Hybrid silane-crosslinking polymers: a potential alternative to polyurethane wood adhesives? A preliminary investigation by TMA
In the last years, the research on wood adhesives has focused on matching technical performance with low health and environmental impacts. This study presents the first development of a new adhesive technology based on hybrid silane-crosslinking polymers that can combine both silicone’s and polyurethane’s adhesive properties. The advantage of hybrid silane-crosslinking polymers is the absence of potential harmful chemicals, such as isocyanates and solvents. Two hybrid formulations were characterized by thermo-mechanical analysis (TMA) and glued wood product elasticity is discussed in this brief original.
Particleboard I.B. forcast by TMA bending in UF adhesives curing
Materials and methods Six urea-formaldehyde resins of molar ratios of U:F of respectively 1:1.1, 1:1.2, 1:1.3, 1:1.5, 1:1.8, and 1:2.0 were prepared as follows: To a urea/formaldehyde concentrate (formurea) containing 23% urea and 57% formaldehyde in water was added 22% NaOH to set the pH between 8.3-8.5. The temperature is raised in 50 minutes to 90 ~ maintaining the pH between 7.3-7.6 by small additions of 22% NaOH, and maintained at 90 ~ for approx 20 minutes. The pH decreases by itself and is maintained not lower than 4.7-5.1 and the temperature increased to 98 ~ The reaction is stopped when a water tolerance point of 170% is reached in the case of all resins, by cooling to 40 ~ the second urea added, the pH readjusted to 8.7 with NaOH, and the resin left to mature overnight at 40 ~ The ratio of second urea to initial urea for the preparations above was in the same order as above of 0.35, 0.36, 0.38, 0.41, 0.47 and 0.52 respectively. All the resins were at solids contents in the range 53.3%-54.9%. The resins were then tested by thermomechanical analysis (TMA) by procedures already reported (Pizzi, 1997, Kamoun et al 1998, Garcia and Pizzi 1998), after addition on resin solids of 2% NH4C1 as a 25% solution, by placing 30 mg of glue mix between two plys of beech wood to form a joint of 21 x 6 • 11.5 mm dimension which is tested in three points bending for a span of I8 mm, subjected to an alternating force of 0.1/0.5 N with a 6 s/6 s cycle, at a constant heating rate of !0 s/ minute, from 40 ~ to 250 ~ The min imum value of the deflection corresponding to the tighter network formed by the adhesive on curing is then measured. Duplicate one layer laboratory particleboard of 350 x 310 x 14 mm dimensions were then produced by adding 12% UF resin solids on dry wood particles(to make sure that results good enough to notice a difference would be obtained) pressed at a max pressure of 32 kg/ cm 2 followed by a descending pressure cycle, at 195 ~ and for a pressing time of 4.4 minutes (19 s /mm panel thickness). All the panels had densities comprised between 730 and 740 kg/cm 3. The panels, after light sanding, were tested for dry internal bond (I.B.). The results obtained are shown in the Table.
Evolution of carbide precipitates in Hastelloy N joints during welding and post weld heat treatment
Abstract The effects of welding and post weld heat treatment (PWHT) on the morphology, composition and lattice parameter of the precipitates in the welding joints of Hastelloy N alloy have been investigated. Joint samples were prepared using a gas tungsten arc welding process with ERNiMo-2 fillers, and then solid-solution treated at 1100 °C for 20 min. After welding, eutectic M6C carbides can be observed in the heat affected zones (HAZ) and weld zones (WZ). These eutectic M6C carbides become spheroidized during the following PWHT. The concentration of Si decreases during the transformation from the primary ones to eutectic ones, and then increases during the spheroidizing process. The total concentration of Si + Cr in M6C carbides remains stable during welding and PWHT. At the same time, the heat leads to the outward diffusion of Mo from the M6C carbides, which results in a decrease of the lattice parameter.