Zhangjing Chen

Theoretical exploration of factors affecting dielectric constants of masson pine

Abstract A theoretical model to calculate the dielectric constant of masson pine (Pinus massoniana) in the longitudinal direction was developed by considering the effect of wood moisture content, density, ratio of earlywood to latewood, and the volume fraction of ray cells. The calculated results were used to explore the relationship between dielectric constant and moisture content, density, and other factors. The results indicated that the dielectric constant of masson pine increased with the moisture content. From 0% to 30% moisture content, the longitudinal dielectric constant increased more than 5 times from 2.3 to 13.3. In the range of density from 0.450 to 0.650 (g cm−3 at 15% moisture content, the longitudinal dielectric constant increased from 7.7 to 10.0. However, the longitudinal dielectric constant decreased as the volume fraction of ray cells increased.

Thermogravimetric analysis of cork and cork components from Quercus variabilis

Cork and cork components (suberin, lignin, holocellulose, sclereids, and lenticels) were obtained by manual and chemical methods. Dynamic thermogravimetric analysis was used to investigate the thermal behavior of cork and its components. Thermal decomposition of cork was different from that of natural fibers. Characteristic temperatures of thermal decomposition for cork and impurities (sclereids and lenticels) were related to their chemical components. Cork lignin has the decomposition characteristics of G-type (guaiacyl units) lignin, typical of softwood with high residual solids. The pyrolysis characteristics of Quercus variabilis Blume (Q. variabilis) suberin was close to Quercus cerris L. (Q. cerris) suberin. The decomposition temperature range of cork, lignin, or suberin was wider than that of sclereids, lenticels, or holocellulose. Activation energy of cork was lower than that of natural fibers. The activation energy of cork and the extracted suberin was slightly increased when the conversion rate α was greater than 0.35. Activation energies of sclereids and lenticels were close to each other due to similar composition and proportion in them.

Preliminary study of Cell Wall Structure and its Mechanical Properties of C3H and HCT RNAi Transgenic Poplar Sapling

This research focused on the cell wall structure and its mechanical properties of down-regulated Coumaroyl shikimate 3-hydroxylase (C3H) transgenic poplar and down-regulated hydroxycinnamoyl CoA: shikimate hydroxycinnamoyl transferase (HCT) transgenic poplar (Populus alba × P. glandulosa cv ‘84 k’). The wood samples with respect to microstructure, the longitudinal elastic modulus (MOE) and hardness of wood fiber secondary cell wall were investigated. The results show that the lignin contents in the two transgenic poplar woods were lower than non-modified wood. The C3H transgenic poplar and HCT transgenic poplar have more than 18.5% and 16.1% cellulose crystalline regions than non-modified poplar respectively. The diameter of the fiber cell and the vessel element of transgenic poplars are smaller. Double radial vessel cell wall thicknesses of both transgenic poplars were smaller than non-modified poplar. Cell wall ratios for the transgenic poplar were higher than non-modified poplar and cell wall density was significantly lower in both C3H and HCT transgenic poplar. The cell wall MOEs of C3H and HCT transgenic poplar was 5.8% and 7.0% higher than non-modified poplar. HCT can be more effective than C3H to modify the trees by considerably increasing mechanical properties of the cell wall.

Bonding performance of melamine-urea-formaldehyde and phenol-resorcinol-formaldehyde adhesives in interior grade glulam

Abstract Wood moisture content (MC) affects the glued laminated beam (glulam) bonding strength. Selected adhesives were Phenol-Resorcinol-Formaldehyde (PRF) and Melamine-Urea-Formaldehyde (MUF) adhesives with 1, 1.5 and 2% (w/w) carboxymethyl cellulose (CMC) formic acid solutions. Douglas fir (pseudotsuga menziesii) from North America was used in the test. The bonding behavior of these adhesives with wood at 12 and 18% MC were investigated. The study focused on the effect of 18% MC on shear strength performance of MUF and PRF adhesives and optimizing the formula of CMC formic acid solution. Compressive shear strength of wood with MUF adhesive with 2% (w/w) formic acid solution at 12 and 18% MC stabilized at 10.6 and 10.0 MPa, respectively, which were 17 and 16% higher than that with PRF adhesive at the same condition. At 12–18% MC, MC had a little effect on bonding strength. However, 18% MC wood with PRF adhesive had 52.2% less initial strength increasing rate than that of 12% MC wood. 18% MC wood with MUF adhesives with 1, 1.5 and 2% (w/w) CMC formic acid solutions had 16.0, 15.5 and 27.0% less initial strength increasing rates than that of 12% MC wood, respectively. MUF adhesive using 2% CMC formic solution required the shortest press time at 12 and 18% MC about 1.6 and 2.7 h, respectively. The strength of PRF adhesive was significantly affected by wood MC and enough press time is essential for the proper bonding strength.

Theoretical Determination of Thermogravimetric Model of Oak Cork (Quercus variabilis) using Málek Kinetic Analysis

Abstract The purpose of this study was to determine the expression of a kinetic model and the determination of kinetic parameters for cork. Thermal analysis kinetics of cork and impurities (sclerei...