@article {1859, title = { Effect of vacuum hot pressing on the bonding quality and heat transfer performance of plywood }, journal = { EUROPEAN JOURNAL OF WOOD AND WOOD PRODUCTS }, volume = {78}, year = {2020}, pages = {441-447}, abstract = {

Vacuum technology was applied to the hot-pressing technology of plywood production with phenolic resin (PF). For plywood with the same number of layers, veneers were hot-pressed with conventional and vacuum hot-pressing processes respectively at the same hot-pressing time. Varying layers (3, 9 and 15-layers) and spread quantities (220 g m(-2), 260 g m(-2), 300 g m(-2)) were applied. Heat transfer performance of the assembly, polymerization extent of PF, and bonding quality of plywood were examined by thermocouple and humidity sensors, Fourier transform infrared spectroscopy (FTIR), fluorescence microscope and bonding strength measurement. The results indicated that, compared to conventional hot pressing, the temperature of the central layer of the assembly vacuum hot-pressed was significantly increased by about 20-30 degrees C and the adhesive cured more quickly. The hot-pressing method had a significant influence on the bonding strength of plywood, with an enhancement of the bonding strength to wood failure ratio of 48.37\% and 33.55\%, respectively. The adhesive between adjacent laminates formed a continuously dense layer with more connection points, leading to excellent mechanical meshing and high bonding quality. In addition, vacuum hot pressing can eliminate the influence of adhesive position on bonding strength and make the mechanical properties of plywood tend to be uniform in thickness direction. Under the experimental conditions, the variable energy cost of 15-ply plywood with 1 m(3) produced by vacuum hot pressing was 3.83\% less than that of conventional hot pressing, and the plywood could still maintain good bonding strength at low spread quantity.

}, author = {L. HONG and Q. HE and Z.H. JU and H.Y. ZHANG and N. BROSSE and X.N. LU} } @article {1846, title = { Facile preparation of high anti-fungal performance wood by high voltage electrostatic field (HVEF) }, journal = { JOURNAL OF CLEANER PRODUCTION }, volume = {260}, year = {2020}, abstract = {

In this study, in order to improve the anti-fungal performance of wood material, a facile, efficient and eco-friendly method was proposed for wood modification under the synergistic effect of silver particles and high voltage electrostatic field (HVEF) treatment. Poplar wood, a vulnerable to decay species, was hot-pressed by silver electrode plates and exposed simultaneously to HVEF. The chemical characteristics and anti-fungal performance of treated wood were investigated in details. Under HVEF treatment, silver particles were triggered to different oxidized forms and bound with polar groups in the wood cell wall. Decreased O/C element ratio and -OH groups and increased C-H and C=O bonds in treated wood were observed by the X-ray photoelectron spectra (XPS) and fourier transform infrared (FTIR) spectroscopy. After 24h of HVEF treatment, high concentration (10.71\%) of well-distributed silver particles appeared in mapping graphs. Laboratory anti-fungal tests showed that mass losses of treated wood samples decreased significantly (\<1\%) after exposing to rot fungi. The highest leaching percentage of silver in treated samples was 3.94\%. These results indicated that the synergistic effect of silver particles and HVEF treatment enhanced the fungal-resistance performance of wood. Moreover, this approach could be regarded as a facile, efficient and eco-friendly modification to broaden the outdoor-use potential of wood.

}, url = {https://hal.univ-lorraine.fr/hal-02508085}, author = {Q. HE and T.Y. ZHAN and H.Y. ZHANG and Z.H. JU and L. HONG and N. BROSSE and X.N. LU} } @article {1843, title = { Influence of high voltage electrostatic field (HVEF) on bonding characteristics of Masson (Pinus massoniana Lamb.) veneer composites }, journal = { EUROPEAN JOURNAL OF WOOD AND WOOD PRODUCTS }, volume = {77}, year = {2019}, pages = {105-114}, abstract = {

For the first time, it was experimented with high voltage electrostatic field (HVEF) for the optimization of the bonding process of urea formaldehyde (UF) resin to wood. Varying HVEF treatment times (0-8min) and intensities (5-20kV) were applied. Wood surface characteristics, polymerization extent of UF, and bonding interphase of UF to wood were examined by electron spin resonance (ESR) spectroscopy, dynamic contact angle goniometers, Fourier transform infrared spectroscopy (FTIR), X-ray densitometer, fluorescence microscope and bonding strength measurement. The results indicated that HVEF treatments applied to wood veneer induced a decrease in contact angles and an increase in the free radicals of wood, and surface energy varied with treatment times and intensities. These varieties were because triggered free electrons, broken chemical bonds and new ions appeared on the wood surface with HVEF treatment. An aggregated performance was obviously obtained in micrographs and vertical density profiles (VPDs). It was explained that resin penetration into wood structure was significantly shallow, and resin concentration and density at bonding interphase were more enhanced than the control. This is due to the increment of surface energy and lower contact angles providing more chances for possible reactions of wood surface with the UF resin. Resin penetration depth and density varied with different treatment times and intensities. Increased cross-linking extent of UF was obtained under varied conditions of HVEF treatment. The bonding strength was measured as a function of treatment times and intensities respectively; it increased by 85\% and the wood failure ratio significantly increased by 70\% under HVEF treatment (20kV, 8min) due to the aggregation performance and more cross-linked UF resin. It was manifested that both treatment time and intensity play a significant role in HVEF treatment, and HVEF treatment has a significant influence on the characteristics of the wood surface and the bonding properties of wood composites.

}, url = {https://hal.univ-lorraine.fr/hal-02289753}, author = {Q. HE and T.Y. ZHAN and Z.H. JU and H.Y. ZHANG and L. HONG and N. BROSSE and X.N. LU} } @article {1795, title = { Robust and durable bonding performance of bamboo induced by high voltage electrostatic field treatment }, journal = { INDUSTRIAL CROPS AND PRODUCTS }, volume = {137}, year = {2019}, pages = {149-156}, abstract = {

To enhance the bonding performance of bamboo, the high voltage electrostatic field (HVEF) treatment was used for flattened moso bamboo (Phyllostachys pubescens). Three bonding types including bamboo skin-bamboo skin (BS-BS), bamboo skin-bamboo pith (BS-BP) and bamboo pith-bamboo pith (BP-BP) were tested. Surface characteristics of HVEF-treated bamboo composites were analyzed by the electron spin resonance (ESR), X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FTIR), fluorescence microscopy and vertical density profile (VDP). Mechanical properties, including bonding strength, modulus of rupture (MOR), modulus of elasticity (MOE) and boiling peeling rate of treated-bamboo composites were tested as well. The results of ESR, XPS and FTIR showed that significantly increased free radicals, broken chemical bonds and oxygen-containing groups (-OH, C=O and C-O) were obtained. These variations were attributed to the fact that triggered electrons were able to break oxygen and water molecules in the atmosphere under HVEF treatment and more broken chemical bonds (oxygen atoms and ions) appeared and reacted with bamboo surface. Higher change ratios involved in BS compared with BP were due to higher components of cellulose and lignin. HVEF treatment induced a significant decrease on adhesive penetration depth and an increment on density at bonding interphase. The highest decrease of adhesive penetration depth and increment of density at bamboo interphase were obtained in BS-BS while the least was BP-BP. All the bonding performance significantly enhanced after HVEF-treatment. The most robust and durable bonding performances were obtained in BS-BS type, and BP-BP showed the most increment extents of bamboo failure ratio. Results of this study revealed that: HVEF treatment was an effective approach for enhancing bonding properties of both bamboo skin and pith.

}, url = {https://hal.univ-lorraine.fr/hal-02289743}, author = {Q. HE and T.Y. ZHAN and H.Y. ZHANG and Z.H. JU and L. HONG and N. BROSSE and X.N. LU} }