Showing papers in "European Journal of Wood and Wood Products in 2018"

Liquid Deposition Modeling: a promising approach for 3D printing of wood

Abstract: Liquid Deposition Modeling is introduced as a promising technology for 3D printing of wood. Specimens were printed using different paste-like suspensions made from ground beech sawdust and methylcellulose dissolved in water. The wood content could be increased up to 89% in dry mass. Physical properties were influenced by binder/water ratio and wood particle size. Shrinkage due to drying was 17.3–20.0%. Density values (r12) lay between 0.33 and 0.48 g/cm3. Bending strength and modulus of elasticity ranged from 2.3 to 7.4 and from 284.8 to 733.1 N/mm2, respectively. Density, MOR and MOE increased with increasing viscosity of dissolved methylcellulose and decreased with increasing particle size.

Environmental aspects of material efficiency versus carbon storage in timber buildings

Abstract: This article highlights the interdependencies of carbon storage and material efficiency in timber buildings. These elements appear contradictory in regard to environmental factors. Following a general literature review of environmental aspects of timber buildings and their components, building elements are analyzed in regard to their relevance for both issues. Particular advantages for material efficiency and carbon storage in regard to specific building elements are discussed. The first section summarizes what currently qualifies as the state of art in environmental standards of timber buildings on building level, looking at influence on the sector and on the competition on wooden material for material or energetic use. Calculations on carbon storage of exemplary timber buildings are shown in the following section. A factor for material efficiency of wooden use is hereby introduced. The interdependencies of carbon storage and material efficiency are discussed on the level of building elements and according to necessary requirements. Results show that there is no “best” timber construction that fulfills all requirements, as each building and with that each specific construction needs to fulfill varying circumstances. It is thus demonstrated that it is not enough to only focus on one of the issues. It is important to keep these interconnections in mind for climate discussions in regard to timber buildings and to further optimize timber constructions and buildings to meet both targets.

Density and some mechanical properties of densified and heat post-treated Uludağ fir, linden and black poplar woods

Abstract: The effects of thermo-mechanical densification and heat post-treatment on air-dry density, modulus of elasticity (MOE), bending strength (MOR), and compression strength parallel to the grain (CS) of Uludag fir (Abies bornmulleriana Mattf.), linden (Tiliagrandifolia Ehrh.), and black poplar (Populus nigra L.) wood samples were investigated. Samples were densified with compression ratios of 25 and 50%, and at 100 and 140 °C. Then, the heat treatment was applied to the samples at 185 and 212 °C for 2 h. According to the results of the study, density of all wood samples increased together with the increase of compression ratio. Regarding compression temperature, the highest density increase was obtained at 100 °C. Mechanical strength (MOE, MOR, and CS) in densified samples increased depending on compression ratio and increase of density. The highest strength increase was in black poplar samples and the lowest was in linden samples. After heat post-treatment, mechanical strength of samples decreased depending on increase in treatment temperature. However, strength values (MOR except) of samples which are 50% compressed and heat-treated were found higher than control samples.

Prediction of equilibrium moisture content and specific gravity of heat treated wood by artificial neural networks

Abstract: In the present work, two artificial neural network (ANN) models were developed for modeling the effects of conditions of heat treatment process such as exposure period and temperature at equilibrium moisture content (EMC) and specific gravity (SG) at different relative humidity levels of heat treated Uludag fir (Abies bornmulleriana Mattf.) and hornbeam (Carpinus betulus L.) wood. A custom MATLAB application created with MATLAB codes and functions related to neural networks was used for the development of feed forward and back propagation multilayer ANN models. The prediction models having the best prediction performance were determined by means of statistical and graphical comparisons. The results show that the prediction models are practical, reliable and quite effective tools for predicting the EMC and SG characteristics of heat treated wood. Thus, this study presents a novel and alternative approach to the literature to optimize conditions of heat treatment process.

The impact of natural and artificial weathering on the visual, colour and structural changes of seven tropical woods

Abstract: This study investigates the effects of wood weathering on changes in its macroscopic and colour characteristics in connection with changes in its molecular and anatomical structure. Seven hardwoods suitable for outdoor architecture—bangkirai, cumaru, cumaru rosa, ipe, jatoba, kusia, and massaranduba—were exposed to the exterior out of ground contact for 1–36 months according to EN 927-3, and for 1–12 weeks in Xenotest with water spraying according to partly modified EN 927-6. With prolonged weathering, the following changes occurred in the top surfaces of all tropical woods: (1) visual—creation of longitudinal macro-cracks, (2) spectrophotometry and CIE-L ∗ a ∗ b ∗ —darkening in exterior exposure mainly due to pollutants, except for ipe, and vice versa lightening in Xenotest, as well as greening and blueing in both modes of exposure, (3) FTIR—faster decrease of guaiacyl than syringyl lignin, absolute decrease of conjugated and unconjugated carbonyl groups in the newly formed lignin-polysaccharide-extractive substrate in the photo-oxidized and washed-out cell walls, and decrease of cellulose crystallinity, (4) SEM—damaging of cell-walls by micro-cracks, and their degradation by thinning. Connections between changes of the individual characteristics of weathered woods, for example, between the colour (ΔE*, etc.) and the molecular structure (carbonyls, etc.), were also determined.

Synthesis, structure characterization and application of melamine–glyoxal adhesive resins

Abstract: To eliminate formaldehyde in melamine–formaldehyde (MF) resins the nonvolatile and nontoxic aldehyde glyoxal (G) was reacted with melamine to prepare novel melamine–glyoxal (MG) resins. These MG resins were synthesized with different M/G molar ratios, and their properties were tested. The liquid and hardened MG resins were characterized, and the oligomers formed and their distribution were determined by 13C NMR and matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS). The energy of activation of cross-linking of the MG resins was found to be higher than for MF resins. This rendered some applications possible, such as MG resins impregnated paper surface overlays and showed such resins limitations as binders for wood particleboard. The MG resins remained stable at ambient temperature for more than 12 days.

Chemical characterization of wood treated with a formulation based on propolis, caffeine and organosilanes

Abstract: The aim of the study was to present chemical characteristics of a potential wood protection system composed of three chemical components. The paper presents preliminary results of chemical and biological analysis of wood treated with a mixture of 30% ethanol extract of propolis, caffeine and organosilanes: methyltrimetoxysilane (MTMOS) and octyltriethoxysilane (OTEOS). The sapwood of Scots pine (Pinus sylvestris L.) was impregnated with the above mentioned solution by vacuum method. The samples of wood treated with preservative were subjected to accelerated aging procedure according to EN 84 and subsequently to mycological tests according to the modified EN 113. Structural analysis of the treated wood was performed using infrared spectroscopy FTIR. The concentration of silicon in wood samples was determined by atomic absorption spectrometry AAS. The percentage content of nitrogen in wood samples was determined by elementary analysis EA. Slight differences in nitrogen and silicon content recorded in wood samples following impregnation and leaching confirm the permanent character of bonding between the propolis-silane-caffeine preparation and wood. The stable character of Si–C and Si–O bonds was shown in IR spectra and discussed in detail in this paper.

The evaluation of panel bond quality and durability of hem-fir cross-laminated timber (CLT)

Abstract: To better use the second-growth wood resources in value-added applications, this work addressed the manufacturing aspects of cross-laminated timber (CLT) products from western hemlock (Tsuga heterophylla (Raf.) Sarg) and amabilis fir (Abies amabilis (Dougl.) Forbes) (or hem-fir) harvested from coastal British Columbia, Canada. Small CLT billets (nominal 610 mm × 610 mm) were made to examine CLT bond quality and durability through block shear and delamination tests. Two types of adhesives, single-component polyurethane (PUR) and emulsion polymer isocyanate (EPI) and two critical applied pressure parameters (0.28 and 0.83 MPa) were adopted to manufacture hem-fir CLT. It was found that the adhesive type and applied pressure significantly affected wood failure percentage (WFP) and delamination of hem-fir CLT. When PUR adhesive was used, CLT made at 0.83 MPa pressure yielded significantly higher WFP and lower delamination than that made at 0.28 MPa pressure. The results demonstrated that despite the fact that hem-fir lumber is not particularly specified in the current North American CLT standard, it could be used for manufacturing CLT with the required panel bond quality.

The properties of Moso bamboo heat-treated with silicon oil

Abstract: Bamboo is very vulnerable to mold fungi, which greatly limits its applications. In this paper, moso bamboo was heat-treated with silicon oil at temperatures of 160, 175, and 190 °C for a duration of 2 h. The physical–mechanical properties and mold resistance were investigated. The chemical action of silicon oil within bamboo was analyzed by FTIR spectroscopy on bamboo samples before and after the oil heat treatment. The results showed that the hygroscopicity and the dimensional stability of bamboo were effectively improved by the oil heat treatment. The MOR of oil heat-treated bamboo increased as it was treated at 165 and 175 °C due to the oil uptake, but its MOR decreased as the treated temperature increased to 190 °C; at this temperature the degradation of chemical components should be considered. Mold grew more slowly on the oil heat-treated bamboo than untreated bamboo, and the performance of mold resistance was also effectively improved. In addition, the presence and chemical action of silicon oil were also examined through a comparison of FTIR spectrum of untreated control and 175 °C oil heat-treated bamboo.

Bondline shear strength and wood failure of European and tropical hardwood glulams

Abstract: The study reports on block shear investigations with bondlines of face-glued laminations and matched solid wood specimens from hardwood glulam (GLT) beams produced industrially from eight technically and stand volume-wise important species. The European hardwoods comprised oak, beech, sweet chestnut and ash and the tropical species were teak, keruing, melangangai and light red meranti. The adhesives were phenol-resorcinol and melamine-urea. When combining all species in one sample, a rather strong linear relationship of bond and wood shear strength was observed. The ratio of bond vs. wood shear strength was for all species on the mean value level ≥ 0.9, and likewise (with one exception) for the respective strengths’ 5%-quantiles. Consistent with literature, the test results showed no significant correlations between bond shear strength and density, wood shear strength and wood failure percentage of individual species, respectively. The investigations render the methodological basics of some international standards on bond quality verification as being inappropriate. New, empirically validated hardwood GLT bond requirements are proposed for discussion and implementation at the CEN and ISO levels. The strength ratio specifications reflect respective ANSI provisions, yet the reference quantity wood shear strength is now determined in an unbiased manner from matched GLT specimens. The wood failure verification proposal is based on the 10%-quantile and mean level for initial type testing and factory production control. The requirements further account for the pronounced difference observed in scatter of wood failure between European and tropical species.

The status of chain-of-custody certification in the countries of Central and South Europe

Abstract: The significance of wood and paper products originating from certified sustainable sources has been increasing worldwide during the last two decades paralleling overall interest and concern for global sustainability issues. Forest certification is a voluntary verification tool that has been gaining importance not only as an independent verification tool in the wood processing industry but also as an influencer in private and public purchasing policies and as a component of emerging wood harvesting and trade legality schemes. There are two main types of certification, forest certification for forest management and chain-of-custody (CoC) certification which tracks certified wood through the manufacturing supply chain. This study focuses on the chain-of-custody component. A multinational survey of CoC certificate holders in Slovakia, Czech Republic, Poland, Slovenia, Croatia and Serbia was conducted to identify the general understanding of certification concepts as environmental, economic and social tools, to determine incentives for CoC certification implementation by companies, and to identify difficulties in existing certified wood product supply chains. Results indicate that respondents demonstrated a high level of understanding of the chain of custody certification concept. Respondents also link forest certification mainly to the issues of legality, tracing the origin source of supply and prevention from illegal logging. The main expected benefits are linked to the improvement of external company image followed by business performance factors such as penetrating new markets, increase of sales volume, expanded market share and the increase of profit margin. The key problems connected to certified supply chains relate to the overpricing of certified material inputs, while respondents reported none or minimum price premiums for their certified products over non-certified alternatives.

Life cycle assessment of product- and construction stage of prefabricated timber houses: a sector representative approach for Germany according to EN 15804, EN 15978 and EN 16485

Abstract: Energy savings in the use phase of a building’s life cycle increased the relative importance of environmental impacts of the product-, construction- and end-of-life stages of a building. The European Committee for Standardization (CEN) thus developed horizontal standards to enable the sustainability assessment of construction works over their entire life cycle. Consistent with the European standards EN 15804, EN 15978 and EN 16485, a life cycle assessment (LCA) was carried out to determine the environmental impacts of the production and construction stages of an average prefabricated timber house produced in Germany as well as its particular building elements (1 m² inner/outer wall, 1 m² roof element, 1 m² ceiling element). The life cycle inventories (LCIs) were compiled on the basis of annual data of 12 participating manufacturers of prefabricated timber houses. A specific LCA model was developed for the calculation of the input- and output flows referring to the functional units on factory level. Furthermore, one focus was laid on the application of the modular principle according to EN 15804/15978 to construction systems with a high level of prefabrication. The normalization to the overall German impacts shows that the contributions to the environmental categories global warming potential (GWP), acidification (AP) and to the abiotic depletion potential (ADPe) are most important. The highest impacts originate from the manufacturing of the building materials. However, for the categories GWP and AP, around 30% of the impacts originate from the prefabrication of the building elements, their transport and the processes at the construction site.

Fabrication of soybean protein-acrylate composite mini-emulsion toward wood adhesive.

Abstract: A series of soybean protein-acrylate composite mini-emulsions used for wood adhesive were facilely synthesized by mini-emulsion polymerization. The chemical compositions, properties and adhesive performances of composites were characterized by FTIR, SEM, TEM, TGA, DSC, XPS and bonding strength. The results indicated the copolymerized emulsions had appropriate particle sizes and uniform particle distribution. Soy protein could make active groups crosslinked with polyacrylate within or between molecules. The glass transition temperature (Tg) of acrylate was changed after adding soy protein. The binding energy of C (1 s) had a significant change. Besides, parts of C–O and C=O groups reacted to soybean protein and finally formed carboxyl groups. Bonding strengths of plywood prepared by mini-emulsion were all higher than 0.7 MPa, meeting the standard of GB/T9846-2004 II. The successful fabrication of soyprotein acrylate composite adhesives could open up a new way for wood adhesives with no release of free phenol nor free formaldehyde.

Assessment of polyphenol content and antioxidant activity of oak bark extracts

Abstract: Extraction efficiency of total polyphenols and flavonoids from bark oak (Quercus robur L.) grown in the central region of Poland was evaluated. The total phenolics of water and 60% ethanol and extracts were in the range of 55.4–60.4 and 71.0–79.3 mg gallic acid/g of bark, respectively, while the total flavonoid content in these extracts were determined in the range of 35.1–38.0 and 72.0–78.4 mg catechin/g. The hydroalcoholic extracts exhibited higher DPPH radical scavenging activity than BHT (butylated hydroxytoluene), popular food additives.

New insights into the psychological dimension of wood–human interaction

Abstract: The effect a wooden-built environment exerts on the physical and psychological well-being of people has mostly been investigated by evaluation, through a limited number of sensory modalities, of small size stimuli. In this research, two real-size wooden and plaster indoor settings were used to examine the influence of wood on people’s emotions and perceptions. Three questionnaires assessed participants’ multimodal sensory, affective, and cognitive responses to the settings (Semantic Differential questionnaire), their emotional state (Positive and Negative Affect Schedule), and their environmental behaviour and biophilia degree (Nature Relatedness Scale). The results revealed that wood induces more positive emotions than plaster, and that individual biophilia degree appears to influence the tactile, auditory, and olfactory evaluation of the settings. It furthermore indicates how wood used in real buildings positively influences human psychological well-being and highlights the importance of considering multiple sensory modalities when investigating wood–human interaction.

Effect of short-term thermomechanical densification of wood veneers on the properties of birch plywood

Abstract: In this study, the physical and mechanical properties of plywood panels made from pre-compressed birch (Betula verrucosa Ehrh.) veneer were evaluated. Veneer sheets underwent short-term thermo-mechanical (STTM) compression at temperatures of 150 or 180 °C and at pressures of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 or 3.5 MPa for a period of 1 min prior to adhesive being applied and pressed into panels using phenol formaldehyde adhesive at 100 g/m2 spread rate; this was one-third less than the adhesive spread used for the control panels (150 g/m2). The pressing pressure was 1.0 MPa, which was almost half of the pressure used for the control panels (1.8 MPa); and pressing time was 3 min, also half of the pressing time used for the control panels (6 min). The results showed that surface roughness of compressed veneer, water absorption and thickness swelling of plywood panels made from compressed veneer were significantly improved. The shear strength values of plywood panels made from compressed birch veneer even with reduced adhesive spread were higher than those of plywood panels made from uncompressed veneer. The findings in this study indicated that compression of birch veneer could be considered as an alternative to produce more eco-friendly (owing to smaller adhesive spread) value-added material with enhanced properties.

A non-contact method for the determination of fibre direction of European beech wood (Fagus sylvatica L.)

Abstract: This paper introduces a non-contact method for the identification, quantification, and documentation of fibre direction of European beech wood (Fagus sylvatica L.). The developed approach is based on an automated visual analysis of the spindle pattern formed by the medullary rays, also termed wood rays. Each spindle is identified by means of image analysis technique, its position and orientation is determined, and the fibre direction of discretised elements is calculated. The individual process steps necessary to obtain an estimate of the fibre direction of a board are explained using the examples of five different failure types. In all examples, the estimated fields of fibre direction are congruent with the actual fibre direction determined by means of (1) the orientation of all present shrinkage cracks, which are established indicators for the fibre direction in wood, and (2) the fracture pattern after tensile testing. Employing the presented approach could open up new possibilities for the characterisation of European beech and other hardwood species with multi-row medullary rays in several fields of application, in particular regarding stress grading.

Effects of recycled fiber content on the properties of medium density fiberboard

Abstract: The large global production quantity of medium-density fiberboard (MDF) creates equal quantities of waste MDF, which consequently requires research on the recycling of MDF. This work was conducted to study the effect of recycled fiber (RF) content on the recycling properties of MDF. After pretreating waste MDF, a refiner and hammer were used to isolate refiner RFs (RRFs) and hammer mill RFs (HRFs) from two softwood species. This work also characterized the physical, chemical, and morphological features of RFs and virgin fibers (VFs). RRF and HRF contents of 0, 5, 10, 20, 30, 50, and 100% were used to fabricate recycled MDF (rMDF) panels. All RFs had shorter fiber lengths and higher fines contents than VFs had. The presence of N from urea–formaldehyde resins was confirmed by multiple analyses; more N was distributed in RFs than in VFs. The highest internal bonding (IB) strength of the rMDF occurred at 10% RF, regardless of isolation method and wood species; IB strength decreased afterward. The mechanical properties, including modulus of rupture, modulus of elasticity, and screw withdrawal resistance of rMDF, showed behaviors similar to the IB strength with increasing RF content. However, the thickness swelling, water absorption, and formaldehyde emission of rMDF samples decreased with increasing RF content. Statistical analysis indicates that the minimum of 10% RFs can be used to replace VFs without diminishing the properties of rMDF. The improved properties of rMDF were ascribed to the reinforcing effects of RFs covered with cured resins.

Thin antimicrobial silver, copper or zinc containing SiOx films on wood polymer composites (WPC) applied by atmospheric pressure plasma chemical vapour deposition (APCVD) and sol–gel technology

Abstract: Microbial colonization of wood and wood polymer composites (WPC) by bacteria and mould can cause aesthetic damage, negative impact on mechanical properties or even health hazards. This work investigated the structural morphology, elemental composition and antimicrobial properties of thin functional silicon oxide films deposited on WPC using atmospheric pressure chemical vapour deposition (APCVD) and sol–gel technology. Scanning electron microscopy results indicated the creation of flat, thin and closed films on top of the surface of this material. By embedding of active agents such as silver, copper or zinc, the APCVD films became slightly rougher. The corresponding sol–gel-films showed a certain number of cracks. The elemental composition of the films was investigated by X-ray photoelectron spectroscopy and depth profiling indicating the integration of active agents into the created SiOx film matrices. Moreover, the possibility to generate combinations of active agents in one layer could be demonstrated. BacTiter-Glo® tests as a part of antibacterial investigations showed strong bactericidal properties for silver and copper as well as sufficient properties for zinc-containing layers against Escherichia coli. Antimycotic effects on mould strains Aspergillus niger, Paecilomyces variotii, Penicillium funiculosum and Trichoderma viride were low for films containing only one active agent. Significant improvements in activity were achieved by the combination of these active agents.

Chemical and anatomical characterization, and antioxidant properties of barks from 11 Eucalyptus species

Abstract: Bark is an interesting and available byproduct from the forest industry that can be used as biomass for biorefineries. The barks from 11 Eucalyptus species (E. botryoides, E. camaldulensis, E. globulus, E. grandis, E. maculata, E. ovata, E. propinqua, E. resinifera, E. rudis, E. saligna and E. viminalis) were studied for 4-year-old trees regarding their structural and chemical features, including the composition of ethanol–water extracts and their antioxidant properties. The bark of these young trees had a thin or inexistent rhytidome, with a reduced periderm with low suberized and lignified cells. The barks were structurally similar and characterized by a homogeneous phloem with little ray expansion and alterations in the collapsed phloem. Photomicrographs documented the main structural differences. There was a between-species variation in chemical composition: extractives ranged from 5.5 to 18.6% (the hydrophilic extractives were dominant) and lignin from 14.4 to 23.5%. The carbohydrates composition also showed between species variation, for example the glucose-to-xylose ratio ranged from 3.8 to 12.1, allowing to consider carbohydrate targeted utilizations. Suberin content was in all cases very low (< 1%). The between-species variation of the ethanol–water bark extracts was also high: total phenolics ranged from 283 to 917 mg GAE/g of extract, flavonoids from 121 to 387 mg CE/g of extract and tannins from 94 to 545 mg CE/g extract. The antioxidant activity ranged from 368 to 1042 mg Trolox/g of extract and IC50 values from 3.4 to 8.6 µg extract/ml (the value for trolox was 2.6). The bark extract of E. rudis was particularly interesting as regards its antioxidant capacity, as well as that of E. maculata and E. propinqua.

Modification of wood with formulations of phenolic resin and iron-tannin-complexes to improve material properties and expand colour variety

Abstract: European beech wood (Fagus sylvatica L.) was modified with thermosetting phenol–formaldehyde (PF) resins, which were blended with various additives (ferric chloride and a mixture of ferric sulphate and hydrolysable tannin) to stain the material. The aim was to stain the wood dark and to enhance the moisture-related properties as well as the weathering performance. The weight percent gain (WPG) and solution uptake were only slightly influenced by the composition of the resin formulations. All treatments induced high bulking, dimensional stability and reduced the maximum swelling of the wood. Particularly at high relative humidity the equilibrium moisture content (EMC) of the modified wood was clearly reduced compared to the control. All formulations darkened the wood colour and enhanced the colour stability. The formulations containing ferric sulphate and tannin caused the darkest colour and the highest colour stability in the course of weathering. The modification with all formulations clearly reduced the capillary water uptake compared to the control. The capillary water uptake increased due to weathering. The increase was highest with the control, followed by the samples modified with tannin formulations and those containing only PF as sole phenol component. It is concluded that addition of iron salt as well as tannin can be used to stain the wood dark without negatively affecting the effects of modification with PF resin.

Properties of wood treated with compound systems of paraffin wax emulsion and copper azole

Abstract: Wood is a natural and renewable material used extensively However, it is generally susceptible to biological attacks caused by fungi and termites Studies showed that copper azole (CA) could effectively inhibit the growth of such organisms CA belongs to water-borne preservatives and CA-treated wood inevitably suffers from poor dimensional stability In order to improve the water repellency of CA-treated wood, a paraffin wax emulsion was added to the CA preservative system at different ratios The compound systems were then used to treat Southern pine (Pinus spp) samples The basic properties of the compound systems, such as stability (storage stability and centrifugal stability), particle size and pH value, as well as the weight percent gains, contact angles, water repellency (water absorption, shrinkage and swelling) of treated samples were investigated The results are as follows: (1) the compound systems of CA and paraffin wax emulsion had a favorable miscibility, and their stabilities all reached level one (good stability); (2) compared with untreated wood, CA-treated samples showed poor water repellency, whereas samples treated with the compound systems indicated an obvious reduction in water absorption, and improved dimensional stability as well

Fabrication and characterization of HDPE resins as adhesives in plywood

Abstract: Demand has been growing for plywood utilizing novel formaldehyde-free wood adhesives which are more durable and require environmental protection and sustainable development during the service life. In this study, a series of HDPE film as novel adhesives in plywood due to many advantages are fabricated using hot-press process followed by cold-press process. The effects of moisture content, HDPE dosage, hot-press temperature and pressure at different levels on physical–mechanical properties were evaluated by tensile shear strength, compression ratio, water absorption and thickness swelling. The results indicated that HDPE film can independently be used as adhesive in plywood, meeting the requirement for type II grade plywood of GB/T 9846.3 (Plywood-part 3: General specification for plywood for general use. Chinese National Committee for standardization, 2004) and opening up a new way for formaldehyde-free adhesives in plywood used as interior grade. Moreover, analysis of variance showed that the most important effect factor on tensile shear strength and water absorption is HDPE layer; on compression ratio and thickness swelling it is moisture content of veneer. To study the optimal hot-press condition, optimization of preparation process for plywood was carried out by response surface methodology analysis (RSMA), and then analysis by Design-Expert software. The simulation results of tensile shear strength were validated by experimental findings, indicating that RSMA can be used as an effective method to predict optimal fabrication condition.

Combined effect of acetylation and heat treatment on the physical, mechanical and biological behavior of jack pine (Pinus banksiana) wood

Abstract: A comparative study on the combined effect of heat treatment and acetylation on jack pine wood properties was undertaken and the results were compared with those of each treatment carried out individually. The dimensional stability and mechanical property of wood with different treatments were examined and statistically analyzed. The results demonstrated that combined acetylation of jack pine wood with acetic anhydride and heat treatment at 190 °C has a positive effect on the dimensional stability. Results also suggested that the dimensional stability was affected more than the modulus of rupture (MOR) and modulus of elasticity (MOE) by both heat and acetylation treatments under the experimental conditions used. In addition, the hardness increases after high temperature modification but decreases slightly after acetylation. A comprehensive investigation of the effects of heat treatment and acetylation separately and together (combination treatment) on the fungal durability of jack pine wood against a brown rot fungus, Poria placenta (pp), and a white rot fungus, Trametes versicolor (tv) has also been performed. The results indicated that the weight loss caused by fungi is reduced by both modifications. It was also found that combination of heat treatment and acetylation offers additional bioprotection. FTIR results indicated that the heat and acetylation treatments have a significant influence on the chemical properties, but less influence on their structures.

Properties of particleboard produced from post-industrial UF- and PF-bonded plywood

Abstract: An approach based on the recycling of waste plywood as a recovered wood resource for the particleboard industry is described. It is demonstrated that post-industrial urea- (UF) and phenol-formaldehyde (PF) bonded plywood can be effectively shredded to the form of the recovered particles that can be a valuable material in particleboard manufacturing. The effects of shredding conditions and binder type on the recovered particles characteristics and the mechanical properties of the particleboards were analyzed. It is shown that the substitution of 20–100% of virgin particles with the recovered material is possible without affecting the performance of the particleboard.

Improving the physical and mechanical properties of particleboards made from urea–glyoxal resin by addition of pMDI

Abstract: The effect of pMDI on physical and mechanical properties of the particleboards made from urea–glyoxal resin was investigated. The nontoxic and ecofriendly urea–glyoxal (UG) resin was synthesized under weak acid conditions, and its different properties were measured. Then, pMDI at various contents (4, 6 and 8% on resin solids) was added to the UG resin prepared. The thermal and physicochemical properties of the resins prepared as well as their water absorption, flexural properties (flexural modulus and strength) and internal bond (IB) strength of the particleboard panels bonded with them were measured according to standard methods. According to the physicochemical results obtained, the addition of pMDI significantly accelerated the gel time and increased the viscosity and solids content of UG resins. Differential scanning calorimetry indicated that the addition of pMDI decreases the onset and curing temperatures of the UG resin. Physical analysis results of the panels indicated that the particleboards made from UG resins with isocyanate yielded lower water absorption when compared to those bonded with the control UG resins. Based on the findings of this research work, the mechanical properties of particleboard panels bonded with UG resins could be significantly enhanced by the addition of increasing percentages of pMDI. The panels having 8 wt% pMDI exhibited the highest flexural modulus, flexural strength and IB strength value and the lowest water absorption among all the panels prepared.

Microwave treatment of Eucalyptus macrorhyncha timber for reducing drying defects and its impact on physical and mechanical wood properties

Abstract: Microwave is a useful and proven tool for increasing permeability of refractory wood and, thereby, it can be used for reducing drying time and defects. However, strength loss is always a concern. In this study, green timber boards were treated with microwave in two intensities, low microwave (LMW), 89 kWh/m3, and high microwave (HMW), 95 kWh/m3, and compared with control boards. Samples of all three treatments were kiln dried together. Density and selected mechanical properties were also assessed after drying. LMW, the treatment which presented the best results, showed reduction in some drying defects, such as collapse (20%), surface check length (84%), internal check length (50%) and internal check width (70%). Density, MOE and MOR on static bending were unchanged, whereas reductions in shear strength (13%) and compression strength parallel to grain (10%) were observed. HMW, on the other hand, produced higher strength reductions and more drying defects than LMW. Fine adjustments of LMW microwave power might bring drying benefits without strength losses.

Dynamic mechanical analysis and creep-recovery behavior of agglomerated cork

Abstract: The mechanical behavior of agglomerated cork, made of cork granules bound with polyurethane moisture-cured adhesive is investigated and compared to natural cork in the small strain regime (strain <5%). Dynamic mechanical analysis (DMA) of the agglomerated material revealed two distinct thermal transitions, one at −45 °C, related to the glass transition of polyurethane, and one at 3 °C, associated with melting of suberin, a natural polyester that is the main component of cork’s cell walls. Natural cork showed the latter transition to occur at a higher temperature range, between 10 and 25 °C, probably due to a different crystalline arrangement being formed upon cooling the cork granules under pressure in the mold. The storage modulus of agglomerated cork was found to be similar to that of natural cork. Creep and recovery experiments were well described by Burgers model and Weibull distribution function, respectively. Agglomerated cork showed higher instantaneous creep strain and viscous flow than natural cork, probably due to relative displacement and slippage of the granules being allowed by the binder. In all cork materials, not all the instantaneous creep strain was instantaneously recovered. A fraction underwent delayed recovery and another turned into permanent strain. This behavior was associated with the deformation of corrugations in the cork cell walls. Cyclic creep-recovery tests showed for all cork materials recoveries above 90%, except for the first cycle.

Strength degradation and service life prediction of timber in ancient Tibetan building

Abstract: Tibetan heritage building has attracted much attention recently for its historical and cultural value. Many of these buildings have different degree of damage after hundreds of years of service. A multivariate cumulative damage (CD) model and prediction model of strength degradation of timber in the ancient Tibetan building are proposed in this study. Experimental tests on old and new timber are conducted and a correction factor considering the effects of different influencing factors on the timber properties is introduced to modify the strength prediction model. Two failure criteria based on the ultimate strength capacity and allowable deformation are proposed to predict the service life of timber component. Finally, reliability-based analysis is conducted for the residual strength and service life prediction of timber component with consideration of the statistical uncertainty of different influencing factors. The analysed results show that the rate of residual strength degradation increases with time with consideration of different influencing factors. An ancient timber component with a longer history associates with a lower reliability.

Ligneous resole adhesives for exterior-grade plywood

Abstract: The performance of lignin–phenol–formaldehyde (LPF) resole adhesives was investigated for exterior-grade plywood manufacture using commercial pine kraft lignin to replace 40 wt% of phenol. Furthermore, the implementation of a lignin methylolation step prior to resole cooking was tested aiming to activate lignin towards the electrophilic aromatic addition of formaldehyde and to improve thus the performance of the respective adhesive. Comprehensive monitoring of the resole cooking process and characterization of the obtained resins confirmed a significant network expanding effect of lignin. This is evident from the fast increase of viscosity which occurs, however, at the expense of cross-link density, as reflected by the somewhat longer B-time measured for both types of ligneous PF resins. Evaluation of bonding strength development using a bond strength development test confirmed that the less dense network of LPF resins translates into delayed bond formation compared to the PF reference resin. Methylolation of lignin prior to resole cooking had no significant impact on bond formation as evident from the very similar behaviour during the bond strength development test. However, both the studied LPF resins turned out to be suitable adhesives for the manufacture of plywood panels for outdoor usage. Specimen prepared from beech veneers fulfilled the respective standards as determined by shear strength and bending strength tests.