六种人工林木材胶合性能初步研究

初步研究了杉木、杨树、巨桉、尾巨桉、柠檬桉和窿缘桉等六种人工林木材的胶合性能,结果表明:胶合剪切强度沿杉木、杨树、巨桉、尾巨桉、柠檬桉和窿缘桉顺序增大;六种木材胶合性能差异显著,其中杉木、杨树、巨桉和尾巨桉胶合性能较好,表现为胶合剪切强度能达到标准要求、且木破率高;柠檬桉和窿缘桉木破率低,难于胶合,胶合性能有待改进;胶粘剂类型影响木材胶合性能,其中API和PF剪切强度和木破率平均值高于PVAc和UF;热压胶合的PF和UF的离散性比冷压胶合的API和PVAc要差。     

柞木弦／径切面胶合强度的试验研究

对柞木木材自身弦／径面强度及其水性高分子异氰酸酯(API)胶粘剂胶合试件弦／径面胶接强度进行了研究。结果表明:柞木木材API胶粘剂弦／径面胶合试件常态压缩剪切强度存在着差异;柞木径切面API胶合试件的常态压缩剪切强度比弦切面胶合试件的常态压缩剪切强度高;径切面API胶合试件的常态压缩剪切强度是弦切面的1.22倍;而柞木弦、径面API胶合试件的反复煮沸压缩剪切强度没有显著性的差别。柞木木材本身弦／径面顺纹抗剪强度试验结果表明:柞木木材径向的顺纹抗剪强度为14.41MPa,柞木木材弦向的顺纹抗剪强度为14.97MPa,尽管弦径向间差别不大,但经t-检验证明:柞木的弦／径向间顺纹抗剪强度有显著性的差别,柞木的径向顺纹抗剪强度比弦向顺纹抗剪强度小。     

基材对API胶黏剂粘接强度的影响

对水性高分子聚合物为主剂、异氰酸酯为固化剂的API胶合体系进行了研究,主要考察了被粘接基材的类型、试材的弦、径向以及偶联剂处理基材对API粘接强度的影响。实验结果表明:用于胶合试材的种类和试材的密度、试材的纹理走向对胶合强度均有影响,偶联剂HMR对改善胶的耐热、耐水性能,提高胶合面的木材破坏率效果显著。     

马尾松单板胶合工艺优化研究

涂胶量和热压工艺对单板类人造板性能影响很大。本文以马尾松单板和酚醛树脂胶粘剂为原料,采用单因素试验探讨了涂胶量对板材胶合性能的影响;采用全面试验探讨了热压参数(热压压力、热压温度和时间)对板材性能的影响。试验结果表明:随着涂胶量的增大,板材胶合强度呈现先增后减的变化,采用250g/m2的涂胶量是较优选择;热压工艺参数对胶合板的胶合强度有较大影响,综合考虑,热压压力为1.5MPa、温度为150℃、热压时间为1.2min/mm的条件下,马尾松胶合板的各项指标能够达到较优。     

桉木芯集成材饰面工艺的研究

以桉木芯集成材为基材,以乌金木和科技木薄木为饰面材料,针对贴面后易产生的胶合质量问题进行了研究。结果表明:涂胶量对透胶的影响最大,热压温度和涂胶量对浸渍剥离均有较大影响,热压温度对表面胶合强度的影响最大。本试验范围内,较佳贴面工艺为涂胶量90 g/m~2,单位压力0.6 MPa,热压温度100℃,热压时间180 s。     

单板层积材侧面贴面装饰工艺研究

以桉木单板层积材侧面为基材,以黑胡桃薄木和装饰纸作为饰面材料,考察了涂胶量、热压时间、热压压力和热压温度等工艺参数对透胶、浸渍剥离、表面胶合强度的影响。结果表明：以黑胡桃薄木和装饰纸为饰面材料时,涂胶量对透胶影响最大,热压温度对浸渍剥离与表面胶合强度影响最大。以黑胡桃薄木与装饰纸为饰面材料时的最佳工艺分别为：涂胶量100g/m^2与110 g/m^2,单位压力0.8 MPa,热压温度100℃,热压时间240 s与180 s。     

脲醛树脂浸渍改性杨木胶合及涂饰性能

研究脲醛树脂浸渍改性杨木的胶合和涂饰性能。结果表明:本试验范围内,胶黏剂种类对木材胶合性能有重要的影响,三种胶黏剂对改性材的胶合剪切强度均大于素材,并且改性材木破率低于素材;脲醛树脂胶合改性材的剪切强度、木破率均较高。涂料种类对浸渍改性杨木涂饰性能有影响,硝基漆和水性漆涂饰的改性材和素材的漆膜附着力均为优等品,而聚氨酯漆漆膜附着力不合格,改性前后杨木的漆膜附着力基本没有改变。     

尾巨桉材Ⅰ类胶合板制造技术的研究

采用正交试验法研究单板涂胶量、热压温度、热压时间3个因子对尾巨桉材Ⅰ类胶合板性能的影响,得出了较优的工艺参数.结果表明,单板涂胶量、热压温度、热压时间对尾巨桉胶合板的胶合强度影响显著,其中热压时间影响最大,热压温度其次,单板涂胶量最小;较优的生产工艺组合是单板涂胶量320g/m2、热压时间1.2min/mm、热压温度135℃.     

竹集成材组坯结构的优化

对比分析了水、脲醛树脂胶黏剂和酚醛树脂胶黏剂在毛竹竹片的竹青侧与竹黄侧弦切面的接触角,并测试了不同胶合面间的胶合强度,以优化竹集成材的结构。试验结果表明,竹青侧弦切面的润湿性能比竹黄侧弦切面差;两竹青侧弦切面间的胶合强度最差,而两竹黄侧弦切面间的胶合强度最好。根据胶合强度的差异、材料弯曲力学原理、竹材本身的组织结构差异,建议竹集成材的组坯采用对称原则、偶数层原则,或采用工字结构板材,以提高竹集成材的物理力学性能。     

弱碱性速生大青杨胶合板胶合工艺的研究

大青杨是弱碱性速生材种(芯材PH=8.5—9.0).为了扩大胶合板用材树种,我们利用实验室仪器和设备,通过大量实验,在单板含水率、涂胶量、固化剂种类及其用量、热压温度和压力等因素保持相对不变的前提下,研究了热压时间、填料用量和陈化时间对合板胶合强度的影响探讨了合板胶合的工艺条件.     

Hydroxymethylated resorcinol (HMR) priming agent for improved bondability of wax-treated wood

The effects of hydroxymethylated resorcinol (HMR) on the tensile shear strength of wood joints treated with montan ester wax were studied with polyvinyl acetate (PVAc) and melamine formaldehyde (MF) adhesives. Untreated specimens which were bonded with MF and PVAc had similar bond strength properties under dry conditions, but MF bonded specimens’ tensile shear strength values were higher than that of PVAc glued specimens under wet conditions. With both adhesives tested, dry tensile shear strengths of wax-treated specimens were in a comparable range to those of untreated wood, while under wet conditions the strength values of wax-treated specimens were significantly lower than those of the controls. HMR priming increased the shear strength of PVAc bonded specimens under wet conditions and of MF-bonded specimens under dry and wet conditions. The effect on MF-bonded specimens, however, was much more pronounced under wet conditions.     

PVC/木粉复合材料粘接用胶黏剂的选择

按照GB/T 7124—2008检测各种胶黏剂粘接的PVC/木粉复合材料胶合试件的拉伸剪切强度,通过对比筛选出粘接效果较好的胶黏剂。试验结果表明：在试验所选择的胶黏剂中环氧树脂胶黏剂、J-39丙烯酸酯胶黏剂以及乳白胶粘接强度相对较高。     

PVC/木粉复合材料粘接用胶黏剂的选择

按照GB/T 7124—2008检测各种胶黏剂粘接的PVC/木粉复合材料胶合试件的拉伸剪切强度,通过对比筛选出粘接效果较好的胶黏剂。试验结果表明:在试验所选择的胶黏剂中环氧树脂胶黏剂、J-39丙烯酸酯胶黏剂以及乳白胶粘接强度相对较高。     

Bonding performance of heat treated wood with structural adhesives

Bonding of untreated, intermediate (hydro-thermolysed) and heat treated wood with melamine-urea-formaldehyde (MUF), phenol-resorcinol-formaldehyde (PRF) and polyurethane (PUR) adhesives was studied. An industrial heat treatment process (Plato ^®) was used, which included two separate heat treatment stages and a drying stage in-between. Laminated beams having four lamellas were prepared from untreated and treated timber for mechanical testing of the bond lines. The results of the tests showed that heat treatment affected the shear strength and the delamination of the laminated wood depending on the adhesive system used for bonding. The PUR and MUF adhesives performed in a rather similar way, and better than the PRF adhesive. The shear strength of laminated wood bonded with the waterborne MUF and PRF adhesives decreased for the specimens made of hydro-thermolysed timber and decreased further for the specimens made of fully heat treated timber. The difference in adhesive bond shear strength between untreated, intermediate and fully treated wood was less obvious in the case of the PUR adhesive. Delamination of the PRF bond line decreased drastically for all the specimens made of heat treated timber.     

PVC/木粉复合材料胶接件拉伸剪切强度的研究

参照国家标准GB/T 7124-2008《胶粘剂拉伸剪切强度的测定（刚性材料对刚性材料）》检测PVC/木粉复合材料胶合试件的拉伸剪切强度,发现：PVC/木粉复合材料胶合试件的断裂均发生在粘接区域外的复合材料本身,因而无法比较胶黏剂的粘接强度。为了能比较胶黏剂胶接接头的粘接强度,实验中将GB/T 7124-2008中规定的试件的厚度从1.6 mm加大至4mm。实验结果表明：采用环氧树脂粘接的PVC/木粉复合材料的拉伸剪切强度值高于用J-39丙烯酸酯胶黏剂粘接的复合材料的拉伸剪切强度。     

Bonding of densified beech wood using adhesives based on thermally modified soy proteins

The bondability/glueability of aged and sanded thermo-hydro-mechanically (THM) densified beech wood (Fagus sylvatica L.) was tested and compared with undensified sanded beech wood as a control. THM and control specimens were bonded with five different soy protein isolate (SPI) based adhesives. Commercial SPI powder was thermally modified in the vacuum chamber at 50 or 100?°C and pH adjusted (to pH 10.0) dispersions in water prepared at 24, 50 or 90?°C. Wettability was determined with measuring the sessile drop contact angles of water. Effective penetrations (EPs) and tensile shear strengths of THM and control specimens were determined. THM and control wood had similar wettability. Although THM wood had lower moisture content than control wood, it absorbed the water more slowly than control wood. THM specimens showed lower EPs than control specimens when comparing individual adhesives due to increased density of THM wood. Adhesives prepared with SPI thermally modified at 50?°C showed statistically significantly lower tensile shear strength of bonded THM specimens than that of bonded control specimens. THM densification had no significant effect on the bonding strengths of adhesives prepared with non-modified SPI and SPI thermally modified at 100?°C.     

Failure mechanisms in wood joints bonded with urea-formaldehyde adhesives

Wood joints bonded with urea-formaldehyde (UF) are weakened by cyclic swelling and shrinking. To study the failure mechanisms in UF-bonded joints, specimens were bonded with unmodified, modified (amine), or phenol formaldehyde adhesive and subjected to accelerated aging. Modification of the adhesive properties increased the cleavage fracture toughness and shear strength of bonded joints and improved the resistance of joints to cyclic swell-shrink treatment and accelerated moist-heat aging. Joints bonded with some modified urea-formaldehyde adhesives were as resistant to these treatments as joints bonded with phenol formaldehyde. Physical and mechanical origins of the improved adhesive performance were determined by microscopic analysis. Cure-shrinkage stresses precracked unmodified adhesive layers and damaged the wood interphase. The damaged interphase was especially susceptible to the effects of cyclic swelling and shrinking stresses. Certain modifiers reduced or eliminated cure-shrinkage cracking and damage to the wood. Moist-heat aging caused molecular scission in the bulk unmodified adhesive layer as revealed by the onset of shear cracking in the adhesive layer and erosion of exposed surfaces. Certain modifiers reduced or eliminated molecular scission and erosion responsible for adhesive weakening in moist-heat aging. We conclude that incorporating flexible amines in the adhesive structure improves the durability and stability of UF-bonded joints.     

Thermal stability of glued wood joints measured by shear tests

The thermal stability of glued wood joints is an important criterion to determine the suitability of adhesives in the field of engineered wood. During their product life, glued wood joints can be exposed to high temperatures in various ways (direct exposure to the sun, fire, etc.). Thereby the cohesiveness of the adhesive must not degrade. This raises the question of how the strength of bonding changes under thermal load. The current investigation covers the influence of temperature (T=20 to 220°C) on the shear strength of glued wood joints. Different adhesive systems were investigated. With increasing temperature, the shear strength of solid wood and also of glued wood joints decreased. There were big differences in thermal stability and failure behaviour between the adhesive systems as well as within the polyurethane group. The thermal stability of one-component polyurethane systems can be greatly varied by modifying their chemical structure. Well adapted one-component polyurethane adhesives reach a strength similar to that of phenol resorcinol resin.     

Structural bonding of ash (Fraxinus excelsior L.): resistance to delamination and performance in shearing tests

The utilization of ash (Fraxinus excelsior L.) allows for a significant enhancement of the load-bearing capacity in structural laminated products. However, such applications fundamentally require high-strength and durable bonds between lamellas and in finger joints. Therefore, the aim of the present survey was to evaluate ash bondings in terms of resistance to delamination (EN 302-2) and shear performance (EN 392). Investigations were performed with five adhesives: phenol-resorcinol-formaldehyde (PRF), melamine-urea-formaldehyde (MUF-1, MUF-2), polyurethane (PUR), emulsion polymer isocyanate (EPI) and varying closed assembly times as key bonding parameter. For all tested adhesives and closed assembly times, the shear test showed high wood failure percentages and bond strength values that compare to solid ash. In contrast, for resistance to delamination, significant differences were found between the adhesives as well as between closed assembly times, with improving resistance to delamination for increasing closed assembly times. The best performance was determined for the PRF-adhesive and long closed assembly times. However, standard requirements for resistance to delamination could not be met by any of the adhesives. The resistance to delamination showed no correlation with the shear performance for any of the adhesives. Microscopic examination of the bonded joints revealed that both the penetration behavior of the adhesives and glueline thicknesses clearly correlated with the closed assembly time.     

Bondline shear strength and wood failure of European and tropical hardwood glulams

The study reports on block shear investigations with bondlines of face-glued laminations and matched solid wood specimens from hardwood glulam (GLT) beams produced industrially from eight technically and stand volume-wise important species. The European hardwoods comprised oak, beech, sweet chestnut and ash and the tropical species were teak, keruing, melangangai and light red meranti. The adhesives were phenol-resorcinol and melamine-urea. When combining all species in one sample, a rather strong linear relationship of bond and wood shear strength was observed. The ratio of bond vs. wood shear strength was for all species on the mean value level?≥?0.9, and likewise (with one exception) for the respective strengths’ 5%-quantiles. Consistent with literature, the test results showed no significant correlations between bond shear strength and density, wood shear strength and wood failure percentage of individual species, respectively. The investigations render the methodological basics of some international standards on bond quality verification as being inappropriate. New, empirically validated hardwood GLT bond requirements are proposed for discussion and implementation at the CEN and ISO levels. The strength ratio specifications reflect respective ANSI provisions, yet the reference quantity wood shear strength is now determined in an unbiased manner from matched GLT specimens. The wood failure verification proposal is based on the 10%-quantile and mean level for initial type testing and factory production control. The requirements further account for the pronounced difference observed in scatter of wood failure between European and tropical species.