In this article, the low-field nuclear magnetic resonance was used to measure the moisture content (MC) and MC profiles in poplar wood during real-time drying. The T₂ distribution curve at each drying stage measured using the Carr–Purcell–Meiboom–Gill pulse sequence provided detailed information in the dynamic change of free water as well as bound water of the whole wood sample. In addition, a new developed SE-SPI pulse sequence was first used to evaluate the spatially resolved T₂ distribution of the successive nondestructive sliced layer of wood. Combined with the area integration method, the moisture content in each layer was calculated, and the change of MC profiles within wood at the MC above and below fiber saturation point was well reflected.

The hydrophilicity and flammability of fiberboards have limited their real-life applications. In this study, a facile strategy for preparing the multifunctional coatings with superhydrophobicity and flame retardancy on medium density fiberboards (MDFs) has been investigated. The superhydrophobic and flame-retardant coating on the MDF surface was obtained by depositing polydimethylsiloxane (PDMS) and 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane (FDTS)-modified Mg/Al layered double hydroxide (LDH) particles step by step. The as-prepared coating exhibited superhydrophobic properties with a water contact angle (WCA) of ~155° and good self-cleaning properties. Furthermore, the limiting oxygen index (LOI) value of the superhydrophobic MDFs increased by 60.4% as compared to that of the pristine MDFs, showing improved flame retardancy. The peak heat release rate (PHRR) and total heat release (THR) of MDFs decreased after coating with PDMS@FDTS-Mg/Al LDH, suggesting that the superhydrophobic coating decreased the fire growth speed and risk of fire hazard of MDFs. This coating with multiple functions opens a new avenue for the protection and functionalization of MDFs.

Knowledge of the dynamic changes in the water absorption process of heat-treated wood is important for providing a scientific basis for the reasonable application of heat-treated wood, especially for outdoor applications. Nuclear magnetic resonance (NMR) techniques provide detailed information about the moisture components and moisture transport processes in wood, which are not available with other methods. In this work, water absorption of untreated and heat treated Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) heartwood was investigated using various NMR methods. The heat treatment temperatures were varied between 160 °C and 220 °C. According to the spin-spin relaxation time (T₂), there were two components of water in the samples heat-treated at 160 °C and 180 °C as well as the untreated sample, while three components of water were found in the samples heat-treated at 200 °C and 220 °C, and the mass of each component was calculated by the integral peak areas of the T₂ curve. The amount of bound water and free water in heat-treated samples were less compared to the untreated ones, and the water absorption decreased correspondingly, due to the increasing heat-treated temperature. The results obtained by one dimensional frequency coding indicated that the heat treatment made wood difficult to be accessed by moisture. Besides, NMR images revealed that the free water absorption in latewood was faster than in earlywood, but earlywood could absorb more water than latewood.

To examine the methodology for determining the moisture diffusion behavior of lignocellulosic biomass in steady and unsteady states (two stages of a sorption isotherm), the diffusion coefficients in the steady and unsteady states (D _SS and D _US) were investigated over a range of relative humidity (RH) from 10 to 90% using a dynamic vapor sorption (DVS) apparatus and a specifically designed cell kit. Thin samples with a thickness of 50 μm were prepared from three lignocellulosic biomasses, i.e. poplar, Chinese fir and moso bamboo. Based on Fick’s first and second laws, D _SS and D _US were determined. An increase in D _SS or D _US was observed with increasing equilibrium moisture content (EMC) or transient status, regardless of the lignocellulosic biomass species. The moisture-dependent D _SS of poplar, Chinese fir and moso bamboo was similar to values previously reported. Chinese fir and moso bamboo exhibited the highest and the lowest D _SS values, respectively, when the same EMCs were achieved. The results of this study revealed that D _SS and D _US of lignocellulosic biomass (even with limited dimensions) could be determined during a sorption isotherm in a wide humidity range. Furthermore, the results are helpful for simulating moisture transport behaviors in the fields of drying, paper packaging and wooden building maintenance.

To clarify the effects of drying temperature on the hygroscopicity and mechanical performance of MUF resin-impregnated wood, we investigated the water vapor adsorption capability, modulus of rupture (MOR), modulus of elasticity (MOE), and surface hardness of MUF resin-impregnated wood treated at 60, 80, 100, 120, 140 °C. Drying temperature can influence the hygroscopicity of MUF resin-impregnated wood. As temperature increased, hygroscopicity typically decreased, but the resin-impregnated wood hygroscopicity increased after treatment at 60 °C. Drying temperature has shown significant influence on the mechanical performance of MUF resin-impregnated wood (α = 0.01). Increasing the treatment temperature can enhance the mechanical performance of resin-impregnated wood. However, brittleness of the resin-impregnated wood increased after treatment at 140 °C. Characterization of FTIR and ¹³C CP/MAS NMR indicate that higher drying temperature led to lower content of hydroxymethyl groups and more substituted reactive sites on the amino group. This refers to more complete dehydration condensation between the resin active groups, thereby increasing the crosslinking density of the resin, increasing the cohesive strength, and decreasing the hygroscopic groups.