Preparation and characterization of conductive and corrosion-resistant wood-based composite by electroless Ni–W–P plating on birch veneer

A conductive and corrosion-resistant wood-based composite was obtained via electroless Ni–W–P plating on birch veneers. The W content of the Ni–W–P coatings obtained under different Na₂WO₄ concentrations in the plating bath was analyzed. The crystal structure, surface morphology, electrical resistivity, electromagnetic shielding effectiveness, surface wettability, adhesive strength and corrosion resistance of the composite were investigated. Energy-dispersive spectroscopy and X-ray photoelectron spectroscopy results showed that the coating consisted mainly of Ni⁰, Mo⁰ and P⁰ doped with little of their oxides. X-ray diffractometry analysis suggested the obtained coatings contained a nanocrystalline structure. Scanning electron microscopy images showed that the veneer surfaces were covered with uniform and continuous coatings. Birch veneers plated with Ni–W–P alloy exhibited good electrical conductivity with surface resistivity below 200 mΩ/cm² and shielding effectiveness above 35 dB from 9 kHz to 1.5 GHz. Ni–W–P films firmly adhered to the wood surface. Water contact angle of the composite reached about 130° indicating the hydrophobic surface. The Ni–W–P-plated veneers showed excellent corrosion resistance due to the polarization resistance above 3.1 kΩ/cm². This study further provides a new method for fabricating multifunctional wood-based composites.     

A new quantitative method for evaluation of adhesive penetration pattern in particulate wood-based composites: elemental counting method

The importance of adhesion in production of wood-based composites is well-known. Adhesive penetration and interphase morphology play an important role in bond strength and product performance. Many studies offered different methods for interphase characterization and analysis. Both qualitative and quantitative methods have been used to analyze the bondline. Most of the quantitative methods were developed for bonded assemblies of veneer or wood blocks. Adhesive penetration measurement in particulate wood-based composites is the main scope of this study. For this purpose, uniform oriented strand board with veneer strands was produced by the use of phenol formaldehyde resin with 2, 6, and 10 % strand moisture content (MC). The strands were formed into well-organized mats to achieve a uniform structure for the composite. Cross-section specimens were prepared from each board and observed by epifluorescence microscopy. Six positions for growth-ring angle in adhesive joints were denoted to evaluate penetration in different directions of the wood. Four parameters were also determined to quantify resin penetration patterns by counting the quantity of the main anatomical elements of wood, which were filled with resin. Finally, it was determined that this method could recognize the differences between adhesive penetration in boards produced with different level of strand MC. Resin penetration in strands with 6 and 10 % MC was the greatest. Growth-ring angle of the strands influenced penetration as it was increased when both strands meet each other in an oblique position, although this effect was significant only in maximum penetration depth in fibers.     

Thermal treatment of sawdust and coal-tar pitch mixture to produce porous carbon materials by chemical activation

In this work, different activated carbons were prepared from composites based on birch sawdust and coal-tar pitch by chemical activation with zinc chloride, phosphoric acid, and potassium hydroxide followed by carbonization. The influence of different chemical agents (ZnCl₂, KOH, and H₃PO₄), final temperature of carbonization and media on yield and structural properties of the carbonic product was studied. It was shown that chemical agents allow increasing yield of carbonic residue. Composite modification by H₃PO₄ or ZnCl₂ facilitates the formation of molded porous carbonic residue during the carbonization process. However, addition of KOH to the composite leads to formation of powder-like carbonic residue having a specific surface area of 1,600 m² g^?1 at 800 °C. It was established that all samples aged in air medium at 800 °C have higher values of specific surface area in comparison with the same samples aged in argon medium at similar conditions.     

Effect of thermomechanical densification on surface roughness of wood veneers

The effect of short-term thermomechanical densification of veneer on the surface roughness and surface anatomical changes in four wood species – alder (Alnus glutinosa Gaertn.), beech (Fagus sylvatica L.), birch (Betula verrucosa Ehrh.), and pine (Pinus sylvestris L.) – was studied. Veneer sheets were densified at a temperature of 100, 150, or 200°C and at a pressure of 4, 8, or 12 MPa for 4 minutes. Seven roughness parameters such as R_a, R_z, R_q, R_p, R_v, R_sk, and R_ku were determined. Profile surface was recorded using a modified Carl Zeiss ME-10 profile gauging profilometer. Surface anatomical changes of veneer were examined using scanning electron microscopy. The results showed that densification temperature and pressure affect surface roughness of veneer. The surface became smoother, and roughness values decreased significantly (except for R_ku which increased slightly) with increasing temperature and pressure of densification. The effect of temperature on surface roughness changes is more pronounced compared with that of densification pressure. The lowest values of surface roughness were recorded for pine veneer samples followed by alder, birch, and beech samples. These results can be used to provide initial data for adhesive application processes in woodworking industry.     

Seasonal dynamics and impact factors of urban forest CO<Subscript>2</Subscript> concentration in Harbin,China

CO₂ concentrations in different plant communities (larch, birch, lilac, and grassland) were measured during the growing season in the Heilongjiang Forest Botanical Garden to study diurnal variation, seasonal and annual dynamics and factors that impact CO₂ concentration in different spaces. CO₂ concentration in different communities in green lands had an obvious diurnal variation, chronically decreasing, and temperature influenced the lilac area and the grassland. Seasonally, CO₂ was lowest in the larch green land (344.03 ± 23.03 μmol/mol) and highest in the grassland (360.13 ± 22.43 μmol/mol). The overall trend in CO₂ concentration was autumn > spring > summer; temperature is the main factor controlling variation in CO₂ concentrations during the growing season; the CO₂ concentration at the larch, birch, lilac, and grassland types of sites was negatively correlated with land surface temperature and air temperature, and the CO₂ concentration at the larch and birch sites was positively correlated with atmospheric pressure. Without any obvious annual change law, further study and observation are needed.     

微纳纤丝改性豆胶制造染色杨木胶合板

将不同微纳纤丝添加量的三聚氰胺树脂涂饰在杨木单板表面,并以添加微纳纤丝的豆胶作为胶黏剂,制造杨木胶合板,检测微纳纤丝添加量对染色杨木单板表面色牢度、胶合板表面耐磨性能、胶合强度的影响。结果表明:微纳纤丝可明显改善单板表面色牢度及表面耐磨性能;在豆胶中加入微纳纤丝,可提高胶合板的胶合强度。     

单板/HDF复合木地板的制造工艺与产品性能研究

单板/高密度纤维板(HDF)复合木地板结合了实木地板和浸渍纸层压木质地板的优点,是地板产业发展的新方向之一。文中以12mm厚HDF为基材、复合意杨单板,试制了"耐磨纸-单板-HDF基材-平衡纸"四层结构地板用复合板材。研究了不同单板厚度、胶黏剂种类(聚氨酯-PU,脲醛树脂-UF)及涂布量对板材翘曲度、吸水厚度膨胀率、内结合强度及机加工性能的影响。结果表明:1)单板与HDF复合制造木地板是可行的;2)复合木地板的翘曲度随单板厚度和施胶量的提高而递增,最高可达约0.6%;3)贴面采用聚氨酯胶黏剂,产品性能优于脲醛树脂胶合板材,但冷压周期偏长。推荐工艺条件为:单板1.2mm,PU或UF胶黏剂均可,涂布量控制在100g/m~2左右。     

Simultaneous drying and densification of silver birch (Betula pendula L.) veneers: analysis of morphology,thickness swelling,and density profile

In this study, birch (Betula pendula L.) veneers were simultaneously densified and dried using a contact drying method at pressures of 1.5 and 3 MPa at 130 °C and compared with veneer dried in a laboratory-scale convective type dryer. Compression rate, thickness swelling, and the density profiles of the veneers were investigated. Furthermore, the microstructure of densified veneers was studied by scanning electron microscopy (SEM). A maximum veneer compression rate of 9 % was achieved at a pressure of 3 MPa. Under these conditions, the veneers were, on average, densified from 504 to 574 kg m^?3 (approximately 14 %). After water soaking, full set-recovery—recovery to the initial thickness—occurred. However, the swelling rate was lower for the densified veneer. Density profiles measurements showed that densification occurs throughout the veneers. The SEM images showed that the surface of the densified veneers were smoother, whilst no cracks were detected due to densification. Densification seemed to occur in vessels. Typically, rays were bent when there was a vessel nearby.     

Changes in bamboo fiber subjected to different chemical treatments and freeze-drying as measured by nanoindentation

The effects of chemical treatments (H₂O₂ + CH₃COOH, acidified NaClO₂, and NaOH) and freeze-drying on bamboo fibers were studied at a submicron level, to characterize chemical and mechanical changes to the secondary cell wall. Specifically, a field emission environmental scanning electron microscope (FE-ESEM) and imaging fourier transform infrared spectroscopy (FTIR) were used to demonstrate degradation in morphology and molecular structure, and nanoindentation was used to track changes in micromechanical properties. The results showed that cellular structures after chemical treatments clearly displayed wrinkles, pores, and microfibrils. The decreased bands at 1508 cm^-1 and 1426 cm^?1 showed that lignin was degraded on treatment of H₂O₂ + CH₃COOH and acidified NaClO₂, which directly resulted in a decrease in hardness (H) in the secondary cell wall for treated fibers. In addition, a diminishing peak at 1733 cm^?1 caused by NaOH solution indicated that hemicellulose was seriously degraded. It resulted in a decreased modulus (E _r) by 13.71 % in bamboo fibers, while no obvious reduction was observed in the first two steps.     

Shear strength development of the phenol–formaldehyde adhesive bond during cure

The development of the shear strength of the phenol–formaldehyde (PF) adhesive bond during curing was investigated. Five different PF adhesive mixtures and 1.1 mm thick peeled beech (Fagus sylvatica L.) veneer were used to produce lap-shear specimens, which were cured at a pressing temperature of 160°C. Dielectric analysis (DEA) and modified ABES (automated bonding evaluation system) were used to evaluate the physical–chemical and mechanical aspects of PF adhesive cure in a miniature hot-press. The degree of cure, which was calculated from conductivity data, was dependent on pressing time and the composition of the PF adhesive. An addition of rye flour to the PF adhesive significantly postponed the curing process as determined by DEA. It was found that the adhesive bond started to develop in the last stage of the curing (vitrification), by which time most of the physical–chemical conversion of the adhesive had been completed.     

Acceleration of the cure of phenolic resin adhesives VII: Influence of extractives of merbau wood on bonding

The influence of merbau wood extractives on the gelation rate of a phenolic adhesive and the effects of some cure accelerators on the bond performance of merbau plywood were investigated. The addition of merbau wood extractives slightly increased the gelation rate of the phenolic resin. This increase in the gelation rate was revealed to be due to a fall in the resin pH caused by addition of the extractives. The addition of cure accelerators, sodium carbonate and propylene carbonate, caused a considerable reduction in the hot-pressing time required for the merbau plywood to achieve sufficient bond qualities. Brushing veneer surfaces caused an increase in bond qualities. The combination of the cure acceleration and the surface brushing greatly improved the bondability of merbau wood. The main factor of gluing difficulty is considered to be the poor wettability of the veneer surfaces resulted from the accumulation of migrating extractives.Part of this work was presented at the 47th annual meeting of The Japan Wood Research Society, Kochi, April 3–5, 1997     

Adhesive performance of woods treated with alternative preservatives

The extended use of woods treated with traditional or alternative preservatives for exterior applications requires an assessment of wood adhesive performance. This study attempts to evaluate the performance of wood adhesives for woods treated with various waterborne preservatives. Two softwood species, i.e. Korean pine (Pinus koraiensis Sieb. et Zucc.) and Japanese Larch (Larix leptolepis [Sieb. et Zucc.] Gordon) were treated with copper–chrome–arsenic (CCA), CB-HDO, or copper azole (CY), and then bonded with four different wood adhesives such as urea–melamine–formaldehyde (UMF) resin, melamine–formaldehyde (MF) resin, phenol–formaldehyde (PF) resin, and resorcinol–formaldehyde (RF) resin. The performance of these adhesives was evaluated by measuring the dry shear strength of adhesive-bonded wood block on compression. Both UMF and MF resins produced a relatively strong adhesive strength for CY-treated pine and larch woods. The PF resin also produced good bond strength when bonded with either larch wood treated with CY or pinewood treated with CB-HDO. The best result was obtained when the CB-HDO-treated woods were bonded with RF resin. For a better bond strength development, a proper combination of adhesive, preservative, and wood species should be selected by taking into consideration of the characteristics of these three parameters as well as their interactions.     

抗菌型饰面人造板的研究

研究纳米二氧化钛(TiO2)浆料以及以纳米TiO2浆料为抗菌剂的饰面人造板的制备工艺,检测在三聚氰胺甲醛树脂(MU)中添加纳米TiO2浆料制成的饰面人造板的抗菌与物理力学性能.结果表明:以聚丙烯酰胺为分散剂,聚乙二醇和辛基酚聚氧乙烯醚为润湿剂,聚乙烯吡咯烷酮(PVP)为稳定保护胶,在高速搅拌下制成的纳米TiO2浆料,在透射电镜下观察发现纳米TiO2颗粒分布均匀,具有良好的分散性,浆料经热水浴处理,TiO2基本未出现团聚,具有较好的贮存稳定性;在MU中添加纳米TiO2浆料调制的胶粘剂,其相容性好,且不影响其胶合性能;加入纳米TiO2的浸渍纸和浸渍单板具有明显的抗菌性,当MU胶粘剂中TiO2加入量为1%时,饰面人造板具有较好的抑菌效果,它对金黄色葡萄球菌和大肠杆菌均有良好的抑制作用.     

Surface quality sensing of trembling aspen (Populus tremuloides Michx.) veneer products by near infrared spectroscopy

Abstract

The potential of near infrared spectroscopy (NIRS) to estimate wood moisture content (MC), surface energy characteristics and adhesive bond strength were evaluated on aspen (Populus tremuloides Michx.) veneer subjected to different drying times. For samples dried progressively at 103°C, the best MC prediction model was for the total MC range (0–100%) with an R² value of 0.68. However, exposure at 180°C produced surface colour changes, and the CIE L*a*b* colour parameters measuring colour changes were better estimated using the 400–900 nm spectral data than the 1100–2400 nm spectral data. Increased exposure time at 180°C resulted in lower wettability and, hence, larger contact angles, especially when ethylene glycol was used as probe solvent. Lap shear strength tests on veneers showed that adhesion by phenol formaldehyde resins was impaired by the high temperature exposure; however, the lap shear strength test had high variability so there was not always a clear relationship between contact angle and lap shear strength test.     

Gluability of thermally modified beech (Fagus silvatica L.) and birch (Betula pubescens Ehrh.) wood

Abstract

One of the main disadvantages of wood is hygroscopicity resulting from its polar character. The sorption–desorption of water causes unwanted swelling and shrinkage in wood. Thermal modification substantially reduces this inconvenient feature. Unfortunately, the same chemical changes that reduce water sorption alter the polar character of the material and result in poorer wetting of thermally treated wood by waterborne adhesives. Gluability of thermally modified beech (Fagus silvatica L.) and birch (Betula pubescens Ehrh.) wood with two commercial amino resins, melamine–urea–formaldehyde (MUF) and melamine–formaldehyde (MF), and a two-component polyurethane (PUR) adhesive was investigated. Both wood species were modified according to two temperature regimes: 160°C and 190°C. Shear strengths of the joints were then determined according to EN 205:2003 standard. The results showed that thermally modified beech and birch wood can be effectively glued not only with commercially available PUR adhesives, but also with aqueous MF and MUF resins. The resultant shear strengths of the joints were limited by the strength of the thermally modified substrate.     

CaCO<Subscript>3</Subscript> in situ treated bamboo pulp fiber reinforced composites obtained by vacuum-assisted resin infusion

The aim of this study is to investigate the properties of CaCO₃ in situ treated bamboo pulp fiber (BPF) composites that have been filled with epoxy resin by means of vacuum-assisted resin infusion (VARI). Un-treated and treated BPF were processed at a pressure of 0.24 MPa into BPF preforms. VARI was used to infuse epoxy resin through the BPF preforms to make BPF composites. The flexural properties, impact property, and thermal properties of the BPF composites were analyzed. CaCO₃ with the loading of 30 wt% affects the performance of the composites. The flexural strength did not decrease and modulus of the treated BPF composites increased by 9.38%, while the impact strength decreased by 50.98%, compared to the control sample. Dynamic mechanical analysis revealed the maximum elastic moduli of the treated specimens increased by 1.19 times in the temperature range of ?20 to 120 °C. The thermal decomposition temperature of the composites was influenced by the effect of the crystal field and size effect of CaCO₃.     

Properties of white birch (Betula papyrifera) outer bark particleboards with reinforcement of coarse wood particles in the core layer

? This study proposes substituting traditional raw materials in the surface layers of wood particle-boards with the water resistant white birch (Betula papyrifera) outer bark particles, which can help improve the dimensional stability of manufactured mixed particleboards, thereby alleviating shortages of raw material in a cost-efficient manner.

? Mixed particleboards were fabricated in the laboratory using untreated or alkali treated white birch outer bark particles as substitute material. These particles were resinated successively with three percentages of phenol-formaldehyde resin. Overall, the results of this study clearly demonstrate that the panels could be manufactured using up to 45% of the proposed substitute material and still maintain the required mechanical and physical properties.

? Alkali treatment was used to remove natural wax from bark particles surface which hinders resin adhesion. This treatment negatively affected mechanical and physical properties of finished panels and the variation of phenol-formaldehyde resin percentage in the bark particles significantly affected only their hardness.

? Panel with untreated bark particles in the surface layers, resinated with 5% phenol-formaldehyde resin was selected as the best with the help of a statistical analysis carried out in a factorial complete block design, especially from the dimensional stability criterion.

     

Wettability changes of wheat straw treated with chemicals and enzymes

A study was conducted to test wettability changes of the wheat straw treated with different methods for the preparation of wheat straw particle board. The wheat straws were separately sprayed with two chemicals (0.6% NaOH, 0.3% H2O2) and three enzymes (lipase, xylanase, cellulase). The contact angle between water and the surface of wheat straw was measured and the spreading-penetration parameters (K-values) were also calculated with wetting model. The surfaces of treated wheat straw and control sample were scanned by means of Micro-FTIR, and their peaks arrangements were analyzed. The surface morphologies of treated wheat straw and control sample were also observed by SEM. Chemical etching was found on the exterior surfaces of the straws treated separately with 0.6% NaOH and 0.3% H2O2; furthermore, the spreading-penetration parameters (K-values) of the distilled water on the exterior surfaces of the treated wheat straw along the grain were higher than that of control. The wettability of exterior surfaces of the wheat straws treated separately with lipase, xylanase and cellulose were improved after treating for seven days, and among the three enzymes treatments, the lipase treatment showed best result. The lipase treatment and NaOH treatment were determined as better methods for improving the wettability of wheat straw surfaces. However, in the economic aspect, NaOH treatment was more practical and easier in the pretreatment for the manufacture of straw particle board.     

Investigation of a new natural adhesive composed of citric acid and sucrose for particleboard

The development of a natural adhesive composed of materials derived from non-fossil resources is a very important issue. In this study, only citric acid and sucrose were used as adhesive materials for particleboard. A water solution in which citric acid and sucrose were dissolved was used as an adhesive, and the manufacture of particleboard with a target density of 0.8 g/cm³ was attempted under a press condition of 200 °C for 10 min. The optimum mixture ratio of citric acid and sucrose and the optimum resin content was 25–75 and 30 wt%, respectively. The modulus of rupture (MOR) and the modulus of elasticity in bending were 20.6 MPa and 4.6 GPa, respectively. The internal bond strength (IB) was 1.6 MPa, indicating that the adhesive had excellent bond strength. The thickness swelling (TS) after water immersion for 24 h at 20 °C was 11.9 %. The board did not decompose even under more severe accelerated treatments. This meant that the adhesion had good water resistance. The MOR, IB and TS of the board were comparable to or higher than the requirement of the 18 type of JIS A 5908 (2003). Consequently, there is a possibility that a mixture of citric acid and sucrose can be used as a natural adhesive for particleboard.     

卫浴用树脂浸渍单板重组材的尺寸稳定性

为满足卫浴装饰装修用木材的需求,以速生桦木为原料,开发出一种树脂浸渍单板重组材。通过分析浸渍三聚氰胺-甲醛(MF)树脂固体含量、浸渍方法、热压压力等因子对板材尺寸稳定性的影响,结果表明:当MF树脂固体含量45%、热压压力1.0MPa,采用辊压浸渍(压榨率50%～70%)时,板材的极限体积膨胀率为6.2%,低于水曲柳、栎木等实木试件,尺寸稳定性大大改善。