•Possible reaction paths for the preparation of ACFs from liquefied wood were proposed.•Some incompletely liquefied substances decomposed during carbonization.•Reactions between KOH and carbon began ...at 530°C.•The main gaseous products were H2, H2O, CH4, CO, CO2.
In this study, wood-based fibers were used as raw materials to prepare activated carbon fibers (ACFs) by carbonization at 500°C followed KOH activation at 850°C process. The structure of the fibers was characterized by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analyses. Besides, the volatiles of the final products were determined by thermogravimetry-mass spectrometry (TG-MS) and titration. The reaction mechanisms were consequently deduced. In the first carbonization process, it was mainly related to substitution, scission, and oxidization reactions of methylene. And in the second activation process, KOH and carbon began to react at 530°C, resulting in potassium compounds, which further reacted with carbon. Meanwhile, temperature elevation caused polycyclic reactions, which made the ACFs a graphite-like microcrystalite structure.
This review summarizes the development of the experimental technique and analytical method for using TD-NMR to study wood-water interactions in recent years. We briefly introduce the general concept ...of TD-NMR and magnetic resonance imaging (MRI), and demonstrate their applications for characterizing the following aspects of wood-water interactions: water state, fiber saturation state, water distribution at the cellular scale, and water migration in wood. The aim of this review is to provide an overview of the utilizations and future research opportunities of TD-NMR in wood-water relations. It should be noted that this review does not cover the NMR methods that provide chemical resolution of wood macromolecules, such as solid-state NMR.
Chemical modification of wood with green modifiers is highly desirable for sustainable development. With the aim of enhancing the water resistance and dimensional stability of fast growing wood, ...modifications were conducted using renewable and toxicity-free industrial lignin combined with heat treatment. Poplar (
) samples first underwent impregnation with alkali lignin solution and were then subjected to heat treatment at 140⁻180 °C for two hours. The results indicated that the modified wood showed excellent leaching resistance. The alkali lignin treatment improved surface hydrophobicity and compression strength, and decreased moisture and water uptake, thereby reducing the dimensional instability of modified wood. These changes became more pronounced as the heat-treating temperature increased. Scanning electron microscopy, confocal laser scanning microscopy, and Fourier transform infrared spectroscopy evidenced that a multiscale improvement of the alkali lignin occurred in the cell lumen and cell wall of wood fibers and vessels, with small alkali lignin molecules reacting with the wood matrix. This study paves the way for developing an effective modification approach for fast growing wood, as well as promoting the reuse of industrial lignin for high-value applications, and improves the sustainable development of the forestry industry.
To investigate the effect of temperature on the dynamic sorptive and hygroexpansive behavior of wood, poplar (Populus euramericana cv.) specimens, 20 mm in radial (R) and tangential (T) directions ...with two thicknesses of 4 mm and 10 mm along the grain, were exposed to a sinusoidally varying relative humidity between 45 and 75% for 1, 6, and 24 h at 25 and 40 °C. Moisture changes, as well as radial and tangential dimensional changes measured during cycling, produced the following results: moisture and dimensional changes in the specimens were generally sinusoidal, and an increase in temperature led to decreased moisture contents and transverse dimensions, accordingly. The amplitude of moisture and dimensional changes was in positive correlation with temperature, while the phase lag was inversely related to temperature. Sorption hysteresis and swelling hysteresis decreased as temperature increased. Both moisture sorption coefficient (MSC) and humidity expansion coefficient (HEC) were supposed to share the approximate value for different thick specimens if cyclic period is sufficiently long. Transverse anisotropy could be found under dynamic conditions, and the T/R was about 1.65 to 1.75, varying sinusoidally with a phase difference of about a half cycle to the imposed relative humidity.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
To investigate the effects on moisture sorption behavior of wood caused by the removal of chemical components, Populus euramericana flour (40 to 60 mesh) was divided into four groups: untreated, ...extractives removed, hemicellulose removed, and matrix removed. The samples at the fiber saturation point and under oven-dried conditions were separately exposed to relative humidities of 11%, 45%, and 75% at 25 °C for desorption and adsorption. Additionally, moisture changes were measured during the processes. The results showed that moisture changed rapidly for all four groups at the initial stage during sorption, after which the rate gradually decreased until a steady-state equilibrium was reached. Among the four groups, the samples from which extractives had been removed exhibited the highest moisture content and moisture sorption coefficient, followed by the untreated samples, hemicellulose removed, and matrix removed samples. With increasing relative humidity, the hysteresis ratio A/D of the samples increased, indicating a reduction in sorption hysteresis, which was further decreased by hemicellulose extraction.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
In this study, poly(lactic acid) (PLA)/wood flour (WF) composites were prepared by first blending PLA with organo-montmorillonite (OMMT) at different contents (0.5, 1, 1.5, and 2 wt %). The physical ...and mechanical properties of the virgin and OMMT modified PLA and its WF composites were tested. The results showed that: (1) at low OMMT content (<1 wt %), OMMT can uniformly disperse into the PLA matrix with highly exfoliated structures. When the content increased to 1.5 wt %, some aggregations occurred; (2) after a second extruding process, the aggregated OMMT redistributed into PLA and part of OMMT even penetrated into the WF cell wall. However, at the highest OMMT content (2 wt %), aggregates still existed; (3) the highly exfoliated OMMT was beneficial to the physical and mechanical properties of PLA and the WF composites. The optimal group of OMMT-modified PLA was found at an OMMT content of 0.5 wt %, while for the PLA/WF system, the best properties were achieved at an OMMT content of 1.5 wt %.
Effects of chemical components on wood sorption property under dynamic condition were investigated for the first time. Hemicellulose, lignin and extractive (denoted as DHC, DL and DE, respectively) ...were removed from Populus euramericana Cv., 20 mm in radial (R) and tangential (T) directions with thickness of 4 mm along the grain, then the wood was subjected to cyclic tests where relative humidity (RH) varied from 45% to 75% sinusoidally at 25 °C. Based on measured data automatically, the results showed that, various chemical components had different effects on dynamic sorption behaviors of wood. The DL exhibited the largest moisture content and diffusion coefficient, followed by the DE, Control and DHC. This indicated lignin or extractive removal accelerated the dynamic sorption process and improved hygroscopicity of wood, while hemicellulose removal caused opposite effects. Theoretical sorption model was further applied and the modeled curves fitted satisfactorily with experimental data. Dynamic moisture gradient distribution inside the different treated wood was investigated and amplitude of moisture showed negative relation with wood element depth, while phase lag presented an opposite trend. Amplitude of DL was the largest while its phase lag was the least. Conditioning thickness for RH was greatest for DHC, about twice as much as the minimum of DL.
Water dominates the wood cell wall in the hygroscopic range. The state and amount of cell wall water influence the physical and mechanical properties of wood. 2D time-domain nuclear magnetic ...resonance (2D TD-NMR) is capable of resolving cell wall water. To identify the relaxation property of cell wall water, 2D TD-NMR with saturation recovery Carr-Purcell-Meiboom-Gill pulse sequence was applied on
Fagus sylvatica
and
Pinus taeda
L. at equilibrium state under 12, 34, 47, 65, 84, and 97% relative humidity (RH), as well as during adsorption process from dry to 84% RH. The result showed that two pools of cell wall water were identified, the water molecules in disordered surface of cellulose microfibrils and their surrounding hemicellulose (Peak B), and the water molecules in the domain of matrix including lignin and surrounding hemicellulose (Peak C). B-water and C-water exhibited different relaxation properties with different moisture contents. With increasing RH, B-water gained more mobility than C-water. Through the calculation based on cluster theory, it was hypothesized that the formation of water clusters in high RH region may exist in the reservoir of B-water. During the sorption process from a dry state to equilibrium at 84% RH, the amount of B- and C-water gradually increased, whereas B-water appeared earlier than C-water but took a longer time to equilibrate. When the sub-equilibrium state was attained, the T
1/
T
2
ratio stayed stable.
Graphical abstract
To investigate the effects of changes in biopolymer composition on moisture in acetylated poplar wood (Populus euramericana Cv.), the acetylation of control wood was compared to the acetylation of ...wood with reduced hemicellulose or lignin content (about 9% reduction of total specimen dry weight in both cases). Time-domain nuclear magnetic resonance relaxometry of water-saturated wood gave spin–spin relaxation times (T2) of water populations, while deuteration in a sorption balance was used to characterize the hydroxyl accessibility of the wood cell walls. As expected, the acetylation of pyridine-swelled wood reduced hydroxyl accessibility and made the cell wall less accessible to water, resulting in a reduction of cell wall moisture content by about 24% compared with control wood. Hemicellulose loss per se increased the spin–spin relaxation time of cell wall water, while delignification had the opposite effect. The combined effect of hemicellulose removal and acetylation caused more than a 30% decrease of cell wall moisture content when compared with control wood. The acetylated and partially delignified wood cell walls contained higher cell wall moisture content than acetylated wood. An approximate theoretical calculation of hydroxyl accessibility for acetylated wood was in the low range, but it agreed rather well with the measured accessibility, while acetylated and partially hemicellulose-depleted and partially delignified wood for unknown reasons resulted in substantially lower hydroxyl accessibilities than the theoretical estimate.
•Endothermic differentiation allows calculating the distribution of water-filled pores.•The presented method is time saving and obtains a continuous pore size distribution.•The results are more ...reliable and close to the prediction of molecular simulations.
The pore size distribution (PSD) of cell wall is crucial for the wood, which could be investigated by the heat absorption of cell wall water upon melting. This study proposed a novel approach to characterize continuous cell wall PSD by solving the differential equation of the water amount melting inside wood obtained from the differential scanning calorimetry (DSC). Compared with the method using the isothermal process, this approach gained a more accurate PSD, and overcome the disadvantages of long-time measurement. Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) was investigated with this novel method. The results showed that the pore volume decreases sharply with the increase of pore size, and the cell wall pores above 20 nm hardly existed. The relation between cell wall pore size and volume had the similar trend between the above two methods. However, there was a quantity gap in pore volume of 9.4–52.4 times between two methods.
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