Volume 75, Issue 6

This study applied synchrotron radiation XRD to analyze the mechanical behavior of cellulose microfibrils in wood containing annual rings (thickness: 5 mm), for different layers of the secondary cell wall, under uniaxial load. Cellulose in S 2 and in S 1 and S 3 layers were analyzed respectively, and the data were used to investigate for deformation behavior in the lattice spacing ( d 004 ). As a result, the mechanical behavior of cellulose sometimes differed from the behavior of bulk wood. The rigidity of cellulose in the S 2 layer was larger than in S 1 and S 3 layers under both of tensile and compressive loads. However, once standardized with respect to estimated cellulose amount, this standardized rigidity was comparable across all layers and loading conditions. Variation in microfibril angle (MFA) and lattice spacing ( d 004 ) of cellulose barely changed at all under compressive load. Under tensile loads, there were both of positive and negative changes in MFA variation in both S 2 layer and S 1 and S 3 layers, while d 004 variation had little changes in almost all cases.

Basic density is a fundamental wood property of pulp and sawn wood. An IML Resi PD 400 drilling resistance tool (IML System GmbH, Wiesloch, Germany) was used to evaluate the basic density of Eucalyptus nitens discs and the impact of needle friction on basic density prediction. To determine the accuracy of that prediction with the commonly used linear drill bit shaft friction correction and determine whether this correction is linear, 40 discs were drilled radially, then cut into segments which were measured for basic density. Drilling resistance had a strong relationship with basic density in the outer wood; it was weaker at the pith but this did not compromise prediction accuracy. When using a linear friction correction, the drilling resistance underpredicts basic density by 7.6% in the first 2–3 cm after stem entry, after which the prediction error ranged from 0.6–1.9%. The friction correction was found to be nonlinear, especially at the first few centimeters. To apply this friction correction, basic density values from the model should be added to predict basic density values until 2.9 cm from Resi entry point and after that subtracted to account for the drill bit shaft friction.

This paper examines how the moisture conditioning method affects the electrical conductance of wood. A widely used dataset was acquired by Stamm in 1929 who used a method of conditioning where water-saturated wood specimens were partially dried, sealed and left for a period of time for moisture to be redistributed before the electrical conductance was measured. However, more recent measurements combined conditioning above saturated salt solutions and pressure plate/pressure membrane techniques to obtain equilibrium moisture contents at constant relative humidity levels in the full moisture range. In this paper, the electrical conductance as a function of moisture content was compared for these two conditioning methods. When the specimens were conditioned to constant relative humidity levels, the data obeyed a percolation model better than when the conditioning procedure by Stamm was used. This was attributed to that Stamm’s method gives moisture gradients through the specimen because of sorption hysteresis effects, even though the wood is conditioned to a steady-state moisture content. Equilibration to constant relative humidity levels thus provided more well-defined moisture states and that the data followed a percolation model indicates that the mechanism of electrical conduction in wood does not change, even at high moisture contents.

A 3D combined elastic-plastic damage constitutive model for wood is proposed within the theoretical framework of classical plasticity and continuum damage mechanics (CDM). The model is able to describe the various behavior of wood under loading, including the orthotropic elasticity, strengths inequality under tension and compression in each orthotropic direction, ductile softening under longitudinal compression, brittle failure under transverse tension, and parallel shearing, densification hardening under transverse compression. Hoffman criterion and a set of eight separate failure criteria were used to define wood yielding and damage initiation, respectively. Isotropic hardening was assumed after yielding and defined by an exponential type function. The constitutive model was implicitly discretized using backward Euler method, solved through the return mapping algorithm and implemented into ABAQUS through the user-defined material subroutine (UMAT). The proposed model was firstly verified by material property tests considering different stress states: monotonic and repeated tension and compression (in both parallel and perpendicular-to-grain directions), parallel-to-grain shearing, and the interactions between perpendicular-to-grain compression/tension and parallel-to-grain shearing, etc. Mechanical behavior of typical structural elements was further simulated to validate the proposed constitutive model.

In this work, a novel waterborne hyperbranched polyacrylate (HBPA) dispersed organo-montmorillonite (OMMT) emulsion was synthesized and used for the treatment of wood in a vacuum environment in order to enhance the physical and mechanical properties of the wood. The sapwood of Cathay poplar ( Populus cathayana Rehd.) and Radiata pine ( Pinus radiata D.Don) were used as the samples for experimentation. The results showed that the physical and mechanical properties of the wood improved significantly due to the successful penetration of the OMMT and HBPA into the wood cell wall. From it was also observed that OMET completely exfoliated from the HBPA matrix and formed a hydrophobic film covering on the inside walls of the cell lumen. Further, it was observed that the poplar sample displayed better mechanical properties than the pine sample because the pine has a more compact structure when compared to poplar and contains rosin. Furthermore, it was also observed that the mechanical properties of the modified wood sample gradually improved with an increase in the concentration of the emulsion. However, excessive concentration (>4 wt%) did not lead to further improvement.

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.

The effectiveness of pressurized hot-water extraction conditions for obtaining galactoglucomannans (GGMs) from Pinus halepensis suitable for applications like coatings and films packaging was investigated. For this purpose, high molar masses with high yields are required, presenting a serious challenge for hot-water extraction processes. The extraction of GGMs was carried out in an accelerated solvent extractor (ASE) and the isolation was performed by precipitation in ethanol. Three temperatures in the range 160–180 °C and five extraction times 5–90 min were tested in order to optimize extraction parameters of GGMs, avoiding thermal and chemical degradation in hot-water. Total dissolved solids (TDS) were determined gravimetrically after freeze-drying and weight average molar masses (M w ) were determined by high-performance size exclusion chromatography (HPSEC). Total non-cellulosic carbohydrates were determined by gas chromatography (GC) after acid methanolysis. Free monomers were additionally analyzed by GC. Lignin in water extracts was measured by an ultraviolet (UV) method. Acetic acid was determined after alkaline hydrolysis of acetyl groups and analyzed by HPSEC. The main parameters influencing the extraction processes of the GGMs, namely, extraction time and temperature were studied. Optimal extraction parameters of GGMs were identified at 170 °C and 20 min extraction time, with average M w of extracted fraction of 7 kDa leading to a GGM yield of approximately 56 mg go.d.m−1${\text{mgg}}_{\text{o}.\text{d}.\text{m}}^{-1}$, corresponding to 6% on dry wood basis.

Treating wood with water-soluble resins is a well-known and effective method to improve the durability of wood. However, there has been no systematic work to date related to the influence of average molecular size of phenol-formaldehyde (PF) resin on the decay resistance of wood, especially of hardwoods. Therefore, the goal of this study was to investigate the effect of average molecular size of PF resin treatment on the resistance of beech wood against brown- and white-rot fungi. Four different average molecular weights ( M w ) of resol type resin oligomers (297, 421, 655 and 854 g/mol) were examined. Different weight percent gains (WPGs) in European beech ( Fagus sylvatica ) wood blocks (15 × 20 × 50 mm 3 ) were attained through vacuum impregnation using various concentrations of aqueous-PF solutions. Afterwards treated wood blocks passed the leaching and were exposed to brown-rot fungi ( Gloeophyllum trabeum ; Coniophora puteana ) and white-rot fungi ( Trametes versicolor ) for 16 weeks. No effect of oligomer size on the resistance against G. trabeum decay of wood blocks was observed, resulting in resin loadings of 7–8%. The required WPG for resistance to brown-rot decay by C. puteana increased slightly with increasing oligomer molecular size: 6, 7, 10 and 11% for wood treated with 297, 421, 655 and 854 g/mol, respectively. The extent of white-rot fungal decay resistance of treated wood was affected by the molecular size of oligomers. Resin loadings of 8% and of 17% against T. versicolor were required to attain similar durability levels for beech wood treated with M w  = 297 and 854 g/mol, respectively.

Polyolefins used in building materials and furniture require the use of flame-retardant (FR) additives to improve their fire safety. Such additives should be safe to humans and the environment, and preferably bio-based. In the present work, the FR performance of unmodified and chemically modified technical lignins was compared to that of the ammonium polyphosphate/pentaerythritol (APP/PER) intumescent system in a polypropylene (PP) matrix. Micro-scale combustion calorimetry (MCC) was used to study the peak heat release rate (PHR), temperature at PHR (T PHR ), total heat release (THR) and char yield upon thermal decomposition of milligram-scale specimens. The PP/lignin composites showed up to 41% lower PHR and up to 36% lower THR compared to pure PP as well as large char residues. Based on the same parameters, especially the PP/lignin composites made with modified lignins outperformed the reference PP/APP/PER system and the PP/APP/lignin composites where unmodified lignin was used with APP. The most promising PP/lignin composites were prepared with partially demethylated/demethoxylated and depolymerised kraft lignin (‘CatLignin’), modified by the Mannich reaction to a nitrogen content of 13.5%.