Hydroxymethylated resorcinol (HMR) priming agent for improved bondability of silicone modified wood glued with a polyvinyl acetate adhesive

A hydroxymethylated resorcinol (HMR) was used as a coupling agent to improve glueability of silicone (aminofunctional polydimethylsiloxane) modified pine sapwood (Pinus sylvestris) with polyvinyl acetate (PVAc). Priming with HMR did not significantly increase tensile shear strength of unmodified and silicone treated wood under dry conditions. Under wet conditions, tensile shear strength of the control specimens was increased by 37% and of the silicone modified specimens by 13%. Despite of higher shear strength under wet conditions, the primed silicone treated specimens displayed lower degree of wood failure than the unprimed treated specimens.     

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.     

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.     

Properties of laminated veneer lumber (LVL) made with low density hardwood species: effect of the pressure duration

Cross-linked polyvinyl acetate (PVAc) adhesive and thin veneers of three low density wood species, namely silver maple, yellow poplar and aspen, were used to produce LVL engineered wood products using different press durations. Density, water absorption, thickness swelling, flexural strength and surface hardness were evaluated. Internal bond strength, tensile shear and block shear strengths were tested in dry, accelerated (boiling and dry) and cyclic (wet and dry) conditions. LVL made using cross-linked polyvinyl acetate and silver maple with a platen temperature of 38 °C for 5 minutes exhibited the best properties. LVL of silver maple veneers showed improved properties as compared to yellow poplar and aspen. Silver maple can be used suitably in laminated veneer flooring.     

Effects of cold setting adhesives on properties of laminated veneer lumber from oil palm trunks in comparison with rubberwood

In this study, the properties of laminated veneer lumber (LVL) made from oil palm trunks (OPT) were evaluated in comparison with rubberwood using cold setting adhesives, namely, emulsion polymeric isocyanate (EPI) and polyvinyl acetate (PVAc). The evaluations were based on either dry or after cold water, hot water and cyclic pre-treatment. The density of the OPT LVL was slightly higher than that of solid OPT. Thickness swelling and water absorption of OPT LVL were greater than of rubberwood LVL. Pre-treatment increased the water absorption and thickness swelling. The OPT LVL bonded with EPI without toluene showed greater water absorption and thickness swelling than EPI with toluene. Pre-treatment significantly reduced the tensile strength of OPT LVL. The OPT LVL bonded with EPI without toluene showed higher tensile shear strength, but a greater reduction of tensile shear strength after pre-treatment, than the OPT LVL bonded with EPI and toluene. The PVAc adhesive had greater wettability than the EPI. The EPI without toluene showed a lower contact angle than the EPI with toluene. The loose side of the OPT veneer was found to have greater wettability than the tight side.     

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.     

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。     

人工林杉木胶合工艺优化研究

采用SAS全因子试验设计,研究了胶粘剂类型、涂胶量、单位压力、加压时间和胶合面纹理五个因子对人工林杉木木材胶合性能的影响,并对其胶合工艺进行了优化。研究结果表明:胶粘剂类型对杉木木材常态胶合剪切强度和木破率的影响不显著,但是老化处理后API和PF的胶合剪切强度和木破率比PVAc和UF的要高;在以API为胶粘剂时,涂胶量、单位压力、加压时间和胶合面纹理对杉木胶合剪切强度和木破率的影响显著,优化的胶合工艺为涂胶量250g/cm2,单位压力1.5 MPa,加压时间50 min和胶合面纹理为弦切面-弦切面。     

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.     

胶黏剂种类对人造板内结合强度检测结果的影响

使用聚乙酸乙烯酯乳液(PVAc)、单组份聚氨酯(PUR)和热熔胶(EVA)3种胶黏剂粘结金属卡头与试件,检测并分析它们对强化木地板和地板基材用纤维板内结合强度检测结果的影响。结果表明:使用PUR粘结时检测的内结合强度值比使用PVAc、EVA高,其中强化木地板内结合强度高出0.47MPa,地板基材用纤维板内结合强度高出约0.40MPa。     

胶黏剂种类对人造板内结合强度检测结果的影响

使用聚乙酸乙烯酯乳液（PVAc）、单组份聚氨酯（PUR）和热熔胶（EVA）3种胶黏剂粘结金属卡头与试件,检测并分析它们对强化木地板和地板基材用纤维板内结合强度检测结果的影响。结果表明：使用PUR粘结时检测的内结合强度值比使用PVAc、EVA高,其中强化木地板内结合强度高出0.47MPa,地板基材用纤维板内结合强度高出约0.40MPa。     

Bonding surface-modified Karri and Jarrah with resorcinol formaldehyde

A series of abrasive papers were used to sand machined regrowth karri (Eucalyptus diversicolor) and regrowth jarrah (E. marginata) wood surfaces. Shear test specimens were then prepared by gluing sanded wood blocks with resorcinol-formaldehyde and pressing them at 1500 kPa and 20°C for 7 hours. Wettability measurements on sanded wood surfaces and strength tests on shear test specimens were used to assess the ability of the sanding treatment to improve adhesive performance. The effect of sanding on wettability and shear strength varied according to the abrasiveness of the sanding treatment. Application of the coarsest abrasive (80 grit) significantly improved wettability and shear (adhesive) strength in both dry and wet conditions. A positive correlation between wettability and shear strength occurred only after sanding. SEM observations revealed different morphological structures of the glueline in sanded and non-sanded surfaces.     

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。     

Characterization of a formaldehyde-free cornstarch-tannin wood adhesive for interior plywood

This study investigated the physical properties (rheological and thermogravimetric analysis) of cornstarch-tannin adhesives and the mechanical properties (dry tensile strength and 3-point bending strength) of plywood made using cornstarch-tannin adhesives. This adhesive was evaluated for its utility in interior plywood manufacture. The optimum cure temperature and cure time of cornstarch-tannin adhesives were 170°C and 4?min, respectively. Plywood bonded with formaldehyde-free cornstarch-tannin adhesive exhibited excellent mechanical properties comparable to commercially available phenol-formaldehyde plywood adhesives. It was found that cornstarch-tannin panels which do not contain formaldehyde and with an emission equal to that of heated but unbound wood can be obtained by the use of hexamethylenetetramine (hexamine) as hardener. The work has indicated that an environmentally friendly wood adhesive can be prepared from a natural renewable resource (cornstarch and wattle tannin) for bonding interior-type plywood.     

The influence of compression failure on the bending, impact bending and tensile strength of spruce wood and the evaluation of non-destructive methods for early detection

Bending strength (MOR) and bending Young’s modulus (MOE) according to DIN 52186 and MOE calculated on the basis of eigenfrequency and sound velocity were tested on small clear wood specimens of Norway spruce wood with and without compression failure. One group of specimens was climatised in a normal climate of 20°C and 65% relative humidity, while the other group was stored for one month under water before testing. The MOR of specimens with compression failure decreased about 20% on average (normal climate and wet) compared with the specimens without compression failure. The MOE of the specimens with compression failure was reduced only minimally compared with the specimens without compression failure stored in a normal climate, but very distinct differences (more then 30%) were found under wet conditions. The MOE of the specimens with compression failure calculated on the basis of eigenfrequency and sound velocity were not reduced or only minimally compared with the specimens without compression failure. It is therefore not possible to detect compression failure and to determine reduction in MOR using eigenfrequency or sound velocity. In addition, impact bending (DIN 52189), tensile strength and tensile MOE (DIN 52188) were tested on small clear wood specimens of Norway spruce wood with and without compression failure. The specimens with compression failure revealed an average reduction in impact strength of about 40% and an average reduction in tensile strength of about 20% compared with the specimens without compression failure, whereas tensile MOE of the specimens with compression failure was not reduced compared with the specimens without compression failure. The detection of compression failure by computer tomography (CT) was tested on Norway spruce wood boards 10 cm in thickness, and detection by optical scanner was tested on planed Norway spruce wood boards. CT recognised large compression failures easily, whereas the scanner was not able to detect them.     

Quantitative determination of bound water diffusion in multilayer boards by means of neutron imaging

Diffusion processes into multilayered samples of Norway spruce (Picea abies [L.] Karst.) exposed to a differentiating climate (dry side/wet side) were determined and quantified by means of neutron imaging (NI). The experiments were carried out at the neutron imaging facility NEUTRA at the Paul Scherrer Institute (PSI) in Villigen (Switzerland). With NI the influence of different adhesives (polyvinyl acetate (PVAc), urea formaldehyde resin (UF), epoxy resin (EP), one-component polyurethane (1C PUR)) on the diffusion process could be determined by varying the layer number and the thickness of adhesive joints of the samples. Thereby, neutron transmission images were used to measure time dependent water profiles in the diffusion direction. Using Fick’s second law, diffusion coefficients for radial and tangential water transport in spruce wood and in the adhesive joints were calculated depending on moisture content (MC). It was found that the diffusion coefficients of the adhesives (1C PUR, EP at high MC) were up to three orders of magnitude lower than those of spruce wood. PVAc and UF had a smaller barrier effect compared to wood, which in contrast to 1C PUR and EP, clearly depends on the MC.     

Isocyanat-Verleimung von Spanplatten unter Berücksichtigung spezieller Holzargen

In laboratory particleboards whose surface and core layers were bonded with phenolic formaldehyde resin and isocyanate respectively, a certain influence can be noted of the use of specific wood species for core layers that consist exclusively of chips from those wood species. Of all investigated wood species (alder, poplar, spruce, pine, birch, beech and oak) alder showed maximum values with regard to dry and wet internal bond whereas minimum values were recorded for beech and oak. The very low wet internal bond values for beech and oak were particularly remarkable. Wool particles were produced from cut poplar particles in the laboratory and used for the core layer. The other wood species were mixed with these poplar wool particles and with cut pine particles at a ratio of 50:50. In most wood species the addition of poplar wool particles produced better wet internal strength values than were achieved with unmixed core layers. Poplar wool particles improve wet internal bond properties of beech and oak particleboards to a far greater extent than do cut pine particles.     

Evaluation of strength properties of parallel splint lumber (PSL) and its comparison with laminated veneer lumber (LVL), rubber wood and teak

Heavea brasiliensis ) and an exterior type of adhesive were evaluated in air-dry condition. Block shear tests were also carried out in wet and dry condition. Comparisons of these strength values were made with those of laminated veneer lumber (LVL), solid rubber wood and standard teak. The results show that PSL has slightly lower values of strength properties compared to teak, solid rubber wood and quite inferior ones to those of LVL. On the basis of the data obtained in the present study, PSL made from rubber wood can be utilised as a structural material for different purposes like door and window frames, rigs and trusses.     

Environmental effects on the bond at the interface between FRP and wood

The advantages of fiber reinforced polymer (FRP), such as high specific strength, resistance against corrosion and formability, have made it a more acceptable alternative to conventional materials regarding repairing and retrofitting of structures. Although investigations in recent years have proved the concern of civil engineers about the environmental effects on the bond between FRP and concrete or masonry (especially moisture and temperature), only few researches have been reported on FRP-wood interfaces. This research investigated the effect of five different environments on the bond at the interface between FRP and wood. A series of pull-out tests were performed on 375 wood specimens bonded with aramid, carbon and glass fibers (wet lay-up) and one type of epoxy resin. Then, these samples were immersed in chemical solutions with pH of 2.5, 7, 10 and 12.5 and substitute sea water for 2, 4, 6, 8, 10 and 13 weeks to estimate bond strength reduction. The effect of dry heat was also investigated. The results of such experimental tests illustrated that an acidic solution had the most effect on the bond between carbon-FRP and wood by 57% reduction. Sea water and fresh water had almost the same effect on the specimens bonded with glass and aramid–FRP (40% reduction), and they had the least influence on the bond between carbon-FRP and wood. Further, alkaline solutions had the most effect on the specimens bonded with glass-FRP. In addition, dry heat did not affect the bond between FRP and wood considerably.