EQUILIBRIUM MOISTURE CONTENT UNDER VACUUM CONDITIONS

The equilibrium moisture content (EMC) of three species was measured under vacuum conditions. Temperature, RH, and ambient pressure in a chamber were controlled during the experiments to obtain accurate EMC measurement under vacuum. Based on the experimental results and on the Hailwood–Horrobin model for EMC, the desorption isotherms of wood under vacuum were analyzed.EMC charts and a database under vacuum conditions were also built. Results showed that the desorption isotherms of wood under vacuum conditions also presented a typical sigmoid shape similar to the one at atmospheric conditions. The effect of ambient pressure on EMC was small at high RH ranges and became obvious with decreasing RH. Also, the EMC of ambient pressure from 53.3 to 101.3 kPa was not obvious because the difference in EMC was only 0.1-0.4%. Conversely, the effect of pressure became greater from 53.3 to 13.3 kPa and the difference in EMC was 1.2-1.9%. EMC corresponding to temperature, RH, and ambient pressure at vacuum conditions was built with the chart and equations based on experimental results from the real-time MC measurement for vacuum drying and serves as an aid in wood research and drying control under vacuum conditions

Pseudo-Parity-Time Symmetry in Optical Systems

We introduce a novel concept of the pseudo-parity-time (pseudo-PT) symmetry in periodically modulated optical systems with balanced gain and loss. We demonstrate that whether or not the original system is PT symmetric, we can manipulate the property of t

Fabrication of densified wood via synergy of chemical pretreatment, hot-pressing and post mechanical fixation

Article describes examination of the appearance, color, chemical composition, and physiology and mechanical properties of densified Abies wood before and after densification treatment using a colorimeter, FTIR and mechanical testing machine

Pore-Rich Cellulose-Derived Carbon Fiber@Graphene Core-Shell Composites for Electromagnetic Interference Shielding

Because of serious electromagnetic pollution caused by the widespread use of radio frequency equipment, the study of electromagnetic interference (EMI) shielding materials has been a long-standing topic. Carbon fiber and graphene composites have great potential as EMI shielding materials due to their unique microstructure and electrical conductivity. In this work, a novel kind of core-shell composite is fabricated based on the pore-rich pine needles-derived carbon fibers (coded as PNCFs) core and the graphene shell. The pore-rich PNCFs are created by KOH activation, and the integration between the pore-rich PNCFs and the graphene relies on a plasma-enhanced chemical vapor deposition (PECVD) method. The conductivity of the pore-rich PNCFs@graphene core-shell composite reaches 4.97 S cm−1, and the composite has an excellent EMI shielding effectiveness (SE > 70 dB over X-band (8.2–12.4 GHz)) and achieves a maximum value of ~77 dB at 10.4 GHz, which is higher than many biobased EMI shielding materials in the recent literature. By calculation and comparison, the large absorption loss (accounting for 90.8% of total loss) contributes to reducing secondary radiation, which is quite beneficial for stealth uses. Thus, this work demonstrates a promising design method for the preparation of green high-performance composites for EMI shielding and stealth applications (such as warcrafts, missiles, and stealth wears)

Modification of Poplar Wood via Polyethylene Glycol Impregnation Coupled with Compression

Wood permeability and compressibility are affected by cell wall structure and chemical composition. These properties can be improved by appropriate wood pretreatments. Low-density poplar wood was converted to a more dense structure by the following steps: First, lignin and hemicellulose were removed using a mixture of NaOH and Na2SO3. Second they were impregnated with polyethylene glycol (PEG, mean molecular weight of 1200), nano-SiO2, and a silane coupling agent at atmospheric temperature and pressure. Finally, impregnated wood was compressed at 150 °C. Results showed that the tracheid lumens on the transverse section of the compressed wood almost vanished. Specifically, the lumens in the wood cells, especially those that were compressed, were almost completely filled with PEG. In FTIR, the asymmetric absorption peaks of Si–O–Si at 1078–1076 cm−1 were clearly observed, which confirms the existence of bonding between nano-SiO2 and wood. The highest melting enthalpy and crystallization enthalpy showed a heat storage capacity of modified wood, which were 20.7 and 9.8 J/g, respectively. Such phase change capabilities may have potential applications in regulating the rate of change of room temperature. In summary, the modified wood could be utilized as material for construction to conserve energy

Modification of Poplar Wood via Polyethylene Glycol Impregnation Coupled with Compression

Wood permeability and compressibility are affected by cell wall structure and chemical composition. These properties can be improved by appropriate wood pretreatments. Low-density poplar wood was converted to a more dense structure by the following steps: First, lignin and hemicellulose were removed using a mixture of NaOH and Na2SO3. Second they were impregnated with polyethylene glycol (PEG, mean molecular weight of 1200), nano-SiO2, and a silane coupling agent at atmospheric temperature and pressure. Finally, impregnated wood was compressed at 150 °C. Results showed that the tracheid lumens on the transverse section of the compressed wood almost vanished. Specifically, the lumens in the wood cells, especially those that were compressed, were almost completely filled with PEG. In FTIR, the asymmetric absorption peaks of Si–O–Si at 1078–1076 cm−1 were clearly observed, which confirms the existence of bonding between nano-SiO2 and wood. The highest melting enthalpy and crystallization enthalpy showed a heat storage capacity of modified wood, which were 20.7 and 9.8 J/g, respectively. Such phase change capabilities may have potential applications in regulating the rate of change of room temperature. In summary, the modified wood could be utilized as material for construction to conserve energy

Effect of H₂O₂ Bleaching Treatment on the Properties of Finished Transparent Wood

Transparent wood samples were fabricated from an environmentally-friendly hydrogen peroxide (H2O2) bleached basswood (Tilia) template using polymer impregnation. The wood samples were bleached separately for 30, 60, 90, 120 and 150 min to evaluate the effects on the changes of the chemical composition and properties of finished transparent wood. Experimental results showed decreases in cellulose, hemicellulose, and lignin content with an increasing bleaching time and while decreasing each component to a unique extent. Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) analysis indicated that the wood cell micro-structures were maintained during H2O2 bleaching treatment. This allowed for successful impregnation of polymer into the bleached wood template and strong transparent wood products. The transparent wood possessed a maximum optical transmittance up to 44% at 800 nm with 150 min bleaching time. Moreover, the transparent wood displayed a maximum tensile strength up to 165.1 ± 1.5 MPa with 90 min bleaching time. The elastic modulus (Er) and hardness (H) of the transparent wood samples were lowered along with the increase of H2O2 bleaching treatment time. In addition, the transparent wood with 30 min bleaching time exhibited the highest Er and H values of 20.4 GPa and 0.45 GPa, respectively. This findings may provide one way to choose optimum degrees of H2O2 bleaching treatment for transparent wood fabrication, to fit the physicochemical properties of finished transparent wood

Evaluation of the properties of hybrid yellow poplar (Liriodendron sino-americanum): A comparison study with yellow poplar (Liriodendron tulipifera)

As one of fast-growth wood species, hybrid yellow poplar (YP-h, Liriodendron sino-americanum) has been extensively planted throughout of China, however, little is known about its properties and applicability in structural and nonstructural applications such as construction and furniture. The aim of this study was to evaluate the properties of YP-h and examine its differences with yellow poplar (YP, Liriodendron tulipifera). The average vessel diameter of YP-h (55 μm) was 19 % lower than YP (68 μm), but, the density of YP-h was 37 % higher than YP and the dimensional change in YP-h was higher than YP. Comparable tensile strength and flexural modulus were found in YP-h and YP, however, the flexural, shear, and impact strength of YP-h was 35 %, 40 %, and 55 % higher than those of YP, respectively. The drilling, mortising, and turning processability of YP-h were superior to those of YP. Compared to the gluing and coating performance of YP, YP-h had inferior gluing properties and equivalent coating performance. Therefore, hybrid yellow poplar can be an ideal candidate for yellow poplar to be utilized in construction and furnitur