Volume 76, Issue 8

Wood is increasingly viewed as a more environmentally sustainable material owing to its low embodied energy, workability, and renewability, but its two major drawbacks are susceptibility to biological degradation and fire. Biodegradation is typically addressed through effective designs to exclude moisture or, where that is not possible, the use of either naturally durable or chemically protected timber. Naturally durable timbers are widely used globally while preservative treatments are increasingly used to protect less durable timbers. These practices have markedly extended the use and service life of timber in harsher environments. However, these treatments do not improve the fire performance of the timber and there is increasing interest in the use of fire resistive coatings or impregnation with fire retardants to allow use in bushfire prone areas. This review provides background on the problems associated with increased building and construction in the wildland-urban interface. It summarizes the codes, standards and state of the art practices needed for adequate fire safety in timber construction.

Substantial efforts have been undertaken for visualizing and simulating the characteristics of water movement in wood. However, three-dimensional (3D) thermo-hygric simulations still pose challenges, not only because wood has a heterogeneous microstructure that results in complex computational models but also because there is a lack of proper experimental techniques to support and validate the model constructions. In this study, the moisture distribution in wood during the water adsorption and desorption processes was first visualized using a near-infrared hyperspectral imaging (NIR–HSI) method that has high resolution, sensibility, and stability. Then, based on the moisture visualization results, the main parameters of a mass transfer simulation code were varied. The visualization and simulation results were confirmed to match well with the main characteristics; e.g., drying speed was slower in the wood parts with higher densities. Additionally, there was a relatively large gradient over the surface layer of the wood samples as the drying progressed, whereas this was not an obvious feature in the water adsorption process. Hence, this study proposes that the NIR–HSI method can be combined with thermo-hygric and 3D simulation model construction. Such an approach provides the basis for optimizing drying conditions and providing high-quality wood products.

The moisture adsorption/desorption and swelling/shrinkage behavior of Catalpa bungei wood samples were documented in real-time at a mesoscopic scale using dynamic vapor sorption resolution combined with a Dino X Lite Digital Microscope. The results showed that earlywood, latewood, and growth ring samples exhibited varying water vapor sorption isotherms and hysteresis degrees throughout all relative humidity (RH) levels. The radial swelling/shrinkage strains in the separated earlywood (EW) and the growth ring earlywood (GR-E) were lower than that in separated latewood (LW) and growth ring latewood (GR-L) regions. The growth ring region (GR) containing earlywood and latewood tissues , presented an intermediate strain behavior. In contrast, GR-E’s swelling/shrinkage strains resemble LW, GR-L, and GR in the tangential direction. In particular, the GR swelling/shrinkage behavior resembled that of latewood regions, and GR-L had maximum swelling/shrinkage strains. This means that latewood dominated the swelling/shrinkage of the growth ring, promoted to a certain extent by earlywood. Strain hysteresis was observed when the swelling/shrinkage strain was considered an RH function. Latewood regions (LW, GR-L) showed more pronounced swelling hysteresis than earlywood regions (EW, GR-E) in the tangential and radial directions. Furthermore, at any relative humidity the change of the size of the specimen was immediately stabilized when the moisture content reached its equilibrium.

This study aimed to clarify the effect of different solvents, aqueous 1,4-dioxane, ethanol, or ethylene glycol at various mol%, on the formation rate of the benzyl cation, which forms via two steps, the protonation of the benzyl hydroxy or alkoxy group as a pre-equilibrium step and subsequent liberation of the water or corresponding alcohol molecule, respectively, in a model system of the lignin acidolysis, focusing on distinguishing the effects on both steps. For this aim, the acidolysis reactions were conducted in various aqueous solutions and organic solvents that showed a specific proton activity to establish the pre-equilibrium at a specific position. The formation rate of the benzyl cation showed minima in the intermediate mol% range. However, these rate differences were much smaller than those observed in the previous report where the aqueous solutions were prepared to contain a specific acid concentration and show different proton activities and thus the net effect of the solvent type on both steps was indistinguishable. These results clearly showed that the solvent type affects the first step (the proton activity) much more than the last step (the solvent-dissociating power). This paper also describes the preparation of the aqueous solutions to demonstrate a specific proton activity.

The improvement of wood decay resistance is more inclined to eco-friendly methods such as the application of natural products, but the low durability of some natural products as wood preservatives limits their applications. In this study, vanillin catalyzed by laccase was grafted into poplar wood to increase wood decay resistance and can remain in wood for longer period. The reaction system of vanillin, ABTS, laccase and phosphate buffer solution was impregnated into poplar wood using vacuum-pressure method, and reacted at 40 °C for 6 h. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR) were used to confirm the grafting reaction actually occurring during the process. The decay resistance, leaching resistance and mechanical strength of grafted wood were evaluated. Energy-dispersive X-ray (EDX) mapping was used to characterize the vanillin distribution. The results indicated that vanillin grafted poplar wood had good decay resistance, leaching resistance and higher strength. The mass loss of grafted poplar wood exposed to white-rot fungi [ Trametes versicolor (L. ex Fr.) Quél.] and brown-rot fungi [ Gloeophyllum trabeum (Pers.: Fr.) Murr.] decreased from original 46 and 13% to 9 and 4%, respectively, even after leaching. The modulus of rupture (MOR) and modulus of elasticity (MOE) of the grafted poplar were 11 and 26% stronger than original poplar wood. Vanillin was found in wood cell wall. It was actually esterified onto wood catalyzed by the laccase.

Scots pine sapwood ( Pinus sylvestris L.) was impregnated with different concentrations of capric acid (CA) (20, 40, 60 and 80%) as phase change material (PCM). The hygroscopic, mechanical properties and thermal energy storage (TES) characteristics of the CA-impregnated wood were studied. The morphology, crystalline properties, phase change properties and thermo-regulative performance of CA-impregnated wood were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), thermogravimetry (TGA), differential scanning calorimetry (DSC) and thermal performance analysis. CA-impregnated wood demonstrated an excellent performance of storing and releasing heat during phase change process, confirmed by DSC and FTIR analysis after an accelerated thermal cycling test. In addition, the accelerated thermal cycling test results indicated that CA-impregnated wood showed good thermal reliability and CA did not leach from the wood after the thermal cycling. Wood impregnated with CA solution of 80% concentration reduced the maximum temperature by 4.04 °C at the end of the heating period while it increased the minimum temperature by 2.83 °C at the end of the cooling period. The performance of storing and releasing heat during phase change process of CA impregnated Scots pine proves that it can be used as a thermal regulating building material to reduce energy consumption and cost caused by day and night temperature fluctuations.

The efficient conversion of bamboo biomass into biofuel and biomaterials as well as other chemical treatments are strongly related to the porosity of its cell wall. The present work characterizes the micropore and mesopore structure in the cell walls of six bamboo species using both CO 2 and N 2 adsorption methods. For comparison, two plantation wood species were also tested. As a whole, the tested bamboo species showed lower cell wall porosity (2.6%–3.8%) than wood species (4.0%–5.1%), indicating a more compact cell wall structure for bamboo than wood. Furthermore, the cell wall pore structure and porosity were shown to be tissue-specific, taking Moso bamboo ( Phyllostachys eduli ) for example, the parenchyma cells exhibited higher pore volume and porosity compared to the fibers. The obtained results provided additional explanations for the higher biomass recalcitrance of bamboo and bamboo fibers as compared to wood and parenchyma cells, with respect to cell wall pore structure.

Engineered bamboo products have been increasingly used in construction. However, there are few studies on its shear performance. Thus, the shear properties of bamboo lamina strips were investigated by the Iosipescu shear test. This study aimed to obtain the shear stress-strain curves and the lamina’s corresponding strength and modulus values, which can be used to design and model bamboo structural components. With this goal, 120 specimens were tested, considering the effect of loading directions on bamboo fiber, the existence of bamboo nodes, standard thickness, and fiber volume fraction. The characteristic shear strength values were also estimated based on the test data. Results show that the bamboo nodes and standard thickness have a negligible effect on the shear modulus and strength values. In contrast, the shear properties were determined by the loading directions and fiber volume fraction. The specimens’ measured shear strength and modulus loaded parallel/perpendicular to the bamboo fiber direction were about 10 MPa/15 MPa and 550 MPa/1000 MPa. The fiber and matrix-dominate failure modes were noticed for the specimens, and the unidirectional bio-fiber reinforced composite theoretical model could be used to predict the modulus values of fiber-dominate samples based on the measured volume fraction of the fiber.