units. The lignin and DHP samples were systematically characterized by 1H, 13C, 2D HSQC, and 31P NMR techniques. Compared with the opposite wood milled wood lignin (OW-MWL) and the normal wood milled wood lignin (NW-MWL), the compressed wood milled wood lignin (CW-MWL) contained a large amount of H units, and the H/G ratio and the p -hydroxyphenyl OH group contents were 0.15 and 1.09 mmol/g, respectively. Through the characterization of CW-MWL and DHPs, it was revealed that p -hydroxyphenyl units mainly coupled with other units by β-O-4, β-β, and β-5 linkages. Compared to the sugarcane bagasse milled wood lignin, it was clearly demonstrated that the H unit rather than p -coumarate ester occurred in CW-MWL. This study comprehensively explored the structural characteristics and linkages of H units in compress wood lignin, and provided useful information for revealing the participation of H units in the construction of lignin macromolecules. • More p -hydroxyphenyl unit was quantified in the compressed wood lignin. • More p -hydroxyphenyl units lead to a decrease of β-O-4 and β-5 linkages. • The main interunit linkage of G-DHP, H-DHP, and GH-DHP were β-O-4, β-β, β-5. • The p -hydroxyphenyl unit was presented as β-O-4, β-β, β-5 in the compressed lignin. [ABSTRACT FROM AUTHOR]

The widespread use of adhesives in timber construction has negative implications for the end-of-life disposal or re-use of the structural timber components. To promote the circular bioeconomy, it is preferable to substitute adhesives with more sustainable alternatives such as wood-based connectors. Today, robotic fabrication technologies facilitate the development of dowel-laminated timber (DLT) products whereby hardwood dowels are used to connect timber laminates as a substitute to adhesives. In recent years, thermo-mechanical densification of wood has resulted in significant improvements in the mechanical performance of the wood. This modified product often termed compressed wood (CW) has a shape-recovery effect which may be beneficial for the development of DLT products and timber-timber connections with improved friction fit with time. To test the hypothesis, accelerated ageing tests were carried out on CW-timber and hardwood-timber dowel type connections subjected to variable climate conditions. Finally, the capacity of the connections or friction fit was assessed using pull-out tests. Results show that the shape-recovery effect leads to the continuous expansion of the CW dowels and facilitates a friction fit with the timber substrate yielding higher pull-out loads when compared to hardwood dowels. [ABSTRACT FROM AUTHOR]

Cross-laminated timber (CLT) is an innovative wood product that can be used to build midrise and tall wood construction as an alternative to concrete, masonry, and steel. As floor, roof, and wall made of CLT is subjected to out-of-plane bending, rolling shear (RS) failure of cross-layers can arise prior to bending failure of the outermost layers, which governs the load-carrying capacity of CLT. In fact, the global deflections of CLT depend on the rolling shear modulus of cross-layers, which is much lower than shear modulus parallel to grain. Therefore, it is necessary to determine and improve the rolling shear strength and modulus of cross-layers. In this paper, several test methods were firstly summarized, after which the main influence factors on rolling shear properties were reviewed. Finally, seven configurations of hybrid CLT with three layers were tested to assess the rolling shear properties of hybrid CLT, in which the outer layers are made of Spruce-Pine-Fir (SPF) and the cross-layer is made of different materials such as birch, compressed wood (CW), laminated veneer lumber (LVL), Parallel strand lumber (PSL), plywood, oriented strand board (OSB), and glued laminated bamboo (GLB). The CLT made of SPF was also tested, whose rolling shear properties were regarded as reference. The rolling shear properties of GLB are about twice as high as those of SPF. Other materials do not exhibit superior rolling shear properties to SPF. The compressed wood shows a significant ductility in rolling shear failure. [ABSTRACT FROM AUTHOR]

The moisture-induced recovery of compressed wood is one of the major problems of wood densification technology. Achieving a cost-efficient surface densification process without the need for additional resins to eliminate the set-recovery may lead to an increase in value of low-density wood species. A previous study has shown that a pre-treatment with ionic liquids (ILs) can nearly eliminate the set-recovery. It was however observed that during the pre-treatment process the IL did not penetrate sufficiently deep into the wood to explain the achieved reduction in set-recovery. Based on these findings, the hypothesis was posed that further penetration of the IL into the wood occurs during the densification stage as a consequence of the applied heat and pressure. Thermo-gravimetric analysis (TGA) and gas-chromatography mass-selective-detection (GC-MSD) showed that the depth of penetration of the IL was greater after the densification process than before. Digital image correlation (DIC) showed that in regions with a high IL concentration, there was almost no set-recovery, and it gradually increased with a decrease in the IL concentration, as observed with TGA and GC-MSD analysis. [ABSTRACT FROM AUTHOR]

The objective of the research was to densify wood of Cupressus lindleyi, Cedrela odorata, Swietenia macrophylla, Tabebuia donnellsmithii, Fraxinus uhdei, Fagus mexicana, Dalbergia paloescrito and Guazuma ulmifolia. The densification of the wood increases its apparent density, its wave speed and its dynamic modulus; to verify this, before and after the procedure, measurements of these values were taken. This artificial increase in the apparent density of the wood and the consequent increase in its dynamic modulus can mean a technological gain in the transformation and modification of the intrinsic properties of this material. The eight woods investigated are potentially candidates for densified treatment. [ABSTRACT FROM AUTHOR]

Mechanical densification treatments make it possible to increase the density of low- or moderate-density woods, and thus a high mechanical strength of densified wood and high-value products can be obtained. The authors' previous treatments showed that the diffusion and distribution of steam and the release of vapor inside densified wood were prevented to some extent during thermo-hydro-mechanical (THM) densification, causing the occurrence of protrusions, carbonization, blisters, and blows. This study aimed to overcome these problems. Based on the authors' previous THM densification, different materials, such as fabric, metal mesh, metal foam, and sintered metal mesh laminate (SMML), were used to improve the process. Densification was tested on different wood species. The results showed that SMML was the preferable material for THM densification through enhancing diffusion and distribution of steam, and evaporation of moisture inside wood. No protrusion, carbonization, blisters, or blows were found after densification with SMMLs. The densified wood specimens showed uniform color and a neat surface. [ABSTRACT FROM AUTHOR]

Oil palm wood (OPW) extracted from the oil palm trunks and subjected to a four-step compreg method consisted of drying, impregnation, re-drying and hot-pressing densification process. For the densification process, four different pressing cycles (involving 1-3 cycles) were proposed and conducted with three pressing durations (30, 35 and 40 min). Properties of the compreg OPW were evaluated. The results revealed that the samples compressed using the pressing process with more than 1 cycle displayed significantly better water absorption and thickness swelling. OPW samples that compressed with longer pressing durations also reported better performance and the formaldehyde emission decreased along with extending pressing durations. However, the improvement was not statistically significant, therefore, 30 min pressing duration is sufficient to achieve satisfied properties. [ABSTRACT FROM AUTHOR]

The recovery behavior and selected mechanical properties were studied for Populus tomentosa wood subjected to surface compression followed by heat treatment. The surface compression of wood was carried out in an open hot-pressing system at 180 °C with compressed thickness of 2 to 18 mm. The surface-compressed wood was treated by atmospheric heat treatment or 0.30 MPa pressurized superheated-steam heat treatment at 180 °C for 2 h. The results showed that the set recovery of compressed wood decreased with increasing compressed thickness before posttreatment. Atmospheric and pressurized heat treatment reduced the average set recovery of compressed wood significantly from 12.9% to 4.1% and 1.5% respectively, after conditioning at 40 °C and 90% relative humidity. Moreover, mechanical properties including the modulus of elasticity (MOE), modulus of rupture (MOR), hardness, and surface hardness increased with elevating compressed thickness. Both atmospheric and pressurized heat treatment reduced the MOR, hardness, and surface hardness of compressed wood. Analysis of variance showed that the effects of heat treatment on mechanical properties was not significant, except pressurized heat treatment decreased hardness significantly. With a compressed thickness of 10 mm, MOE, MOR, hardness and surface hardness were increased by 52.6%, 36.4%, 122.0% and 129.6%, respectively, compared with untreated wood. [ABSTRACT FROM AUTHOR]

To expand the applications of low-density wood, solid white poplar (Populus tomentosa) wood with a moisture content of 10.6% was compressed 5 mm radially at 90 °C, 120 °C, 150 °C, 180 °C, and 210 °C, and the density profile characteristics were analyzed. It was found that compressed wood with a non-uniform density profile contributed to the peak density and average density of the compressed layer, where the highest values were 0.87 g/cm3 and 0.72 g/cm3, respectively. The density peak and compressed layer were formed at various distances from the wood surface according to the pressing temperatures tested. It was concluded that the pressing temperature had a great effect on the density profile of the compressed wood and the pressing temperature effectively controlled the shape of the density profile. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the performance of diverse wood coating systems on THM-densified spruce wood. For this purpose, Norway spruce [Picea abies K.] was thermo-hydromechanically densified in a closed system, under pressure and steam. Five different types of solventand water-based coating systems were applied. To assess the interaction of the coatings and the densified wood, following tests were carried out: exposure to UV light, water permeability and climatic variation. The color of densified wood is more stable to UV light than non-treated wood and the coating system has insignificant influence on color change. When specimens are exposed to a short-term change of climatic variation, the total volume change is less than 5% on uncoated densified wood, neglectable if coated. In case of long-term variation, (specimens exposed until constant weight), the protection effect of the coatings is less significant. The total volume change is appr. 8%. Therefore, if coatings are partially preventing moisture and water uptake of densified wood at short term exposure, they confer limited protection at long term exposure. Moreover, there is not significant performance difference within the different kinds of coating systems. [ABSTRACT FROM AUTHOR]

Bamboo has attracted increasing interest for its promising application and usage in sustainable structural purposes. Bamboo node is crucial in improving stiffness and stability of bamboo under wind load. However, the structural role of node distribution in bending deformation has not yet been fully understood. This paper studied the effects of node distribution on bamboo outer diameter compression both theoretically and experimentally. A loaded bamboo model was set up to deduce the formula for its calculated compression. One loaded bamboo (Phyllostachys pubescens) with 42, 11 or 0 node was measured to obtain the measured compression values. The calculated and the measured compressions showed that the outer diameter compression of the bamboo with 42 nodes was lower than the bamboo with 11 nodes, and much lower than that without node. Bamboo nodes effectively reduced the outer diameter compression, and the more nodes, the smaller the compression value. Nodes also kept compression from 0.16 to 2.04 mm. Bamboo nodes played a vital role in avoiding strong bending deformation under wind load. This work could provide insights to help the bio-inspired design of advanced structures with desired bending deformation. [ABSTRACT FROM AUTHOR]

Inspired by stiffness difference in the “sandwich structure” of earlywood and latewood, surface-densified (SD) plywood was manufactured based on a hydro-thermal approach. A series of veneer moisture contents (MCs) and hot-pressing temperatures were selected to prepare the SD plywood. Great surface densification was observed according to density distribution through plywood thickness. The densification was attributed to the thermal softening and mechano-sorptive behavior of constituents in the wood cell wall. A greater degree of surface densification could be achieved at higher hot-pressing temperatures or higher surface veneer MCs. Final MCs of the SD plywood met the requirement of the Chinese national standard. No significant variation was observed for the bonding strength among SD and control (CK) plywood. Mechanical properties – including modulus of rupture (MOR), modulus of elasticity (MOE) and hardness – of the SD plywood were significantly higher than the CK plywood. The enhancements of MOR, MOE and hardness could be attributed to its high-density surfaces. The greatest increment of MOR, MOE and hardness was 54, 104 and 144%, respectively. Comparing to some domestic Chinese hardwood species, SD plywood possessed greater surface hardness with less average density. The results indicated that, inspired by the stiffness difference in the “sandwich structure” of wood, preparation of the SD plywood based upon hydro-thermal treatment is feasible. [ABSTRACT FROM AUTHOR]

To investigate the mechanism of shape fixation of steam-compressed wood, Japanese cedar wood specimens were compressed radially by 50% using saturated water vapor at 160 °C and observed during shape recovery in different liquids, including water and dimethyl sulfoxide (DMSO). Shape recovery was evaluated based on the dimensional changes in wet conditions (SRw) and those in dry conditions (SRd). SRw in DMSO was significantly greater than that in water, but this recovery observed in DMSO was not recognized in SRd. The contradiction arose from significant reversible cellular deformation: the compressed cells were reversibly expanded with the swelling of the cell wall, and this swimming ring-like cellular deformation increased SRw in DMSO. At room temperature, the SRd values in various liquids were closely connected to the swelling of the wood cell walls, rather than to the degree of softening. This suggested that the plastic expansion of cells, as well as the softening of the wood cell walls, caused the shape recovery of compressed wood. This mechanism was qualitatively expressed by an elasto-plastic model equipped with an inflator representing the swimming ring-like expansion of the cell lumina. [ABSTRACT FROM AUTHOR]

Results of a numerical analysis of the stress-strain state of wood during its pressing in different symmetry directions of the anisotropic material are presented. It is shown that the anisotropy of mechanical properties of wood is an important factor determining both the structural characteristics of the porous system and its strength. A mathematical modeling of the process of pressing wood as a three-phase anisotropic rheologically complex capillary-porous system allows one to predict parameters of the resulting wood composite. The compressed wood obtained by the production modes developed has a tensile strength eight times greater than that of the natural one, which is comparable to the strength of the St3 steel, but its specific strength is higher than that of the St45 steel. Compression and impregnation of softwood species with an aqueous solution of carbamide allows one to harden them. This kind of treatment endows the wood with enhanced strength characteristics comparable to the characteristics of the St3 steel. The special features of tensile tests used to estimate the elastic modulus and strength characteristics of such materials are considered. Data obtained by different testing methods are correlated, and characteristics of the strengthened wood and some brends of steel are compared. [ABSTRACT FROM AUTHOR]

Since human creation up to now, wood has been discussed as an important organic material, therefore its maintain and optimum usage is a considerable problem. From one hand, with due attention to condition of forest in Iran, using fast growing specie Paulownia provides new way in wood industries. But from other hand, this specie with low density has low strength. One of the suggested ways to increase density of this wood is its impregnation by resin and to compress it. In this research it is tried to increase the penetrability and impregnation of Paulownia by using urea formaldehyde resin at first pretreatment and then compression should be done. In order to perform this process, two variables pretreatment and compression percent were defined that each of them had two levels. The pretreatment was performed by NaCl and NaOH and 40, 50% compression. Totally, 72 samples were prepared and after producing the compressed wood, the absorption percent and mechanical properties were evaluated which included compression parallel to grain, modulus of rupture, modulus of elasticity in bending and impact strength. The results showed that the provided mechanical properties and pretreatments samples with NaCl had most values of these properties in 40 and 50% compression levels.

Copyright of Misr Journal of Agricultural Engineering is the property of Egyptian National Agricultural Library (ENAL) 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 Acta Silvatica et Lignaria Hungarica is the property of Sciendo 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.)

Bamboo as an eco-friendly material has potential as construction material and proves his suitability in use as an alternative for more traditional materials such as steel, aluminium and composite. This work presents the influence of humidity on mechanical properties of two different bamboos, Pseudosasa amabilis (or Tonkin Cane) and Pleioblastus amarus (or Ku Zhu) which are used for bicycle frames. A large number of tensile, compression and bending tests were carried out in two conditions, dry (in terms of the environment) and wet (after 3 weeks in wet chamber). It is shown that both, Tonkin Cane and Ku Zhu, in spite of low change in weight after 3 weeks in wet chamber have lower values of mechanical properties. The results show that the tensile, compressive and bending strength of bamboo significantly decreased after bamboo samples were kept in an environment with humidity level of 60%. The reduction of strength in the wet state for both types of bamboo is statistically proven by two sample comparisons of their arithmetic means at significance level α = 0.05. The results of this study indicate that the minimum change of moisture in samples decreases bending, tensile and compression strength of bamboo. Potential application of the results of this research is in the design and production of bicycle frameworks. [ABSTRACT FROM AUTHOR]

The present research was carried out to study the suitability of using agricultural residues as a raw material for producing pressed wood. Two types of agricultural residues (Rice straw and wood sawdust) were used. Experiments were conducted to study some different operating parameters (pressing temperature, sample thickness and resin ratio) affecting the pressing process. The produced particleboards were evaluated in terms of static bending strength (modulus of rupture and modulus of elasticity) and thickness swelling. Final quality of the produced particleboards was compared with the particleboard standard quality guidelines. The experimental results reveal that modulus of rupture (28.1, 39.8 MPa), modulus of elasticity (4530, 5030.2 MPa) and thickness swelling (6.3 and 3.9%) of the produced pressed wood from rice straw and wood sawdust, respectively were in the suitable region under conditions of 180°C pressing temperature and 8% resin ratio with acceptable sample thickness of 12 mm. Under these conditions, final quality of the produced particleboards was found to be very close with the particleboard standard quality guidelines. [ABSTRACT FROM AUTHOR]

Finite element models were, in the first time, developed to simulate the pre-stressing behaviour of Glulam beams with insertion of compressed wood blocks, which were further used to simulate the structural behaviour of the pre-stressed beams subjected to subsequent destructive bending. Here, both the Glulam and compressed wood were modelled as orthotropic elasto-viscoplastic materials. The moisture-dependent, including spring back, swelling of the compressed wood block and the creep of the Glulam were considered in the modelling. The models developed were validated against the corresponding experimental results, with reasonably good correlation in terms of the free swelling, the precamber, initial stress state of the Glulam beams reinforced and load-deflection relationships. With validated models, further studies were then undertaken to investigate effects of the thickness, depth and spacing of compressed wood blocks on the precamber, initial bending stiffness and ultimate load carrying capacity of the beams pre-stressed. The results indicate that there are significant enhancements on the precamber (up to 1/288 of the deflection/span ratio), the initial bending stiffness (up to 23.8%) and the ultimate load carrying capacity (up to 10.4%). [ABSTRACT FROM AUTHOR]

Oil palm trunks are a by-product of oil palm plantations and provide raw material to the woodworking industries. However, their resistance against degradation by termites needs to be improved; this study investigated hot pressing as a chemical-free method to improve resistance. The main objective was to assess resistance to termites conferred to oil palm wood by hot pressing at various temperatures (140, 180, and 220 °C) for a fixed duration of 8 min and maximum pressure of 2 MPa. The samples were the only available nutrition to subterranean termites (Coptotermes gestroi Wasmann) in a 4-week no-choice test. The thermally compressed oil palm wood did not show any significant effect of the pressing temperature on mass loss, but the surface damage to the samples with treatment at 220 °C indicated improved resistance to subterranean termites based on visual observation.

Compressed wood, which is formed by a process that increases the wood’s density, aims to improve its strength and dimensional stability. Compressed wood can be used in building and construction, especially for construction of walls and flooring. Currently, supplies of wood are becoming limited, and the oil palm tree has become one of the largest plantation species in Malaysia. Oil palm trunk could be an appropriate choice for an alternative source for compressed wood. This paper aims to review the current status of oil palm biomass, including the availability of this tree, in order to illustrate the potential of oil palm biomass as an alternative source for compressed wood. Up to the present there has been insufficient information regarding the manufacturing conditions and properties of compressed wood from oil palm trunk. This paper will cover the background of compressed wood and the possibilities of producing compressed wood using oil palm trunk as a raw material.

A new approach to strengthen glulam beams by using compressed wood was introduced by author. Compressed wood (CW) is made of a lower grade wood, which is densified in the radial direction under specific pressure and temperature conditions. In order to optimize the structural performance of glulam beams reinforced by compressed wood, in terms of load carrying capacity, strength and stiffness, parametric studies were carried out on thickness, depth and space of CW blocks. In this study, the dimensions of the beam models were 3800 mm in length, 120 mm in width and 200 mm in depth which comply with the requirements from Eurocode 5, and BS EN 408:2003, where the ratio between the span and the depth equals to 18. There are nineteen beams simulated in the parametric studies using validated FE models. The parameters covered in the simulations include the thickness, depth and spacing of CW blocks, however the CW block width and beam dimensions were remained unchanged. The results indicate that there are significant enhancements on the pre-camber (up to 1/288-deflection/span ratio), initial bending stiffness (up to 23.84%) for a beam reinforced by seven CW blocks with a thickness and depth of 50 mm and 95 mm respectively and ultimate load (increased to 10.4%) of glulam beams reinforced by seven CW blocks with thickness of 40 mm. [ABSTRACT FROM AUTHOR]

This paper explores changes in the quality of the surface of aspen wood after pressing. Pressing, a type of processing, facilitates changes in surface quality and smoothness, thereby producing wood suitable for the furniture industry. The results obtained for the pressed wood surface were compared with those obtained for wood surfaces that were not subjected to pressing. Attention was paid to the impact of moisture, the degree of compression, and plasticizing by steam. The change in smoothness/roughness was monitored in both the longitudinal and transverse directions (relative to the grain). The contact method was used to measure the roughness both before and after pressing. The independent variables of moisture content and degree of compression had the greatest impact on the smoothness/roughness. Plasticizing by steam had no greater impact. Therefore, the non-plasticized aspen wood was determined to be more suitable for the given purpose. [ABSTRACT FROM AUTHOR]

The objective of this research was to determine the influence of wood species (Fagus sylvatica L. and Populus tremula L.), thickness (4, 6, 10, 18 mm), and degree of densification (0%, 10%, and 20%) on the impact bending strength (IBS) and Brinell hardness (BH) in the radial direction. Three-factor analysis of variance confirmed that the difference in IBS was significantly related to the wood species and wood thickness. Wood densification did not have a significant effect on IBS. In addition, beech wood exhibited higher IBS values than aspen wood. The IBS values increased proportionally with increasing thickness. All factors affecting Brinell hardness were statistically significant, although thickness had the smallest influence overall. The Brinell hardness values were substantially higher in beech wood than aspen wood, and in some cases were more than three times greater. On the other hand, densification exhibited a more positive effect on increasing Brinell hardness for aspen wood than beech wood. [ABSTRACT FROM AUTHOR]

Hygrothermal recovery (HTR), the dimensional changes in wood induced by hygrothermal treatment, was investigated using both compression and normal wood of sugi ( Cryptomeria japonica). The elastic released strain of growth stress was measured on living tree surfaces; subsequently, the specimens were taken from the same position to measure HTR. HTR was measured as dimensional changes due to treatment at 20, 40, 60, 80, and 100 °C in hot water ranging from 200 min to 177 days. The intensity of HTR had a positive relationship with elastic released strain of growth stress. This result suggests that HTR is the relaxation of the viscoelastic component of growth stress accumulated during the maturation process of trees. The rate of HTR clearly showed a time-temperature dependency: higher at higher treatment temperatures and lower at lower treatment temperatures. Based on kinetic analysis, the apparent activation energy ( E) was calculated as 407 kJ/mol, which is similar to the published E of lignin softening implying that the HTR is a lignin-related phenomenon. [ABSTRACT FROM AUTHOR]

The density of wood can be increased by compressing the porous structure under suitable moisture and temperature conditions. One aim of such densification is to improve surface hardness, and therefore, densified wood might be particularly suitable for flooring products. After compression, however, the deformed wood material is sensitive to moisture, and in this case, recovered up to 60 % of the deformation in water-soaking. This phenomenon, termed set-recovery, was reduced by thermally modifying the wood after densification. This study presents the influence of compression ratio (CR = 40, 50, 60 %) and thermal modification time (TM = 2, 4, 6 h) on the hardness and set-recovery of densified wood. Previously, set-recovery has mainly been studied separately from other properties of densified wood, while in this work, set-recovery was also studied in relation to hardness. The results show that set-recovery was almost eliminated with TM 6 h in the case of CR 40 and 50 %. Hardness significantly increased due to densification and even doubled compared to non-densified samples with a CR of 50 %. Set-recovery reduced the hardness of densified (non-TM) wood back to the original level. TM maintained the hardness of densified wood at an increased level after set-recovery. However, some reduction in hardness was recorded even if set-recovery was almost eliminated. [ABSTRACT FROM AUTHOR]

Compression and relaxation properties of selected biomass for briquetting (barley, oat, canola and wheat straw) were investigated to determine the correlation with variables (pressure, particle size (hammer mill screen size) and moisture contents). The applied pressure ranged from 7.03 to 14.06 MPa. Three hammer mill screen sizes (19.05, 25.40 and 31.75 mm) were used to grind the biomass samples. The ground biomass materials were conditioned to moisture contents of 9%, 12% and 15% (w.b.). The results indicated that the compact density of biomass increased with increasing pressure and moisture content. The relaxation properties of selected materials were affected by the set variables. Biomass materials had a higher stress relaxation speed with higher applied pressure and lower moisture content. [ABSTRACT FROM AUTHOR]

In order to utilize the plantation poplar wood, white poplar boards were soaked, heated and compressed to improve the mechanical properties in this study. The densities and densified zones were managed inside the board by choosing various parameters of soaking time between 0.5 and 5.5 h, heating time between 20 and 200 s and pressing time between 6 and 60 s. The density gradient was generated with the higher density near surface and the lower density toward the center of board. With this method, the density near the surface can be modified to 0.89 g/cm with an increase of about 100 % in comparison with poplar wood without any treatment. The boundary between the high-density layer and the low-density layer was characterized by X-ray scanned images. The modulus of elasticity (MOE) of compressed white poplar wood increased linearly with the compression ratio, and the modulus of rupture (MOR) increased exponentially. At the compression ratio of 47 %, MOE and MOR of compressed poplar wood were 19.77 GPa and 153.94 MPa, respectively. They were 73.2 and 88.9 %, respectively, greater than that of untreated specimens. [ABSTRACT FROM AUTHOR]

The use of wood-based connectors as a possible substitute of metal fasteners, for specific applications, in modestly loaded and moderately dense timber components, in new timber assemblies as well as for restoration works, is discussed. The densification technique has been used to obtain a wood-based material with higher mechanical performance with respect to the natural wood. A dedicated research has been carried out to monitor the compression behaviour of the wooden nails. The progress of pushing force during insertion of the wooden nails into wood samples was analysed and served for insertion process control. 600 compression tests were carried out to evaluate the mechanical behaviour of densified wooden nails, obtained from four different hardwood species and with different densification ratios. Beech, densified at 0° ring angle, 60% densification ratio, was selected for the further experimental campaign on the joints. Ten push-out tests have been performed on timber-to-timber joints. Results in terms of rigidity, resistance and post-elastic behaviour are discussed. The observed variability (slip modulus CoV = 26.7%, maximum load CoV = 23.7%) is mainly dependent on the occurrence of geometric flaws during nail insertion. Ductility exhibited by a group of joints was given by nail embedding into the wood before failure as well as by the bending resistance of the nail. The choice of an optimized technology for wood densification and for nail insertion is considered as a key factor for the optimal employment of the novel connectors. [ABSTRACT FROM AUTHOR]

Dimensional changes in both non-densified and densified, thin, wooden components and layered materials after external pressing forces were released were evaluated in this work. Densification was carried out using a cold process on a semi-automatic hydraulic pressing machine. The specimens' dimensional stabilities, focusing mainly on their residual plastic deformations, were monitored. The impacts of several factors, such as wood species, material thickness, densification degree, and their combinations, were analyzed. Results showed that, with increased degree of densification, the relative plastic deformations (pressing degree) usually decreased. With regard to the compositions explored, the best combination was a top poplar layer densified by 10% plus a bottom beech layer densified by 20%. The impacts of each of the factors on the pressing degree values proved to be significant; the least significant was the bottom beech layer thickness and degree of densification. The greatest practical benefits can be obtained using the recommended combinations of composite layers. [ABSTRACT FROM AUTHOR]

A new approach to reinforce glulam timber beams using compressed wood (CW) has been developed by the Author. The compressed wood blocks are inserted into pre-cut holes on the top of glulam beams to produce pre-camber and to generate initial tensile and compressive stresses on the top and on the bottom extreme fiber of the glulam beam, respectively. A simple analytical approach has been developed to predict pre-camber deflections of the beams reinforced with three CW blocks. Assuming that moisture-dependent expansion of the CW block creates an interactive linear pressure between the glulam beam and the CW block, this would generate a pair of eccentric force away from the neutral axis of the beam. It is shown that the pre-camber deflection predicted at midspan of the short beams with various reinforcing arrangements give good agreement with the measured pre-camber from previous experimental results. [ABSTRACT FROM AUTHOR]

The aim of this work is to explore the potential application of chemically modified olive husk residue (OHR) as naturally occurring fillers to reinforce (Nylon-12) thermoplastic to produce a cost-effective wood like material. The Nylon-12/OHR composite material was fabricated via melt mixing of the Nylon-12 followed by the addition of chemically treated OHR at 180 and 50 rev. min-1 using Brabender internal mixer. The composites were characterized with respect to their dynamic mechanical properties, namely storage and viscous moduli (E, E) and mechanical loss factors (tan δ) using dynamic mechanical analyzer (DMA). The thermal stability of the samples with and without chemically treated OHR were examined using thermo-gravimetric analyzer (TGA). The chemical resistance of the composites was evaluated by immersing the samples in acidic and basic media and by exposing the samples to thermo-oxidative ageing (TOA) at 80C for 72h. The influence of TOA and immersion medium on the percentage weight loss, impact strength and hardness of the composites were reported. The effect of TOA and the solvent attack on the microstructure of the fractured samples was viewed by scanning electron microscope (SEM). [ABSTRACT FROM AUTHOR]

Transverse compression of wood is a process that induces large deformations. The process is dominated by elastic and plastic cell wall buckling. This work reports a numerical study of the transverse compression and densification of wood using a large-deformation, elastic-plastic constitutive law. The model is isotropic, formulated within the framework of hyperelasticity, and implemented in explicit material point method (MPM) software. The model was first validated for modeling of cellular materials by compression of an isotropic cellular model specimen. Next, it was used to model compression of wood by first validating use of isotropic, transverse plane properties for tangential compression of hardwood, and then by investigating both tangential and radial compression of softwood. Importantly, the discretization of wood specimens used MPM methods to reproduce accurately the complex morphology of wood anatomy for different species. The simulations have reproduced observations of stress-strain response during wood compression including details of inhomogeneous deformation caused by variations in wood anatomy. [ABSTRACT FROM AUTHOR]

Compression wood has undesirable properties for structural timber and for paper production. Traditional methods of detecting it are often time consuming and subjective. This study aimed to rapidly and impartially detect compression wood through the use of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and diffuse reflectance near infrared (NIR) spectroscopy. Compression wood and non-compression wood samples were obtained from young Pinus radiata D. Don trees grown in New Zealand. Longitudinal dimensional changes were measured during drying or water saturation of the samples; lignin and galactose contents were determined using conventional analytical techniques. Chemical composition was here a more reliable discriminator between wood types than longitudinal dimensional changes. It was shown that partial least-squares regression (PLS-R) or discriminatory analysis (PLS-DA) could be used to build models on the training samples that could discriminate between wood types of the independently grown validation samples. Ultimately, both types of spectroscopies could be used to discriminate between compression wood and non-compression wood either through prediction or discriminatory analysis with equal success. Investigation into spectral differences between wood types, including sequential mixtures of wood types, showed that for the mid-IR region absorbance at a well-resolved lignin band could be used to discriminate compression wood from non-compression wood. For NIR, a similar investigation showed that absorbance values at four separate wavenumbers or the 6000-5600 cm−1 region of the first derivative spectra were required for that discrimination. It is proposed that if there is a gradual change in the chemical composition of compression wood with its severity, then IR spectroscopy could feasibly be used to rapidly determine compression wood severity. [ABSTRACT FROM AUTHOR]

Scots pine ( Pinus sylvestris L.) wood was surface densified in its radial direction in an open press with one heated plate to obtain a higher density on the wood surface whilst retaining the overall thickness of the sample. This study investigated the effect of temperature (100, 150 and 200 °C) and press closing speed (5, 10 and 30 mm/min, giving closing times of 60, 30 and 10 s, respectively) on the micromorphology of the cell-wall, as well as changes occurring during set-recovery of the densified wood. The micromorphology was analysed using scanning electron microscopy (SEM) combined with a sample preparation technique based on ultraviolet-excimer laser ablation. Furthermore, the density profiles of the samples were measured. Low press temperature (100 °C) and short closing time (10 s) resulted in more deformation through the whole thickness, whilst increasing the temperature (150 and 200 °C) and prolonging the closing time (30 and 60 s) enabled more targeted deformation closer to the heated plate. The deformation occurred in the earlywood regions as curling and twisting of the radial cell-walls, however, no apparent cell-wall disruption or internal fracture was observed, even at low temperatures and fast press closing speed, nor after soaking and drying of the samples. In the SEM-analysis after soaking and drying, it was noticed that the cells did not completely recover their original form. Thus, part of the deformation was considered permanent perhaps due to viscoelastic flow and plastic deformation of the cell-wall components. [ABSTRACT FROM AUTHOR]