The present study evaluates the mold fungal resistance of newly developed loose-fill thermal insulation materials made of wheat straw, corn stalk and water reed. Three distinct techniques for the processing of raw materials were used: mechanical crushing (Raw, ≤20 mm), thermo-mechanical pulping (TMP) with 4% NaOH and steam explosion pulping (SEP). An admixture of boric acid (8%) and tetraborate (7%) was applied to all processed substrates due to their anti-fungal properties. The fourth sample group was prepared from SEP substrates without added fungicide (SEP*) as control. Samples from all treatments were separately inoculated by five different fungal species and incubated in darkness for 28 days at 28 °C and RH > 90%. The highest resistance to the colonization of mold fungi was achieved by TMP and SEP processing, coupled with the addition of boric acid and tetraborate, where molds infested only around 35% to 40% of the inoculated sample area. The lowest mold fungi resistance was detected for the Raw and SEP* samples, each ~75%; they were affected by rich amount of accessible nutrients, suggesting that boric acid and tetraborate additives alone did not prevent mold fungal growth as effectively as in combination with TMP and SEP treatments. Together, the achieved fungal colonization scores after combined fungicide and pulping treatments are very promising for the application of tested renewable materials in the future development of thermal insulation products. Full article

Traditional wood–polymer composite (WPC) based on the in situ polymerization of ethylene unsaturated monomers in the cellular cavity of wood is significant for the high-value-added utilization of low-quality wood. However, this type of WPC has the problems of volatile monomers, low conversion rates, odor residue, and poor compatibility between the polymer and wood interface, which hinder its promotion and application. In this study, a two-step process of cell wall bulking in combination with cell lumen filling was prepared to modify wood using Maleic anhydride (MAN) as the bulking agent and GMA-EGDMA (molar ratio 2:1) as the active monomer system. The results indicate that the modulus of rupture (MOR) (125.19 ± 8.41 MPa), compressive strength (116.38 ± 7.69 MPa), impact toughness (55.4 ± 2.95 KJ m⁻²), and hardness (6187 ± 273 N) of the bulking–filling wood composite materials were improved by 54%, 56%, 36%, and 66%, respectively, compared with those of poplar wood. These properties were superior to those of the traditional styrene (PSt)-WPC and even exceeded the performance of Xylosma congesta (Lour.) Merr, a high-quality wood from northeast China. Meanwhile, the mass loss of wood composite materials with bulking–filling treatment was only 2.35 ± 0.05%, and the internal structure remained intact, presenting excellent decay resistance. Additionally, the treatment also significantly improved the thermal and dimensional stability of the wood composites. This study provides a theoretical basis and guidance for realizing the high-value-added application of low-quality wood and the preparation of highly durable wood-based composites. Full article

Among the material extrusion technologies of additive manufacturing, fused granular fabrication is playing a bigger role in the industry. The increase in the size of printers demands extrusion systems with higher deposition rates that facilitate printing larger parts in shorter times with a need for cost reduction. This cost reduction in fused granular fabrication systems is due to the utilisation of pellets as the material source for the prints, such as pellets that are the most common way of distributing polymeric materials in industry and do not need the usual previous transformation into filaments. Most of the polymers in the industry can be found in the shape of pellets, so the opportunities for developing new materials beside the traditional filaments found in the market are expanding. In this research, a novel composite material has been developed based on the blending of commercial thermoplastic polyurethane (TPU) and cork particles obtained from industrial waste at different concentrations. These materials have been processed at a laboratory scale, and their mechanical, thermal and rheological properties have been studied. Despite a 53.52% reduction in the maximum stress on the x-axis, an 81.82% decrease in the values obtained with specimens oriented on the z-axis and a shortage in the deformation values, the results reveal a remarkable weight reduction leading to 21.31% when compared to the TPU of the blends,. These results may open a path to further explore these blends and find suitable applications in industry as proposed. Full article

In this study, specimens were prepared from Japanese cedar (Cryptomeria japonica) with different thicknesses to determine the best hot-pressing conditions for wood compression layered structural materials (WCLS) through densification at various temperatures and compressing time conditions. However, residual stress-releasing after densification recovery can cause dimensional instability. To address this issue, the drying set method was combined with the compression-set recovery test to determine the best setting time. As a result, the bending strength and modulus of rupture (MOR) of WCLS increased by 9.98 ± 9.71 to 20.87 ± 13.09% and the modulus of elasticity (MOE) increased by 9.87 ± 11.92 to 22.40 ± 17.97%. The volumetric swelling coefficient (S), water absorption percent (WAP), and equivalent moisture content (EMC) decreased as the drying time increased. The anti-swelling efficiency (ASE) and moisture excluding efficiency (MEE) were found to be the highest at a drying time of 12 h, with values ranging from 13.20 ± 15.11 to 36.46 ± 6.83% and 15.18 ± 1.11 to 19.58 ± 8.31%, respectively. The drying method was found to be effective in increasing dimensional stability. The glass transition temperature (Tg) moved to a lower temperature as the compression-set increased, which was due to plasticization of wood caused by high temperature and pressure. The cell walls of WCLS presented viscous buckling, which provided effective dimensional stability. The thermal conductivity of Japanese cedar and each compression-set WCLS were 0.1863 ± 0.0071, 0.1520 ± 0.0147, 0.1817 ± 0.0106, and 0.1423 ± 0.0137 W/mK, respectively. The thermal conductivity of each WCLS increased with an increase in compression-set, but decreased by 10.67 to 22.52% compared to Japanese cedar. The total electricity energy consumption of each WCLS after 24 h of testing decreased with a trend of 30.50 ± 0.84, 29.83 ± 0.42, 29.57 ± 0.51, and 29.4 ± 0.36 kWH. Full article

Since the chemical composition of wood is closely related to its mechanical properties, chemical analysis techniques such as near-infrared (NIR) spectroscopy provide a reasonable non-destructive method for predicting wood strength. In this study, we used NIR spectra with principal component analysis (PCA) to reveal that vacuum hydrothermal (VH) treatment causes degradation of hemicellulose as well as the amorphous region of cellulose, resulting in lower hydroxyl and acetyl group content. These processes increase the crystallinity of the luanta fir wood (Cunninghamia konishii Hayata), which, in turn, effectively increases its compressive strength (σ_c,max), hardness, and modulus of elasticity (MOE). The PCA results also revealed that the primary factors affecting these properties are the hemicellulose content, hydroxyl groups in the cellulose amorphous region, the wood moisture content, and the relative lignin content. Moreover, the ratios of performance deviation (RPDs) for the σ_c,max, shear strength (σ_s,max), hardness, and modulus of rupture (MOR) models were 1.49, 1.24, 1.13, and 2.39, indicating that these models can be used for wood grading (1.0 < RPD < 2.5). Accordingly, NIR can serve as a useful tool for predicting the mechanical properties of VH-treated wood. Full article

This study used the luanta fir (Cunninghamia konishii Hayata) wood, one of the most used wood construction and building materials in Taiwan, as specimens to examine the impact of different conditions of vacuum hydrothermal (VH) treatment on the physical properties of this wood. A prediction model for these properties was created using a nondestructive spectroscopy technique. The test results revealed that the mass loss, moisture exclusion efficiency, anti-swelling efficiency, color difference, and surface contact angle of the VH-treated wood all increased under increasing heat treatment temperature and time. Moreover, the use of near-infrared (NIR) spectroscopy in creating the prediction model for the physical properties of the VH-treated luanta fir wood revealed that the ratios of performance to deviation (RPD) for mass loss, equilibrium moisture content, and color difference were all above 2.5, indicating a high prediction accuracy. These results suggested that an NIR spectrometer can serve as a useful instrument for the accurate prediction of the physical properties or for controlling the quality of VH-treated wood. Full article

Incorporation of short wood fillers such as wood flour (WF) into polypropylene (PP) often results in a marked reduction of toughness, which is one of the main shortcomings for WF/PP composites. This research reports a facile approach to achieve toughening of WF/PP composites via introducing self-assembling β-nucleating agents into PP matrix. The effect of two kinds of nucleating agents, an aryl amide derivative (TMB5) and a rare earth complex (WBG II), at varying concentrations on the crystallization and mechanical properties of WF/PP composites was comparatively investigated. The results showed that both nucleating agents were highly effective in inducing β-crystal for WF/PP, with β-crystal content (k_β) value reaching 0.8 at 0.05 wt% nucleating agent concentration. The incorporation of TMB or WBG significantly decreased the spherulite size, increased the crystallization temperature and accelerated the crystallization process of WF/PP. As a result of PP crystalline modification, the toughness of composites was significantly improved. Through introducing 0.3 wt% TMB or WBG, the notched impact strength and strain at break of WF/PP increased by approximately 28% and 40%, respectively. Comparatively, although WF/PP-WBG had slightly higher K_β value than WF/PP-TMB at the same concentration, WF/PP/TMB exhibited more uniform crystalline morphology with smaller spherulites. Furthermore, the tensile strength and modulus of WF/PP-TMB were higher than WF/PP-WBG. This matrix crystalline modification strategy provides a promising route to prepare wood filler/thermoplastic composites with improved toughness and accelerated crystallization. Full article

Wood delignification can provide a wood-based template with sufficient pore volume for polymer/wood composites. At the same time, delignification is conducive to the penetration of polymer into the wood cell wall, which is of great significance to improve the function and performance of composites. However, lignin is the main chemical component in wood. The removal of lignin will inevitably lead to the change of the wood’s physical properties, including the hygroscopicity of the wood. In this study, prepolymerized methyl methacrylate (MMA) impregnated delignified wood (DW) was used to obtain polymerized methyl methacrylate/delignified wood (PMMA/DW) composites with different lignin removal. The effect of lignin removal on the hygroscopicity of the composites is discussed. The results of nitrogen adsorption showed that the DW could adsorb more nitrogen than the original wood, and the amount of nitrogen adsorption gradually increased with the improvement of the processing degree. After filling with PMMA, the adsorption amount of nitrogen was greatly reduced. The results of the BET analysis showed that delignification promoted the distribution of PMMA in the pores of the wood cell wall. When lignin was almost completely removed, all mesopores in the cell wall were filled with PMMA. The results of the moisture absorption analysis isotherm curve showed that the moisture absorption content of the wood was positively correlated with the amount of lignin removed, and the moisture absorption content of the PMMA/DW composite was negatively correlated with the amount of lignin removed. The hygroscopic data were further analyzed using the Hailwood–Horrobin model. The results showed that the mole number of adsorbable or hydratable sites of the DW increased with the increase of lignin removal, and the situation of the PMMA/DW composites was just the opposite. In addition, after delignification, the dissolved water content and hydrated water content of the DW increased, and the increase was related to the delignification strength. The increase of dissolved water content indicates that the removal of lignin promotes the production of more volume in the cell wall, which provides space for the adsorption of multilayer water. After MMA in situ polymerization, the hydration and dissolved water content of the PMMA/DW decreased significantly, and the dissolved water content decreased even more significantly. The fitting curves of the H-H model and GDW model for the experimental data points of the differently treated samples were similar. The removal of lignin led to the increase of the w value, indicating that the ratio of water molecules adsorbed in the first layer of DW to the second layer increased, and the removal of lignin resulted in the enhancement of wood hygroscopicity; the opposite was true for the PMMA/DW. Full article

Various mechanisms of plant organ movements have been reported, including the close association of two layers with expressed differences in hygroscopic properties. Following this principle, actuator beams composed of thin veneers out of normal and compression wood cut from Scots pine (Pinus sylvestris L.) were prepared by using two types of adhesives. The mismatch of the swelling properties of the two layers in tight combination resulted in an expressed bending deflection in response to set humidity changes. The resulting curvatures were measured and analyzed by the Timoshenko bi-metal-model, as well as with an enhanced three-layer model, with the latter also considering the mechanical influence of the glueline on the actuator bending. The thermally induced strain in the original model was replaced by another strain due to moisture changes. The strain was modelled as a function of wood density, along with changes in wood moisture. Experiments with free movement of the bilayer to measure curvature, and with constraints to determine forces, were performed as well. Deformation and magnitude of actuators movements were in close agreement with the enhanced bilayer-model for the phenol-resorcinol-formaldehyde adhesive, which deviated substantially from the casein adhesive glued actuators. The obtained results are seen as critical for wood-based actuator systems that are potentially used in buildings or other applications. Full article

Fast-growing poplar wood has the bottleneck problems of inferior mechanical strength and poor dimensional stability. In this study, the wood was modified by combined treatments of pre-compression and post-vacuum-thermo modification to improve its mechanical strength and dimensional stability, simultaneously; in addition, the variation law of mechanical properties of the wood with compression ratio as well as the improvement effect of dimensional stability of the treated wood were mainly studied. The results show that the optimal temperature and time of the vacuum-thermo modification were 190 °C and 10 h, respectively. Under these conditions, the structure of pre-compressed and post-vacuum-thermally modified wood (CT wood) is gradually densified with the increase in the compression ratio, which results in the continuous enhancement of mechanical properties. Meanwhile, the anti-swelling efficiency (ASE) of the CT wood after water absorption is correspondingly better than that of the compressed wood before thermal modification, indicating that the dimensional stability of compressed wood was improved by the thermal modification. When the compression ratio was 70%, the modulus of rupture (MOR) and impact toughness of CT wood was 176 MPa and 63 KJ/m², which was 125% and 59% higher than that of untreated wood, respectively. The ASE was also 26% higher than that of the wood with sole compression. Therefore, this method improves the mechanical strength and dimensional stability of wood simultaneously, and it provides a scientific basis for optimization of the reinforcing modification process of fast-growing wood. Full article