Volume 15 Issue 2

The thermal conductivity and the deformation of wood from the Taxodium hybrid ‘Zhongshanshan’ were studied in the process of heat transfer. The results showed that the average thermal conductivity of this wood was 0.1257 W/(m·K) under the condition of 12% wood moisture content and 30 °C heat transfer temperature. When the testing temperature exceeded 0 °C, the thermal conductivity increased linearly with both temperature and wood moisture content and was affected by the moisture content of the wood. During the heat transfer process, the deformation of features caused repeated swelling and shrinkage in the longitudinal, radial, and tangential directions. The dimensional change was greatly affected by the wood’s moisture content and was less affected by the temperature. These results are of great meaning for the study of the heat transfer process of Taxodium hybrid ‘Zhongshanshan’ wood. Furthermore, it provides a scientific basis for the heat preservation effect, drying treatment, and pyrolysis treatment of Taxodium hybrid ‘Zhongshanshan’ wood for use as a building material.

In the process of applying the high-frequency heating technology to bamboo heat treatment, controlling the material temperature has a great influence on the quality of bamboo forming. Therefore, research on the heat transfer mechanism of high-frequency heating of arc-shaped bamboo pieces is of great importance. In this paper, the influence of different moisture content, chord length, and plate voltage on the heating rate of arc-shaped bamboo pieces under high-frequency electric field were studied. The moisture content of bamboo had the most remarkable effect on the heating rate. With increased moisture content, the temperature rose faster. The selection of the plate voltage had an obvious influence on the heating. If the voltage was low, the heating rate was too slow, the heating time was long, or the voltage was high, it was easy to cause electric field breakdown and damage the bamboo pieces. As the chord length decreased, the heating rate gradually increased. When the radian of the arc-shaped bamboo pieces could be ignored, the heating rate was the fastest. The results showed that under certain conditions, the arc-shaped bamboo pieces showed a good heat treatment effect in a high-frequency electric field.

The choice of optimal pressing regime for certain types of substrate is of great importance in production of veneered panels. In this paper, the impact of pressing regime on the bonding strength of beech and oak veneers, glued with urea-formaldehyde (UF) adhesive, on medium-density fiberboard (MDF), and moisture-resistant MDF (MR MDF) substrates was examined. The analyses showed a generally higher bond strength with oak veneer compared to beech veneer, which was also the case with regular MDF compared to moisture-resistant MDF. Multivariate analysis of variance (ANOVA) showed that with beech veneer, all of the used regimes produced better results on regular MDF compared to moisture-resistant MDF. In contrast, with oak veneer, the influence of pressing regime had a more noteworthy impact than the type of substrate used. These results indicated that the use of MR MDF as substrate in combination with UF adhesive was inadequate.

Physical and mechanical properties were evaluated for industrial and laboratory boards intended to be used in the construction industry. The boards were subjected to accelerated aging tests including resistance to humidity in the conditions of cyclic test in accordance with EN 321 (2002), and determination of dimensional changes resulting from changes in relative humidity according to EN 318 (2002). The greatest changes were observed after one test cycle. Moreover, the boards made of fine chips demonstrated slightly higher resistance to the tested factors. Although laboratory boards showed a much lower density, their behavior following the exposure to the assessed factors was similar to that of industrial plates.

The deformation behavior of high-pressure (HP)-treated hybrid poplar wood, the subsequent swelling, and the equilibrium moisture content properties of HP-densified wood were evaluated using a modified delayed strain/set-recovery method of cyclic humidification-dehumidification at different relative humidity (RH) conditions. The HP treatment resulted in significant compression (densification) of the wood under different treatment conditions. For treated wood samples, the value of delayed elastic strain was relatively small when stored at 20 °C and 65% RH, which indicated that HP-densified wood possessed dimensional stability. The HP-compressed poplar yielded lower equilibrium moisture content than the control at low RH, while major increases were observed at high RH above 76%. Marginal of thickness swelling was observed under the cyclic humidification-dehumidification method in the low RH range while significant swelling occurred at high RH. Conventional methods would only show results that were appropriate for storage at high RH environments. The RH threshold for set-recovery of HP-compressed wood was between 33% and 54% for optimal use, and the extent of set-recovery increased rapidly when RH was between 85% and 95%. Such differences could not be recognized with the conventional methods. In addition, the prolonged holding time significantly decreased the RH threshold value (P < 0.05).

Heat treatment is an environmentally friendly and efficient way to improve the properties of wood species. These treatments alter the substrates and can influence the surface properties of the varnish coatings. This paper investigated the effects of heat treatment on the physical properties of open and close systems Scots pine (Pinus sylvestris L.) and poplar (Populus euramericana) wood, coated with water-based, polyurethane-based, and oil/wax-based varnishes. Heat treatment was applied at the temperatures of 190, 212 °C for pine and 180, 200 °C for poplar, respectively. Color, gloss, and roughness tests were carried out for each of the coatings. Higher mass loss occurred in pine samples with heat treatment as compared to vacuum-heat treatment. Gloss decreased in OIL+WAX treatment and color change increased after the heat treatment, but these results were inhibited with vacuum-heat treatment. Maximum roughness was obtained in PUR varnishes and minimum roughness in OIL + WAX samples. The low roughness values provide some advantages in application.

The degradation processes of tannin and saponin were studied during co-composting of the shell and seed cake of Camellia oleifera Abel. Four treatments were designed, with the dry weight of the seed cake accounting for 30% (A1), 25% (A2), 20% (A3), and 10% (A4) of the shell weight. During the composting, the duration and the highest temperature of the thermophilic phase were positively correlated with the addition proportion of seed cake. The degradation rates of tannin and saponin were positively correlated with the addition proportion of seed cake, but the C/N ratio and final tannin content were negatively correlated with it. The saponin content ultimately contributed to approximately 2% of the final compost mass. The final content of saponin and tannin decreased by 68.9 to75.2% and 34.6 to 59.5%. The organic matter and total nutrient content (N, P2O5, and K2O) increased with the increasing proportion of seed cake. An addition proportion of 30% of Camellia oleifera seed cake is recommended to produce homogenous compost. Overall, the addition of the seed cake promoted the maturity, fertilizer quality, and safety of the co-compost product.

The application of cellulose materials for packaging usage has attracted a large amount of attention in recent years. In this study, cellulose was dissolved in a cold NaOH/urea solution. Transparent, strong, and flexible regenerated cellulose/polyvinyl alcohol (PVOH) films were fabricated via a solution blending and casting process. The physicochemical properties of the neat RC films, PVOH films, and RC-PVOH blend films were characterized via scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, tensile tests, gas permeability, and ultraviolet-visible spectroscopy. The results of the physicochemical characterizations indicated that the RC-PVOH composite films with various PVOH contents yielded strong properties in terms of optical transparency, thermal stability, mechanical strength, and oxygen barrier performance. The RC-PVOH films with 8% PVOH loading exhibited a peak degradation temperature of 362 °C, a tensile strength of 80.8 MPa ± 0.3 MPa, and an oxygen permeability of 2.40 cm3 x μm/m2 x 24 h x kPa. The RC-PVOH composite films could be a competitive alternative as a packaging material to replace petroleum-based plastics.

This study inspected the thermal decomposition kinetics of core-shell structured wood-plastic composite material with white mud loading in the shell. The thermal decomposition was studied via thermogravimetric analysis under nitrogen atmosphere. Experiments were performed at different heating rates of 5, 10, 20, 30, and 40 °C/min from ambient temperature to 700 °C. Multivariate linear regression analysis was applied to estimate the activation energy with the Flynn–Wall–Ozawa method, and the thermal aging life equations of composites were obtained as described in ASTM E1877 (2000). The results showed that the combustion characteristic parameters (T5%, Tp1, Tp2, and Tp3) increased at first and then decreased with increased white mud concentration. Accordingly, the average apparent activation energy (Ea) values of thermal decomposition with conversion rates ranging between 20% and 80% were 222 kJ/mol for high-density polyethylene (HDPE) shell layer and the average values of 201, 226, 201, 207, and 223 kJ/mol were achieved with white mud loading of 5, 10, 15, 20, and 25% in the shell layer, respectively. There were no remarkable dependencies among them. The service life tf (min) and the service temperature T (K) of the core-shell structured wood-plastic composites were experimentally determined.

The functional design of ultrasonic sonotrodes for deep-drawing is considered. The achievable stability, shape deviation, and surface roughness of deep-drawn cups were determined as a function of the vibration mode, the vibration amplitude, and the contact pressure as it occurs in the gap between the tools. Because the development of sonotrodes is complex and expensive, substitute experiments were conducted that allowed the cup parameters to be determined even without the manufacture of numerous sonotrodes, thus minimizing the effort involved. The results showed that the vibration mode, which determines the angle at which the vibration hits the material surface, is the most important influencing factor. The best way to increase stability and reduce shape deviation and surface roughness is to use an oscillation that hits the material surface perpendicularly during the entire deep-drawing process. With perpendicular vibration, the strength of the cup wall increased up to 200% compared to the one produced without ultrasound. The surface roughness could be reduced to 50% with the vertical vibration compared to without ultrasonic support.