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Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) is a widely planted species of plantation forest in China, and heat treatment can improve its dimensional stability defects and improve its performance. The wood samples were heat-treated at various temperatures (160, 180, 200, and 220 °C) for 2 h. To clarify the effect of heat treatment on wood hygroscopicity, the equilibrium moisture content (EMC) was measured, the moisture adsorption and desorption rates were determined, the hygroscopic hysteresis was examined, and the Guggenheim, Anderson, and de Boer (GAB) model was fitted to the experimental data. The moisture absorption isotherms of all samples belonged to the Type II adsorption isotherm, but the shape of the desorption isotherm was more linear for heat-treated wood samples, especially when the heat treatment temperature was higher. According to the results analyzed with ANOVA, there were significant differences in equilibrium moisture content between the control samples and the heat-treated samples under the conditions of 30%, 60%, and 95% relative humidity (RH, p < 0.05), and the results of multiple comparisons were similar. The decrease in hygroscopicity was more pronounced in wood treated at higher temperatures. The EMC of the 160–220 °C heat-treated samples of the control samples was 14.00%, 22.37%, 28.95%, and 39.63% lower than that of the control sample at 95% RH. Under low RH conditions (30%), water is taken up mainly via monolayer sorption, and multilayer sorption gradually predominates over monolayer sorption with the increase in RH. The dynamic vapor sorption (DVS) analysis indicated that the heat-treated wood revealed an increase in isotherm hysteresis, which was due to the change in cell wall chemical components and microstructure caused by heat treatment. In addition, the effective specific surface area of wood samples decreased significantly after heat treatment, and the change trend was similar to that of equilibrium moisture content. [ABSTRACT FROM AUTHOR]

Wood wettability, the process of liquid interaction with wood surfaces, is influenced by wood surface chemistry, structure, ambient conditions, and temperature. Understanding how temperature impacts wood wettability is crucial for high-temperature manufacturing processes. In this study, the sessile drop method was employed to explore the dynamic wettability of Chinese fir wood using three different liquids (water, glycerol and polyvinyl acetate (PVAc)) across a range of temperatures (25, 40, 60 and 80 °C). By considering spreading, penetration and evaporation, we revealed that the dynamic wettability of Chinese fir was strongly dependent on temperature and the type of liquid. Temperature elevation enhances wettability, leading to reduced contact angles and increased penetration ratios. Water exhibited the highest wettability, followed by glycerol, with PVAc being the least wetting agent. Notably, after 180 s of wetting at 80 °C, the measured contact angles were 0° for water, 45° for glycerol, and 120° for PVAc. When accounting for evaporation, the penetration of water decreased from 57 % to 47 % (25 °C) and 100 % to 62 % (80 °C). The activation energies for the penetration of water and PVAc into Chinese fir exhibited variations, with values of 35.3 and 158.3 kJ/mol, respectively. These comprehensive wetting results, covering spreading, penetration and evaporation, provide valuable insights into wood–water and wood–adhesive interactions, particularly when exposed to high-temperature conditions. [ABSTRACT FROM AUTHOR]

Transparent wood (TW) is an emerging composite material made of wood and infiltrated polymer that holds great promise for use in outdoor building components and photovoltaic devices. To assess the weathering resistance of TW, we conducted artificial weathering tests on three types of TW infiltrated with different polymers: epoxy (ETW), methyl methacrylate (MTW), and polyvinylpyrrolidone (PTW). After 360 h of artificial weathering, ETW and PTW exhibited less surface roughness, color difference, and volumetric swelling compared to MTW. The equilibrium contact angle rankings were: ETW (42°) > MTW (31°) > PTW (28°). The transmittances of PTW and MTW remained above 60% after weathering, and that of ETW dropped to 40%. Chemical analysis indicated that PTW was least affected by UV-induced degradation, followed by ETW, while MTW was the most severely impacted. Our comprehensive assessment revealed that the weathering resistance of TW can vary depending on the polymer type, with ETW and PTW demonstrating superior resistance compared to MTW. These findings highlight the potential of TW as a durable and sustainable material for outdoor applications and provide valuable data for optimizing the development and utilization of TW. [ABSTRACT FROM AUTHOR]

Ultraviolet light-induced discoloration is a noticeable issue when heat-treated wood is used outdoors. In this study, titanium dioxide (TiO2) particles were electrochemically deposited on the surface of heat-treated wood via a high-voltage electrostatic field (HVEF). Natural and artificial weathering tests were carried out to evaluate the anti-weathering properties after the electrochemical deposition. During HVEF treatment, Ti particles were triggered in the form of Ti4+. Ti4+ grafted with the hydroxyl groups of hemicellulose and lignin in the form of Ti–OH, and TiO2 was produced due to the oxidizing atmosphere generated by HVEF. TiO2 and Ti–OH played roles as UV absorbers, reducing degradation and discoloration of heat-treated wood. The photodegradation of lignin was alleviated effectively during both the artificial and natural weathering. The stability of wood color was remained. After the artificial weathering, the values of L*, a* and b* of the electrochemical depositied sample were 55, 10 and 25, respectively. The leaching amount of TiO2 after artificial or natural weathering was less than 6% or 40%, respectively determined by atomic absorption spectroscopy. The results suggest the feasibility of the electrochemical deposition of TiO2 for improving the anti-weathering properties of heat-treated wood and provide an effective strategy for industrial wood modification. [ABSTRACT FROM AUTHOR]

The moisture content of wood is changed during manufacturing processes, such as drying and impregnation. Understanding the water transport in wood is helpful for optimizing the manufacturing technology and improving the durability of wood products. Herein, the one-side imbibition tests of Chinese fir and poplar were carried out via direct contact with a water-saturated sponge. Imbibition amounts and orthotropic kinetics were evaluated by X-ray densitometry, where wood exhibited non-uniform and directional behaviors for water imbibition and there were variations in behavior between Chinese fir and poplar. More water uptake and faster migration were observed for poplar, while water preferentially accumulated at the wetting front for Chinese fir. The effective imbibition height of poplar was significantly higher than Chinese fir, regardless of orientation direction. Within the growth rings, Chinese fir showed heterogeneous water uptake, and faster water migration in latewood was observed. Imbibition height in a single fiber was simulated as a function of cell wall ratio, and the influences of anatomical factors on water movement were explored. These simulation assessments were consistent with the results of the one-side imbibition tests. These findings help to explain the water transport mechanism at the mesoscale and interactions between wood and water. [ABSTRACT FROM AUTHOR]

Temperature and time dependence of orthotropic viscoelastic properties for Chinese fir wood (Cunninghamia lanceolata) were investigated in tensile mode. The storage modulus (E′) and loss modulus (E″) of the longitudinal (L), radial (R) and tangential (T) specimens with adsorbed water were determined during temperature increasing period ranging from 30°C to 103°C and at a constant temperature of 103°C for 480 min. The desorption of adsorbed water provided space for the rearrangement of hydrogen bonds (RHB) within the polymer networks and caused mechano-sorptive (MS) effect. During the temperature increasing period, the MS effect increased first and following decreased for all specimens, except for the T specimens with 7.2% moisture content. In a constant temperature process, elevated stiffness and decreased damping were observed in all orthotropic directions, which suggested that the RHB effect was prominent than the dual effects of the MS and heating. Compared to the L specimens, the multi-effects of the heating, RHB and MS exerted more influence on the R and T specimens. Meanwhile, the unstable state within wood cell walls in the R and T specimens was more pronounced than that in the L specimens. Furthermore, the transverse specimens were affected by temperature to a higher degree than that of the L specimens. [ABSTRACT FROM AUTHOR]

Differences in the orthotropic viscoelastic properties of Chinese fir wood (Cunninghamia lanceolata) during cooling and heating variations were investigated in the temperature range between −120°C and 25°C. The stiffness and damping of the longitudinal (L), radial (R), and tangential (T) specimens were determined for five equilibrium moisture content (EMC) levels ranging from 0.6% to 25.2%. Results showed that the tensile storage modulus (E′) values in the cooling run were lower than those in the heating run at each temperature, regardless of the grain orientation and EMC level. The absolute value of the changing rate of E′ (|ΔE′|) in the cooling run was more pronounced than that in the heating run. The values of |ΔE′| demonstrated an anisotropy at all EMC levels, while the |ΔE′| of L specimens were lower than that of transverse specimens. Compared to per unit temperature, per unit moisture content exerted more influence on the stiffness of specimens. The γ-relaxation was observed in the loss modulus (E′′) and loss factor (tanδ) temperature spectrum. The γ-relaxation peak temperature in the E″ temperature spectrum was lower than that in the tanδ spectrum. The γ-relaxation peak temperature in the cooling run was lower than that in the heating run, irrespective of the grain orientation. Furthermore, the γ-relaxation peak temperature shifted to a lower temperature range with an increasing amount of adsorbed water, independent of cooling and heating runs. [ABSTRACT FROM AUTHOR]

Unraveling the impact of lignin reduction on cell wall construction of poplar stems is important for accurate understanding the regulatory role of biosynthetic genes. However, few cell-level studies have been conducted on the changes in lignin, other important cell wall composition, and the structural properties of transgenic poplar stems at different developmental stages. In this work, the content and microdistributions of cell wall composition as well as the morphological characteristics of cells were studied for p -hydroxycinnamoyl-coenzyme A:quinate/shikimate p -hydroxycinnamoyltransferase (HCT) downregulated transgenic poplar 84K (Populus alba × P. glandulosa cl. '84k') at different developmental stages. Results show that the lignin contents of the upper, middle, and basal parts of HCT transgenic poplar stems were significantly decreased by 10.84, 7.40, and 7.75%, respectively; and the cellulose contents increased by 8.20, 6.45, and 3.31%, respectively, compared with the control group. The cellulose/lignin ratio of HCT transgenic poplars was therefore increased, especially in the upper sections, where it was 23.2% higher. Raman results indicate the appearance of p -hydroxyphenyl units (H) and a decrease in the ratio of syringyl/guaiacyl (S/G) lignin monomers in fiber cell walls of HCT transgenic poplars. In addition, microstructure observations revealed that the fiber and vessel cells of the HCT transgenic poplars exhibited thin cell walls and large lumen diameters. Compared with the control group, the cell wall thickness of fiber and vessel cells decreased by 6.50 and 10.93% on average, respectively. There was a 13.6% decrease in the average ratio of the cell wall thickness to the lumen diameter and an increase in fiber length and width of 5.60 and 6.11%, respectively. In addition, downregulation of HCT did not change the orientation of cellulosic microfibrils, but it led to an 11.1% increase of the cellulose crystallinity in cell walls compared to the control poplars. The information obtained herein could lead to a better understanding of the effects of genetic modifications on wood cell walls. [ABSTRACT FROM AUTHOR]

Mechanical testing, microscopic image analysis, and X-ray diffraction were used to study the mechanical properties and their correlation with microstructure in three 20-year-old Chinese fir clones (Kailin 24, Kaihua 13, and Kaihua 3). The Chinese fir clones featured a modulus of rupture (MOR) of 52–59 MPa, a modulus of elasticity (MOE) of 10–11 GPa, and a compressive strength parallel to the grain of 31–34 MPa. Kaihua 13 and Kailin 24 had similar mechanical properties and were superior to Kaihua 3 among the tree clones. Radial variation indicated that their outerwood (rings 9–18) had better mechanical properties than their corewood (rings 3–7). Kaihua 13 with better mechanical properties had a larger ratio of cell wall to lumen than Kaihua 3 and Kailin 24. Outerwood with better mechanical properties also had a larger ratio of cell wall to lumen and a smaller microfibril angle compared to corewood with poor mechanical properties. Linear regression analysis also shows that for various clones and different radial positions in the same clone, anatomical structure parameters such as average cell wall thickness and the ratio of cell wall to lumen were positively correlated to their mechanical properties, while the microfibril angle was negatively correlated to mechanical properties. The two factors synergistically influence the mechanical properties of wood. [ABSTRACT FROM AUTHOR]

With the increasing shortage of timber resources and the advancement of environmental protection projects, many artificial fast-growing forests are planted and used as raw materials in China. There are significant differences in the properties of natural forest wood and artificial fast-growing forest wood, and the properties of wood mainly depend on the change in the status of bound water in the cell wall. In this study, the fiber saturation point (FSP) and pore size distributions within the cell wall of six species of fast-growing forest wood were studied by low-temperature nuclear magnetic resonance (NMR) technology. The effects of species, growth rings, and extractives on the FSP and pore structure were analyzed. The water vapor sorption experiments were performed, and the adsorption isotherms of the samples were fitted through the Guggenheim-Anderson-de Boer (GAB) equation. According to the least-square regression of the adsorption isotherms and combined with the low-temperature NMR experiments, the content and proportion of the different types of bound water were analyzed. The results showed that the average FSP of each Chinese fir was about 40% and that of each poplar was about 35%. There is about a 10% difference between the FSP measured by NMR technology and the adsorption bound water content obtained by adsorption isothermal. The pore size distribution results show that in all samples, the proportion of pores larger than 10.5 nm is very low, about 10%; the proportion of 1.92-10.5 nm pores is about 30%; and the proportion of pores smaller than 1.92nm is more than 50%. This work will be helpful to the study of the wood moisture status and provide reference data for wood modification. [ABSTRACT FROM AUTHOR]

The dimensional instability and inferior mechanical strength of radiata pine (Pinus radiata D. Don) limit its use in musical instruments. To improve its properties, a two-step treatment by furfuryl alcohol (FA) and tung oil (TO) were used involving impregnation of FA precursor solution into the wood matrix, forming a highly cross-linked resin, followed by a modification with TO. Examination using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy revealed that FA resin was attached in cell walls and lumens, and the solidified TO in cell lumens and occluded pits. The incorporation of FA resin reduced the wood swelling coefficient by over 70% and the hydrophobic solidified TO decreased wood water uptake by over 80% enhancing wood dimensional stability. Although FA resin improved the modulus of elasticity and hardness of the wood, the modulus of rupture and impact bending strength were reduced. However, the additional TO impregnation step improved the modulus of rupture, impact bending strength, and wear resistance of the furfurylated wood. The performance of FA and TO treated radiata pine wood was better than that treated with FA or TO alone, and could meet the performance requirements of wood used for fretboard of string instruments. [ABSTRACT FROM AUTHOR]

Compression combined with steam (CS) treatment is postulated to be an environmentally friendly and efficient modification method to improve the dimensional stability, durability, and mechanical strength of wood. The influences of CS treatment with different radial compression ratios (RCRs) (25% and 50%) and different steam temperatures (140, 160 and 180°C) on chemical components, porosity, and hygroscopicity of earlywood and latewood in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) were investigated respectively on a cellular level by imaging Fourier Transform Infrared (FT-IR) microscopy, Confocal Raman Microscopy (CRM), nitrogen adsorption and dynamic vapor sorption (DVS). The results indicated that the degradation of carbonyl groups of the glucuronic acid component of xylan in earlywood and latewood was mainly responsible for the low hygroscopicity of CS-treated wood. Also, a significant decrease in the amount of C=O and C=C linked to the lignin aromatic skeleton involved in either crosslinking reactions or the degradation reactions could be another contributor to the reduction in wood hygroscopicity. CS-treated wood with a steam temperature of 180°C possessed a lower hygroscopicity that correlated well with the depolymerization of crystalline and amorphous cellulose. A more deformed structure of CS-treated wood led to the formation of greater amounts of mesopores in the cell walls, which could lead to increased degradation of the chemical components of wood cell walls. Furthermore, a higher equilibrium moisture content (EMC) level was found for CS-treated wood with a 50% compression ratio compared to a 25% compression ratio. [ABSTRACT FROM AUTHOR]