Volume 77, Issue 6

Wood is mainly subjected to transverse compression in many critical parts of Chinese traditional timber structures, e.g. the mortise-tenon and Dou-Gong joints. Seismic is one of the dynamic actions faced by these structures and will cause wood to suffer higher loading speeds than quasi-static loads. The investigation of the seismic strain rates (SSRs) effects of wood under perpendicular-to-grain compression (PTGc) is important. One hundred and forty-four radial small clear wood specimens were prepared using Dahurian larch, Mongolian pine and Chinese poplar. Monotonic and cyclic compression tests were conducted under three SSRs (10 −3  s −1 , 10 −2  s −1 , and 10 −1  s −1 ) and the quasi-static strain rate (10 −4  s −1 ). Failure modes, stress-strain curves, yield strengths, elastic moduli and the unloading/reloading moduli were analyzed. Results indicated that the PTGc properties were highly sensitive to SSRs under both the monotonic and cyclic compression. Strengths showed higher sensitivity to SSRs than elastic moduli. The SSRs effects of wood under cyclic compression have greater variability than the monotonic counterparts. The unloading/reloading moduli shows little SSR effects statistically. Comparisons were made between the existing PTG and the parallel-to-grain test results and a fitted general expression was obtained. Furthermore, an SSR-dependent stress-strain model was proposed and verified by tests.

Wood under thermo-mechanical densification behaves differently depending on the cross-sectional growth ring orientation (GRO) relative to the direction of compression. This influences the degree of cell damage, but also the shape-memory effects occurring when the compression load is released (spring-back) and when the timber is re-moistened (set-recovery). To study how the GRO influences the shape-memory effects, Scots pine specimens were separated into three distinct groups of GRO (Flat, Inclined, Hybrid) and then thermo-mechanically surface-densified. Spring-back and set-recovery were determined by thickness measurements and by digital image correlation. A GRO parallel to the densified surface, resulted in a low spring-back and a high set-recovery which were uniform over the width of the specimen. Specimens with a GRO between 15 and 45° to the densified surface showed high spring-back and low set-recovery, indicating cell-wall damage. Spring-back mainly occurred in the non-plasticised region immediately below the heated surface region and elasto-plastic rolling-shear deformation along individual growth rings occurred. The GRO of softwood subjected to thermo-mechanical densification determines if an applied load results in rolling shear-deformation or radial compression. This in turn determines where in the cross-section and when in the process the cells deform and if this deformation occurs below or above the glass-transition temperature.

Poor dimensional stability restricts the commercial utilization of fast-growing wood. In this study, fast-growing poplar ( Populus cathayana ) was treated by removing hemicellulose with hydrothermal treatment and impregnating alkali lignin via full-cell process, synergistically, for enhanced dimensional stability. After modification, hydroxyl groups were reduced in hemicellulose removed wood (DHC), alkali lignin was observed to fill in the cell lumens of vessels and wood fibers in the impregnated wood (AL) and in the wood modified by hemicellulose removal with alkali lignin impregnation (DHCAL). Compared with untreated wood, the volumetric swelling ratio of DHC and AL decreased by 11 % and 21 % under relative humidity (RH) of 89 %, respectively. The volumetric swelling ratio of DHCAL decreased by over 50 %, indicating a positive synergistic effect. The combination of hemicellulose removal and alkali lignin impregnation treatment improved the dimensional stability of wood significantly by reconstructing wood chemical components with various levels of hygroscopicity. This work could meaningfully contribute to the efficient utilization of fast-growing wood and promote the added value of industrial alkali lignin.

Degradation of the mechanical properties of heat-treated wood is a significant problem that needs to be addressed. This study aimed to stabilize the mechanical strength of heat-treated spruce wood by adding gaseous ammonia during the heat treatment. Gaseous ammonia penetrates rapidly into wood and is expected to form ammonium hydroxide when combined with water in the wood. This modification strategy neutralizes the acids produced by the degradation of hemicelluloses and reduces the degradation of the wood polymer composition and cell-wall structure. The preservation of wood polymer composition and cell-wall structure increases the indentation modulus of the wood cell walls. This increases the strength of the wood cell walls, resulting in an improvement in the mechanical properties of the heat-treated wood. The heat-treated wood’s dimensional stability and equilibrium moisture content are only slightly affected by the weak alkalinity modification.

This study aimed to evaluate the shape-memory effect (SME) of wood (Populus x beijingensis W. Y. Hsu) and identify the net-points and switches in its molecular and morphological structures. During several cycles of deformation and subsequent recovery, a high shape recovery rate and ratio were maintained. The transverse compression tests of wet and dry wood reveal that the hydrothermal coupling stimulation can considerably reduce the strength of wood. The X-ray diffraction characterization of wood under hydrothermal stimulation shows that the role of network nodes in the SME of wood is influenced by temperature. The wavenumber shifting and changes in the intensity ratio of the characteristic Fourier transform infrared peaks showed that hydrogen bonds acted as switches for the water-stimulated shape-memory behavior. By taking into account viscoelastic relaxation, a kinetic model derived from nonequilibrium thermodynamic fluctuation theory was used to describe the shape recovery process. The effects of hydration on recovery kinetics, activation, and dynamic mechanical behaviors were also studied. To explain the shape-memory mechanism of wood under hydrothermal stimulation, a hybrid-structure network model based on a single three-dimensional switch network was proposed in this study.

In this study, representative lignin samples differing in hydroxyl content, molecular weight, linkage composition and lignin units ratio were prepared from eucalyptus wood by different isolation means and modification means: milled wood lignin (MWL), kraft lignin classified at different pH (KL), lignocresol (LC), lignoresorcinol (LR), lignopyrogallol (LP) as well as lignocresol secondary functional switched samples (LC 2 nd deriv). The structure of various lignins was characterized in detail by Fourier transform infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR). In order to eliminate the interference of other factors, bovine serum albumin (BSA) with relatively simple protein structure and different kinds of lignin and their derivatives were selected as the research objects. The adsorption/desorption behavior and mechanism between lignin samples and BSA were studied by quartz crystal microbalance with dissipation monitoring (QCM-D). The results showed that the content of phenolic hydroxyl was the main factor affecting the interaction of lignin and BSA, but in addition, the molecular size, linkages composition and the types of lignin units also had important effects on its adsorption behavior. The research will provide theoretical guidance and all-round reliable basic data for the interaction of lignin on lignocellulose hydrolysis enzymes in industrial application.

The incorporation of nano-particles into coatings to protect wood against UV light has tremendous potential for improving coating performance. However, the understanding of the mechanisms by which these particles function on wood surfaces remains limited. The distribution and potential chemical interactions between alpha Fe 2 O 3 and wood were studied. The ability of different sizes of Fe 2 O 3 particles to intercept various wavelengths of light was assessed using ultraviolet/visible (UV–vis) spectroscopy using TiO 2 and ZnO particles for comparison. All particles intercepted UV light, but α-Fe 2 O 3 also intercepted a portion of the visible spectrum which might help explain its better performance. Scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDS) analysis of α-Fe 2 O 3 nano-particle distribution on different wood orientations of radiata pine ( Pinus radiata D. Don) and shining gum ( Eucalyptus nitens ) showed that iron particles were uniformly distributed on both pine and shining gum, but provided better UV protection to the more permeable radiata pine surfaces. Characterization of chemical interactions between α-Fe 2 O 3 and isolated lignin and cellulose by Fourier Transform Infrared Spectroscopy (FTIR) suggested substantial interactions between these particles and lignin components, but little interaction with cellulose. The results suggest that the role of nano-particles in the UV protection of wood surface is to intercept and disperse the light energy while interacting with the wood.

Variation in anatomical features of the culm wall namely the shape and size distributions of vascular bundles between different genera and species of bamboo is not well understood due to the cumbersome task of manual measurements. Using machine learning methodology, this work presents a universal vascular bundle detection model for rapid, reliable, and automatic characterization of vascular bundles in culm cross sections of 213 species across 23 genera of Chinese bamboos. The number of vascular bundles and the fiber sheath area have positive linear correlations with the outer circumference and the wall thickness, respectively. The distribution density of vascular bundles has a decay exponential correlation with the outer circumference and the wall thickness. The average fiber volume fraction was 35.2 % ± 7 % with relatively small variation between species. Bamboo species could be grouped into three categories based the endodermis to epidermis distribution pattern of radial and tangential length of vascular bundles, two categories of radial-to-tangential ratio and four categories of fiber sheath area distribution pattern. Implications on bamboo classification, structural and pulp/paper applications were discussed. The findings from this study provide groundwork for the establishment of a unified, authoritative and objective bamboo classification system based on the vascular tissue morphology.