@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} } @article {1766, title = { Critical Links Governing Performance of Self-binding and Natural Binders for Hot-pressed Reconstituted Lignocellulosic Board without Added Formaldehyde: A Review }, journal = {BIORESOURCES}, volume = {13}, year = {2018}, pages = {2049-2115}, abstract = {

The production of fiberboard, particleboard, and related hot-pressed biomass products can convert small, relatively low-valued pieces of wood into valuable products. There is strong interest in being able to manufacture such products without the addition of formaldehyde, which is a health hazard during both production and use. This article reviews literature describing various challenges that need to be faced in order to achieve satisfactory bonding properties in hot-pressed bio-based board products without the addition of formaldehyde. Bonding mechanisms are examined in the form of a hypothesis, in which the strength development is represented by a chain with four links. Failure of a board is expected to occur at the weakest of these mechanistic links, which include mechanical contact, molecular-scale wetting and contact, various chemical-based linkages, and structural integrity. The most promising technologies for environmentally friendly production of hot-pressed board with use of lignocellulosic materials tend to be those that favor success in the development of at least three of the mechanistic links in the hypothetical chain.

}, author = {M.A. HUBBE and A. PIZZI and H.Y. ZHANG and R. HALIS} } @article {1750, title = { Effects of steam explosion on the characteristics of windmill palm fiber and its application to fiberboard }, journal = { EUROPEAN JOURNAL OF WOOD AND WOOD PRODUCTS }, volume = {76}, year = {2018}, pages = {601-609}, abstract = {

Windmill palm fiber (WPF) obtained from the leaf sheath was treated by steam explosion under the pressure of 2.0 MPa for 120 s to modify and improve the properties of the panels manufactured with it. For comparison, an alkali treatment and acid treatment have also been used to treat WPF. Fiber analysis, scanning electron microscopy (SEM) observation, Fourier transform infrared spectroscopy (FTIR) and chemical composition analysis showed that after the steam explosion treatment: (1) the length, width and fine elements of the windmill palm fibrils were more influenced by the steam explosion treatment than by the other two treatments. (2) A great number of spinulose spherical silica bodies and waxy layers were observed on the surfaces of all the fibers except for the steam explosion treated windmill palm fiber (SEWPF) surfaces, and (3) the cellulose fraction correspondingly increased with the decrease of the hemicelluloses and lignin contents. Finally, the SEWPFs were used to produce fiberboards, and the modulus of rupture (MOR), internal bond (IB), water absorption (WA) and thickness swell (TS) of the fiberboards were measured. The results showed that the WA and TS of the fiberboards made of SEWPF decreased 22 and 32\%, respectively, in relation to those made of WPF, whereas the IB increased 46\%. It is suggested that steam explosion can be a feasible approach to modify WPF and expand its uses.

}, author = {H. LUO and H.Y. ZHANG and L. YUE and A. PIZZI and X.N. LU} } @article {1726, title = { Energy Release Rate Measurement of Welded Bamboo Joints }, journal = { JOURNAL OF RENEWABLE MATERIALS }, volume = {6}, year = {2018}, pages = {450-456}, abstract = {

Double cantilever beam tests were used to measure the energy release rates of linear vibrational welded moso bamboo joints. The influence of the length of the preserved cracks, the different combinations of the inner and outer bamboo surfaces and the moisture content is studied herein. The experimental compliance method, which is based on linear elastic fracture mechanics and has been shown to be an ideal method, was used to analyze data with the power equation. The results show that the preserved initial crack length does not have a significant effect on the final measured energy release rate, while the moso bamboo combination does affect the properties dramatically. The welded moso bamboo joints with inner-inner surfaces have the highest energy release rate of 122 J/m(2). The average energy release of the outer-outer combination was only 102 J/m(2) . The expansion of the cracks also became easier when the moisture content of the welded joints was 18.5\% compared to 4.5\% and 10.1\%. So the moisture resistance of the welded joints should be duly improved.

}, author = {H.Y. ZHANG and Q. HE and X.N. LU and A. PIZZI and C.T. MEI and X.X. ZHAN} } @article {1774, title = { The study of linear vibrational welding of moso bamboo }, journal = { JOURNAL OF ADHESION SCIENCE AND TECHNOLOGY }, volume = {32}, year = {2018}, pages = {1-10}, abstract = {

Moso bamboo (Phyllostachys pubescens) linear-vibration welded joints with three different combinations between the inner and outer surfaces were studied in this paper. The tensile-shear strength, the microstructures and welded layer thickness observed by SEM and the density profiles measured by X-ray densitometer of the welded samples have been considered and compared. The maximum average tensile-shear strength of outer-outer, inner-inner and outer-inner welded joints were 5.91, 7.15 and 6.24MPa, respectively. And only the inner-inner welded joints have the bamboo failure after the shear test. The welded joint is composed of a lot of bamboo fibers entangled in the molten and flown intercellular materials which decide the final mechanical performance of the welded joints. The thickness of the outer-outer welded layer is the smallest and the inner-inner welded layer is the highest. However, the maximum density reached in the inner-inner welded joint is smaller than in the outer-outer welded joint owing to the different vascular distribution in the cross section of the moso bamboo. The relative density can be used to reflect the tensile-shear strength of the welded joints. The natural structure of bamboo really do have significant influences on the welded interface.

}, author = {H.Y. ZHANG and A. PIZZI and X.H. ZHOU and X.N. LU and Z.Q. WANG} } @article {1696, title = { Study of the End-grain Butt Joints Obtained by Friction Welding of Moso Bamboo }, journal = {BIORESOURCES}, volume = {12}, year = {2017}, pages = {6446-6457}, abstract = {

End-grain-to-end-grain welding has been the object of considerable study in the authors\&$\#$39; laboratory, but successful experiments have been hindered by wood defibration. End-grain butt joints obtained by friction welding with moso bamboo showed relatively good experimental results compared to beech, oak, and spruce. The average compression shear strength of the welded joints reached 5.81 MPa, and the departure of the bamboo fibers could not be observed during the welding process. A study of the microstructure of the welded surface revealed that during the welding process, hard vascular bundles within the fibers became prominent on the welded surface and acted similarly to a brush. These bundles dissipated lateral friction and protected the bamboo from cracking in the process.

}, author = {H.Y. ZHANG and A. PIZZI and X.N. LU and Z.Q. WANG} }