Advances in Preparation and Modification of Wood-Based Materials

This study investigated the effects of adhesive resination and bamboo strand content on the physical and mechanical properties of thick Bamboo-Wood-oriented strand board (BWOSB), such as the air dry density (ADD), internal bond strength (IB), water absorption thickness swelling (TS), modulus of rupture (MOR), modulus of elasticity (MOE), and gluing properties. The raw materials used included large strands prepared from Chinese fir (Cunninghamia lanceolata), bamboo (Phyllostachys edulis), and modified isocyanate resin (PMDI). In this study, BWOSB specimens with different adhesive resination and bamboo strand content were fabricated, and their physical–mechanical properties were examined. It was found that the physical and mechanical properties of BWOSB with 8% PMDI resination were better than those with 5%, and their gluing damage was mostly in the form of the tearing of the raised vascular bundles of bamboo strands and the wood-breaking damage of wood strands. With the increase in the proportion of bamboo strands, the internal bonding strength and the short-span shear strength of BWOSB showed a tendency to decrease at first and then increase. The swelling rate of the water absorption thickness showed a tendency to decrease, and the other properties of BWOSB did not show a clear correlation with the change in the proportion of bamboo strands. The unique gluing interface between the bamboo and wood strands, which either used the “keyway” type of gluing effect or the “nail” type of gluing effect, determined the gluing performance of BWOSB, and the proportion of bamboo and wood strands influenced the gluing interface and gluing type of BWOSB, which ultimately affected the gluing performance of BWOSBs. The proportion of bamboo and wood strands also affected the gluing properties of BWOSBs by influencing the gluing interface and gluing type. This study provides a reference for the development of the production process of thick BWOSB and its application in the field of heavy load construction. Full article

Wood industries use thermal and thermomechanical treatments as ecological approaches to increase the durability of wood products, avoiding the need for chemical additives. In this regard, the aim of this study was to compare the physical and mechanical properties of plywood made from veneers treated at different temperatures using thermal and thermomechanical processes, with untreated panels serving as a control. The treatment process involved Pinus taeda veneers submitted to treatment in a hot press at 1.0 MPa in a laboratory oven at temperatures of 160 °C, 180 °C, and 200 °C for 30 min. For bonding the veneers, a vegetable-based polyurethane resin derived from castor oil with a grammage of 395 g/m² was used, applying pressing conditions at 90 °C, 0.6 MPa, and 10 min. Our results indicate that temperature significantly influences plywood properties, playing a key role in the choice of equipment for the treatment process. Regardless of the method employed, the treatment resulted in an improvement in the hydrophobicity of the veneers due to the decrease in hemicellulose content. Notably, the reduction in strength and stiffness caused by the loss of cell wall polymers was not statistically significant. The treatment was successful in softening the wood material, reducing roughness, and increasing wettability. Despite a minimum of 20% reduction in glue line tension, the samples still surpassed the 1 MPa mark, showing satisfactory results. This demonstrates the feasibility of adjusting treatment variables to ensure the proper use of this adhesive. Full article

The shortage of wood resources and the policy of logging restrictions have hindered the development of the wood industry. The development of fast-growing wood can effectively solve the problem of wood shortages and the discrepancy between supply and demand; however, the softness and poor strength of fast-growing wood make it difficult to use directly and restrict its applications. Meanwhile, the inflammability of wood is also a crucial hindrance to its application. In this work, hybrid wood composites with high strength and excellent fire retardance were developed by using a combined strategy of “delignification–mineralization–densification”. Delignification promoted the deposition of minerals inside the wood, and the mineralization process was able to significantly increase the fire retardance performance of the hybrid wood. The densification treatment made the wood and minerals closely packed, which was conducive to the improvement of the strength and fire retardance performance of the hybrid wood. The resulting hybrid wood composites showed enhanced mechanical strength (the tensile strength, flexural strength, and compressive strength were 180.6 MPa, 159.8 MPa, and 86.5 MPa, respectively) and outstanding fire retardance, and this strategy provided a feasible pathway towards the high-value application of fast-growing wood. Full article

Furfurylation is an effective and green method for wood or bamboo modification that can significantly improve its physical and mechanical properties and the resistance against biological deterioration and the attack of subterranean termites. To elucidate the effect of furfurylation on the physical and multiscale mechanical properties of bamboo, the conditions of the furfurylation process were modified to cause an independent variation of the physical and multiscale mechanical properties in differently-treated bamboo samples. This was achieved by impregnating bamboo samples with solutions containing 15%, 30%, 50%, or 70% furfuryl alcohol (FA) by either of the two impregnation processes, vacuum pressure (V-P) and soaking (S) impregnation, while applying different curing conditions (wet- or dry-curing). The physical properties we measured included the absorption rate, weight percent gain (WPG), swelling efficiency (SE), and anti-swelling efficiency (ASE); the macro-mechanical properties involved the modulus of rupture (MOR), the modulus of elasticity (MOE), parallel-to-grain compressive strength (CS), and tensile strength (TS); the micro-mechanical properties included the tensile strength of bamboo’s vascular bundle and hardness and the indentation modulus of bamboo’s fiber cell walls. Finally, the correlation between the different physical and mechanical properties of the modified bamboo samples was analyzed. The results indicate that V-P impregnation made bamboo more permissible for the penetration of FA, while wet-curing was more conducive to ensuring a high curing rate. The dimensional stability of the bamboo samples treated with a high FA concentration through V-P impregnation and of those furfurylated by the S-Wet process using either medium or high FA concentrations was significantly increased. However, the dimensional stability of the bamboo samples modified with either low or medium FA concentrations decreased in both dry and wet curing. In terms of mechanical strength, furfurylation had little effect on the macro- and micro-mechanical properties of bamboo and was slightly improved in comparison to untreated samples. The results also showed a positive correlation between the macro- and micro-mechanical strength of the modified bamboo samples and a significant negative correlation between the mechanical strength and ASE. In soaking impregnation, the WPG and ASE were positively correlated, while the WPG and CS were negatively correlated. Interestingly, the correlation between the mechanical properties and ASE was not significant. Finally, both V-P-Wet and S-Wet approaches can be recommended for bamboo furfurylation, the former being time-saving and having a high curing rate in FA resin while significantly improving the moisture absorption and mechanical strength of bamboo. The advantage of the latter process is simplicity, a high utilization rate of FA, and a significant improvement in the dimensional stability of bamboo. Full article

In this study, fire-retardant plywood was fabricated using a simple guanidine phosphate (GP) impregnation treatment of the veneers, and the influence of the treatment on the flame resistance and bonding strength of the plywood was fully investigated. The results showed that GP modification could effectively endow the plywood with excellent fire resistance and smoke-suppression effect. When 10% GP solution was applied, the limiting oxygen index (LOI) of the impregnated wood was up to 37%, which was almost twice of unmodified plywood. The heat-release rate (HRR) and total smoke production (TSP) were also greatly decreased from the pristine 94.14 MJ/m² and 0.77 m² to that of modified 43.94 MJ/m² and 0.08 m², respectively. The excellent fireproof performance was mainly due to the thermal decomposition of GP to phosphoric acid and guanidine during combustion, which could promote the catalytic carbonization of wood and release of incombustible CO₂ and NH₃ to dilute and decrease the combustible gases, thus collectively preventing the wood form burning. However, the guanidine phosphate modification could seriously damage the bond performance of plywood, especially the UF resin adhesive-bonded plywood. When 10% guanidine phosphate was applied, the dry and wet bonding strength of the UF resin adhesive-bonded plywood were decreased to only 0.7 MPa and 0.12 MPa, respectively, which may be due to the blocking effect of GP in wood pores and the hygroscopic and soluble properties of GP itself in water, thus decreasing the effective bonding between wood veneers. What’s worse, the poor water resistance of the UF resin adhesive was also adverse to the bonding strength of plywood. Surprisingly, the PF resin adhesive was proved to be suitable for gluing the GP-modified wood without obviously decreasing the bonding strength, which could be used to prepare plywood with both high bonding strength and flame resistance. Full article

Waterlogged archaeological wood samples may degrade during long-term immersion in microbial-activity environments, which causes its biodegradation. Simultaneous dynamic vapor sorption (SDVS) and two-dimensional correlation infrared (2D COS-IR) spectroscopy reveal the degradation inhomogeneity of waterlogged fir wood from the Shengbeiyu shipwreck. The waterlogged and reference wood exhibit type II sorption isotherms. The equilibrium moisture contents of waterlogged archaeological fir wood from a decay region (WFD) were 22.5% higher than those of waterlogged archaeological fir wood from a sound region (WFS). WFD exhibits a higher measurable sorption hysteresis than WFS, implying greater variation in the surface moisture content in the WFD region compared to the WFS region, which may compromise the dimensional stability of the shipwreck. 2D COS-IR spectra confirmed the inhomogeneous degradation of the waterlogged wood via numerous mechanisms. The efficacy of SDVS and 2D COS-IR spectroscopy in the evaluation of the degradation state of waterlogged wood was demonstrated. This study verifies the existence of hygroscopic and chemical differences between visually similar samples from the same shipwreck. Full article