The potential of phenol–formaldehyde as plasticizing agent for moulding applications of wood veneer: two-dimensional and three-dimensional moulding

Two phenol–formaldehyde resols, namely a low and a medium molecular weight phenol–formaldehyde, were investigated for their applicability as plasticizers in moulding of European beech veneer (Fagus sylvatica L.). Therefore, beech veneers specimens were impregnated with both phenol–formaldehyde resol types in various concentrations. Subsequently, two-dimensional mouldability of the veneer was tested in a three-point-bending test along and perpendicular to the grain. Additionally, three-dimensional moulding of the phenol–formaldehyde impregnated veneer was tested throughout a modified Erichsen cupping test, where the veneer is pressed through a circular shaped coining die. The obtained results indicate a significantly improved mouldability of the treated beech veneers compared to untreated, water-saturated control specimens. Even at low phenol–formaldehyde concentrations plasticizing effects were detected in longitudinal direction and perpendicular to the grain. These findings are substantiated by results from three-dimensional moulding. Furthermore, the low molecular weight phenol–formaldehyde treated veneers displayed a higher mouldability than medium molecular weight phenol–formaldehyde specimens at similar phenol–formaldehyde concentration.     

Evaluation of white rot decay in phenol-formaldehyde resin treated European beech (Fagus sylvatica L.) LVL by drilling resistance measurements

Improving the properties of laminated veneer lumber (LVL) through wood modification expands its usage as building material, especially for outdoor applications. The outdoor performance of LVL products needs to be tested against different biotic agents, and methods are needed for testing and evaluating their effect on the structural integrity of LVL. In this study, drilling resistance (DR) measurements were used to quantify the effect of fungal decay in phenol-formaldehyde (PF) resin treated European beech (Fagus sylvatica L.) LVL caused by white rot fungi. Material specific peculiarities and their effect on the evaluation method were studied such as the effect of drill bit blunting, moisture content (MC), drilling direction and PF resin content on the DR of PF-modified LVL. The drilling direction in relation to veneer and glue layers had a significant effect on DR and feeding resistance (FR). The PF resin treatment increased the DR. Feeding resistance was found more sensitive to the blunting of the drill bit than DR. The effect of MC on DR and FR was found to be insignificant. The effect of PF resin content on the prediction of mass loss (ML) by DR became prominent only for ML by white rot decay below 10 %. Correlations between DR, ML due to fungal decay and weight percent gain were established and described with a two-factor regression model. The drill bit feed rate of 0.5 m min^?1 and the rotational frequency of 3500 min^?1 as well as the transversal drilling in relation to the veneer (glue) layers were recommended for the assessment of beech LVL treated with PF resin. The DR measurements showed high potential as a fast standard evaluation method for decay and strength loss of LVL products.

     

杨木单板层积材单板斜接质量胶接工艺探讨

单板纵向接长是单板层积材(LVL)生产的核心环节,单板斜接质量的好坏直接影响生产效率、产品外观质量和内在强度。本文探讨了非结构用杨木LVL产品中的单板斜接生产工艺改进方法,由使用酚醛树脂胶改为三聚氰胺改性脲醛树脂胶,并验证了其可行性。     

Properties of laboratory made yellow poplar (Liriodendron tulipifera) laminated veneer lumber: effect of the adhesives

Four different commercial resin formulations namely cross-linked polyvinyl acetate (XPVAc), melamine urea formaldehyde (MUF), urea formaldehyde (UF) and melamine formaldehyde (MF) were used to produce laminated veneer lumber (LVL) from yellow poplar veneers in the laboratory. Physical and mechanical properties were evaluated using ASTM (D 1037, D 906, D 5456) standards and compared. Internal bond, tensile shear and block shear strengths of specimens subjected to accelerated (boiled water) and cyclic (repeated cold water) conditions were also determined. Strength properties of yellow poplar LVL were improved compared with the solid wood. The properties of XPVAc bonded LVL were superior or comparable to the thermosetting adhesives. This study clearly indicated that cross-linked PVAc can be used to manufacture LVL with acceptable properties.     

Paper-based laminates produced with kraft lignin-rich phenol–formaldehyde resoles meet requirements for outdoor usage

Suitability of lignin–phenol–formaldehyde (LPF) resoles was investigated for manufacturing paper-based high-pressure laminates. As lignin source, pine kraft lignin and spruce sodium lignosulfonate were compared, substituting 40 wt% of phenol by lignin in each case. The synthesized resins were characterized for their viscosity development, solid content, pH, free formaldehyde as well as free phenol content and B-time. Paper-based high-pressure laminates were manufactured using the two different resins. The laminates were exposed to different test climates and were compared for boiling water resistance, thickness swelling, bending properties and impact energy. The results indicate that pine kraft lignin performs superior to spruce sodium lignosulfonate for utilization in paper based laminates for outdoor usage due to a lower affinity of the pine kraft LPF laminates to water.     

Effect of laminated structure design on the mechanical properties of bamboo-wood hybrid laminated veneer lumber

The effects of veneer orientation and loading direction on the mechanical properties of bamboo-bundle/poplar veneer laminated veneer lumber (BWLVL) were investigated by a statistical analysis method. Eight types of laminated structure were designed for the BWLVL aiming to explore the feasibility of manufacturing high-performance bamboo-based composites. A specific type of bamboo species named Cizhu bamboo (Neosinocalamus affinis) with a thickness of 6 mm and diameter of 65 mm was used. The wood veneers were from fast-growing poplar tree (Populus ussuriensis Kom.) in China. The bamboo bundles were obtained by a mechanical process. They were then formed into uniform veneers using a one-piece veneer technology. Bamboo bundle and poplar veneer were immersed in water-soluble phenol formaldehyde (PF) resin with low molecular weight for 7 min and dried to MC of 8–12 % under the ambient environment. All specimens were prepared through hand lay-up using compressing molding method. The density and mechanical properties including modulus of elasticity (MOE), modulus of rupture (MOR), and shearing strength (SS) of samples were characterized under loading parallel and perpendicular to the glue line. The results indicated that as the contribution of bamboo bundle increased in laminated structure, especially laminated on the surface layers, the MOE, MOR and SS increased. A lay-up BBPBPBB (B-bamboo, P-poplar) had the highest properties due to the cooperation of bamboo bundle and poplar veneer. A higher value of MOE and MOR was found for the perpendicular loading test than that for the parallel test, while a slightly higher SS was observed parallel to the glue line compared with perpendicular loading. Any lay-up within the homogeneous group can be used to replace others for obtaining the same mechanical properties in applications. These findings suggested that the laminated structure with high stiffness laid-up on the surface layers could improve the performance of natural fiber reinforced composites.     

Curing behavior and bonding strength of two-component fast-setting adhesives prepared with phenol-liquefied <Emphasis Type="Italic">Cryptomeria japonica</Emphasis> wood

Honeymoon adhesive is a special adhesive system that contains two components which are applied onto two substrates separately for glulam manufacturing to provide a fast-setting capability. It has been confirmed that phenol-liquefied wood can be used as a raw material for preparing phenolic resins. In this study, liquefied wood (LW) was obtained by liquefying Cryptomeria japonica wood in phenol with sulfuric acid as a catalyst. Resorcinol–formaldehyde resin (RF), phenol-resorcinol–formaldehyde resins (PRF), LW–PF and LW–PRF (synthesized using LW as a raw material), and RF/LW and RF/LW–PF (blended RF with LW and LW–PF) were prepared. The properties such as non-volatile content, pH, viscosity gelation time and DSC curing behavior of these resins were measured. The results show all resins can be cured at room temperature when paraformaldehyde is added as a hardener, except for the LW–PF. The honeymoon adhesive was prepared by using RF and PRF that contains 10% paraformaldehyde as the A-component and LW–PRF, RF/LW and RF/LW–PF without paraformaldehyde as the B-component. After mixing the A-component and B-component, the gelation time of RF and PRF can be shortened. The glued lumber was prepared by separately applying the A-component and B-component on the surface of two wood strips and combining them. The result shows using RF/LW–PF as the B-component has faster bonding strength development than others. When PRF and RF are used as the A-component, they have a bonding strength of over 5.4 MPa, the requirement of CNS 11031 standard for the glued lumber of C. japonica, at pressing times of 2 and 4 h, respectively.     

Enhanced fungal resistance of Scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) sapwood by treatment with methyltrimethoxysilane and benzalkoniumchloride

This paper presents possibilities for increasing the decay and mould resistance of Scots pine (Pinus sylvestris L.) sapwood by treatment: (1) in one step with mixtures of aqueous solutions of methyltrimethoxysilane (0, 5, 10, 20 or 30 % MTMS) and benzalkoniumchloride (0, 0.5, 1, 2 or 3 % BAC), and (2) in two steps, first with BAC and then with MTMS. Prior to fungal resistance tests, the treated and reference specimens were not or were subjected to artificial ageing in distilled water and in Xenotest, respectively. Insufficient anti-decay efficiency of MTMS against the brown-rot fungus Coniophora puteana and the white-rot fungus Trametes versicolor was improved in the presence of BAC, usually more apparent if this fungicide was used first and in higher concentrations. After both artificial ageing modes, the decay resistance of treated pine specimens decreased approximately 1.2–1.8 times. The none anti-mould efficiency of MTMS improved in the presence of BAC—significantly against the mould Penicillium brevicompactum but only minimally against the mould Aspergillus niger.     

Surface treatment for preventing decay and termite attack in wood using didecyl dimethyl ammonium tetrafluoroborate (DBF) incorporated with acryl-silicon type resin

Surface treatment of wood was carried out using acryl-silicon type resin including didecyl dimethyl ammonium tetrafluoroborate (DBF), boron-containing quaternary ammonia compound. Surface-treated wood specimens were exposed laboratory decay resistance tests after completing a 10-cyle severe weathering process. In laboratory decay resistance tests, one brown-rot decay fungus, Fomitopsis palustris and one white-rot decay fungus, Trametes versicolor were used. The specimens were also subjected to laboratory termite resistance tests using subterranean termites, Coptotermes formosanus. Wood specimens treated with 2% DBF and resin containing preservative solution showed improved decay and termite resistance suggesting that the preservative solution at 2% DBF concentration provides lasting protection against wood degradation owing to the amount of DBF remaining in the wood after severe weathering process. However field tests are needed to determine the performance of surface-treated wood with DBF and the acryl-silicon type resin in more realistic conditions.     

Modification of beech veneers with N-methylol-melamine compounds for the production of plywood

Rotary cut beech (Fagus sylvatica L.) veneers were treated with two formulations based on N-methylol-melamine (NMM): (1) NMM solution (NMM-1, 10% solid content), (2) fatty acid modified NMM dispersions containing paraffin (with an aluminium salt as catalyst, mNMM-2, 5% solid content). Five treated veneers were bonded with phenol formaldehyde (PF) adhesive to produce plywood in two different processes. The plywood treated with NMM-1 displayed increased shear strength in comparison to the controls, whereas the treatments with mNMM-2 diminished the shear strength of the plywood to different extents. Treatment with NMM-1 also enhanced other mechanical properties of the plywood as compared to water-treated control plywood such as Brinell hardness, modulus of elasticity and bending strength. The plywood treated with mNMM-2 showed only slight changes of these mechanical properties compared to the control plywood. The plywood specimens were subjected to cyclic water submersion and oven-drying. The treatment with mNMM-2 caused greater reduction in water uptake and thickness swelling than NMM-1; the degree of delamination depended on the process. The plywood treated with NMM-1 exhibited lower equilibrium moisture content than that treated with mNMM-2. The formaldehyde emission of NMM-1-treated plywood was much higher than that of the control and the mNMM-2-treated plywood.     

Production and characterization of particleboards from cork-rich <Emphasis Type="Italic">Quercus cerris</Emphasis> bark

Single-layered particleboards were produced from granulated Quercus cerris bark containing cork and phloem granules using standard hot-press equipment and phenol–formaldehyde resin. The experimental boards were tested for thickness swelling, mechanical strength and thermal properties. Scanning electron microscopy observations were carried out to analyze the panel structure. The results showed that Q. cerris bark particleboards had low thickness swelling in water, high resistance to thermal degradation and high calorific values but their mechanical strength was below that of commercial wood particleboards. The produced Q. cerris bark particleboards were adequate for exterior applications where mechanical strength is not the key factor. Potential for process and feedstock optimization was acknowledged.     

两种秸秆表面润湿性研究

研究测定了异氰酸酯、脲醛树脂和酚醛树脂胶粘剂对高粱秆与玉米秆表面的接触角,并通过测量不同表面张力的液体对秸秆表面的接触角,推算出秸杆表面的自由能.结果表明:秸秆的表面自由能比木材要低得多,属于低能表面固体.     

脲醛树脂废胶液制造胶合板工艺及性能研究

研究将脲醛树脂废胶液与水混合、中和处理、异味处理、磨浆、过滤得到混合浆液,将混合浆液按一定比例添加至酚醛树脂中,用于Ⅰ类胶合板及竹木复合集装箱底板用胶合板生产。研究结果显示,混合浆液添加比例8%和15%条件下,7层胶合板和21层竹木复合集装箱底板用胶合板胶合强度、浸渍剥离性能均满足Ⅰ类胶合板指标要求;混合浆液添加比例为12%~18%的酚醛树脂可用于竹木复合集装箱底板用胶合板生产,其各项性能高于国家标准要求;同时不改变胶合板的生产工艺,减少了危险固体废物的产生,实现脲醛树脂废胶液的资源化再利用。     

Adhesive bonding of beech wood modified with a phenol formaldehyde compound

Untreated (controls) and phenol–formaldehyde (PF)-modified beech wood (10 and 25?% solid content) were glued with phenol resorcinol formaldehyde (PRF) and polyvinyl acetate (PVAc). Shear strength of PRF-bonded specimens was higher than that of PVAc-bonded ones under dry and wet conditions irrespective of the pre-treatment. Under dry conditions, only PVAc-bonded specimens exhibited reduction in shear strength due to PF-modification with 25?% PF concentration as compared to the controls. PF treated wood provided inferior bonding under wet conditions with the exception of 25?% PF concentration specimens glued with PRF adhesive. Modification with PF resulted in a decrease of adhesive penetration into the porous network of interconnected cells, especially at 25?% PF concentration.     

Feasibility study of utilization of commercially available polyurethane resins to develop non-biocidal wood preservation treatments

Evaluation of commercially available polyurethane resins used up to now for coating applications to develop non-biocidal wood preservation treatments has been conducted. A simple method of vacuum impregnation of these resins into beech wood (Fagus sylvatica L.) and pine wood (Pinus sylvestris L.) samples followed by varied curing processes at ambient temperature, 103, and 200 °C has been performed. Based on the analysis of weight percent gain before and after leaching, treatment resistance to leaching, anti-swelling efficiency, wettability and decay durability measured for treated and untreated blocks after leaching with the white-rot fungus Coriolus versicolor for both wood species and the brown-rot fungi Poria placenta and Gloeophyllum trabeum for pine wood, it can be concluded that such treatment can be considered as potential valuable non-biocidal treatments.     

竹大片刨花板的防霉处理及其效果

对竹大片刨花板（BWB）作防青霉处理的试验结果表明：烷基铵类化合物（AAC）防霉剂的抗霉性大于硼酸,且药剂浓度越大则抗霉性越好;防霉剂对青霉菌的抑制效力随时间的延长而逐渐下降;无论酚醛树脂（PF）还是脲醛树脂（UF）对青霉菌基本无抑制作用;AAC表面处理和内部处理赋予竹大片刨花板的抗霉能力基本相同;烷基铵类防霉剂对PF-BWB的力学性能影响不大,但会导致UF-BWB力学性能的大幅下降。     

Experimental investigation of jet drying of birch and spruce veneers and modelling with a simplified approach

The paper presents experimental results of jet drying tests of birch ( Betula pendula) and spruce ( Picea abies) veneers at temperatures of 140°C and 190°C. Results include drying rates for 1.5 mm thick birch veneers as well as 1.5 mm and 2.6 mm thick spruce veneers of both heartwood and sapwood. Based on the test results, material parameter values for a simplified drying model are assessed. The model is based on the use of an effective diffusion coefficient and an effective surface emission coefficient, which values are calibrated to fit to the experimental results. It is observed, that separate model parameter sets are needed for the two different species but also for occurrence of heartwood or sapwood (spruce) and different thickness values of veneers.     

Inhibited wood degradation of cement-coated beech Laminated Veneer Lumber (LVL) for temporary in-ground applications

This paper investigates the long-term tensile properties of laminated veneer lumber (LVL) beech sections coated with cement and exposed to fungal decay. A set of LVL coupon (dog-bone) samples was stored in compost, tested in tension after 6 and 12 months and compared to reference samples stored at 20 °C and 65% relative humidity. Results showed that after 26 weeks of compost exposure, a fungus of the Ascomycota genus was identified in cement-coated samples using a molecular biology polymerase chain reaction (PCR) technique, which analyses the internal transcribed spacer (ITS) region of the ribosomal DNA. However, no visual deterioration was noticed. Still in cement-covered samples and after 12 months of exposure, a common white rot fungus was determined by DNA chip technology, but no fungal wood decay was visible in areas where the applied coating had a thickness of at least 5 mm. Decay in uncoated LVL samples was significant with the samples having an average residual strength equal to 7%. This compares to the tensile strength of coated samples, which only decreased by 65% relative to the reference samples. Strength and stiffness of coated samples did not differ significantly between 6 and 12 months of exposure. Preliminary investigations tend to show that the strength reduction in cement-coated samples is due to an alkaline degradation of the wood. The observed influence of the coating thickness on the visual fungal decay can probably be ascribed to the protection mechanism due to a physical fungal barrier with a high pH.     

制浆黑液在酚醛树脂胶黏剂中的应用

制浆黑液中的降解木质素含有酚羟基结构,可以替代部分苯酚制备酚醛树脂.以NaOH为催化剂,采用二次缩聚法制取酚醛树脂胶黏剂.实验表明,当黑液添加量为15%时,胶黏剂的黏度比空白实验增加1倍,游离甲醛含量降低了27%,胶合强度提高了13.2%.红外光谱分析表明,黑液中的木质素与游离甲醛反应生成有羟甲基的物质,该物质能与酚醛树脂胶粘剂中的物质发生反应,从而既降低了甲醛含量又提高了胶黏剂的胶合强度.     

酚醛树脂桉木单板层积材生产工艺研究

探讨利用酚醛树脂胶黏剂压制桉木单板层积材的工艺,分析了热压温度、热压时间和面粉添加量对桉木单板层积材力学性能的影响。研究表明：面粉添加量对桉木单板层积材的静曲强度和弹性模量有显著影响,而热压温度和热压时间的影响则不显著。就产品力学强度而言,较佳的工艺条件为：热压温度135℃,热压时间1.2 min/mm,面粉添加量0。验证试验证明,在实际生产中,综合生产成本及产品性能等多方面考虑,添加15%的面粉是可行的。