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1.
Ida Poljanšek Blaž Likozar Nataša Čuk Matjaž Kunaver 《Wood Science and Technology》2013,47(2):395-409
The objective of this research was to investigate the effect of liquefied wood (LW) on the cure kinetics and network properties of melamine–urea–formaldehyde (MUF) resins by differential scanning calorimetry. The MUF/LW compounds exhibited two distinct cross-linking processes. It can be assumed that there did not appear to be a coreaction of the MUF with the LW. The overall apparent activation energies (E a) of the curing reactions were calculated using the Kissinger equation. An nth-order kinetic model was used to describe the cross-linking of MUF/LW compounds, of various compositions, cured at different heating rates. The E a values for the cross-linking process of the MUF/LW compounds predominantly tended to be approximately 80 and 71 kJ mol?1 for MUF and LW, respectively. The apparent reaction orders of the MUF cross-linking process of the MUF/LW compounds were in the range 1–2, whereas the n values of the LW were approximately unity or less, which hints to there being a more complex mechanism of this process. 相似文献
2.
Fire retardancy of melamine-modified urea–formaldehyde resin (MUF) containing intumescent fire-retardant ammonium polyphosphate (APP) (MUF/APP) was conducted by cone calorimeter with surface treatment of medium density fiberboard (MDF). The results showed that the six MUF resins synthesized with different F/(M + U) and M/U molar ratios containing APP significantly improved the fire retardancy of the MDF by prolonging ignition time, reducing heat release rate and total heat release, and decreasing mass loss rate. The fire-retardant properties of the six synthesized MUF/APP acted differently even though each MUF resin containing the same mass ratio of APP. The melamine content in the MUF should not be too high, otherwise it would decrease the fire-retardant properties of MUF/APP. Based on this study, the higher the APP amounts, the better the fire-retardant performance of the resin was. The fire retardancy of MUF/APP increased with the increase in the amount of glue that spread on the material surface. However, only the amount of glue spread exceeded 250 g/m2, whereas the ability of MUF/APP in inhibiting heat release did not increase significantly any longer. 相似文献
3.
More than 200,000 tons of scallop shells are disposed annually alone in Japan. Nanoparticles derived from scallop shells have the potential to adsorb gaseous formaldehyde; therefore, such discarded shells have now been tested as additive filler in plywood adhesive by mixing high specific surface area, urea-modified shell nanoparticles with a resorcinol–formaldehyde resin. With this procedure, it was found that the emission of formaldehyde from the resulting plywood could be substantially reduced. The urea-modified scallop shell nanoparticles were prepared by two different methods: (1) a dry method where the shells were treated by planetary ball-grinding under ambient conditions—a completely dried powder was obtained after addition of the surface-modifying urea solution; (2) a moist method by treating dry ground shell particles in a wet grinding process with the urea solution, followed by centrifugation to obtain a paste. The specific surface area of the nanoparticles obtained by both treatments was 42 ± 3 m2/g. Measurement of the subsequent formaldehyde emission showed that the addition of the modified scallop shell nanoparticles substantially reduced the formaldehyde emission from plywood. The reduction of the specific mass uptake of urea depends on the nanoparticles which especially was the case when resins containing nanoparticles processed by the moist method were used. 相似文献
4.
Preparation of phenol formaldehyde resin from phenolated wood 总被引：2，自引：0，他引：2
The technique for preparing phenol formaldehyde resin from phenolated wood (PWF) and its characters were studied and analyzed.
Poplar (Populus spp) wood meal was liquefied by phenol in the presence of sulfuric acid as a catalyst. After the liquefied products were cooled,
alkaline catalyst and formaldehyde were added. The mixture was kept at (60±2)°C for 1h and then was heated to (85±2)°C for
1h. The influence of molar ratio of formaldehyde to phenol (F/P) was investigated. The results showed when the molar ratio
of formaldehyde to phenol was over 1.8, the PWF adhesives had high bond quality, bond durability and extremely low aldehydes
emissions.
Foundation item: The research was supported by Sino-Japanese Technical Cooperation Project (2-1-b) and the key technologies R & D Program
for the 10th Five-Year Plan (325-11).
Biography: LI Gai-yun (1974-), female, Assistant professor in Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing
100091, P. R. China
Responsible editor: Zhu Hong 相似文献
5.
To produce a highly stable wood-based product with increased mechanical properties, phenol formaldehyde (PF) resin impregnation
was combined with the viscoelastic thermal compression (VTC) process. Dimensional stability and bending stiffness were evaluated.
Two PF resins with weight average molecular weights of 172 and 780 were studied at three different concentrations, 5, 10 and
20%. After 24-h room temperature water soak and 2-h boil, both PF treatments at all concentration levels showed high levels
of dimensional stability compared to non-impregnated VTC processed controls. The higher molecular weight PF provided greater
stability with an average thickness swell value of 12% compared to 20 and 37% for the lower molecular weight PF resin treatment
and control, respectively. High anti-swelling efficiency values were recorded for both low and high molecular weight resins,
implying these modifications were effective at reducing the volumetric swelling which occurred in the unmodified control.
PF treatments were also extremely effective at reducing irreversible swelling. The low and high molecular weight resin treatments
had 1/5th and 1/7th the irreversible swelling than the unmodified VTC processed controls, respectively. All dimensional stability
values improved as resin concentrations increased. Both resin types at all concentration levels reduced Young’s modulus. 相似文献
6.
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. 相似文献
7.
The effect of addition of Acacia mangium bark powder on the thermosetting processes of two commercial phenol resins, PF-A and PF-B, was examined by bond strength
test, torsional braid analysis, and differential scanning calorimetry. When the bark powder was added to PF-A, the bond strength
of plywood pressed at 110°C increased and was comparable to that of plywood pressed at 120 and 130°C. However, when the bark
powder was added to PF-B, the bond strength of plywood pressed at 110°C was still lower than that of plywood pressed at 120
and 130°C. The relative rigidity and loss tangent of PF-A cured with the bark powder obtained by heating at 100°C were comparable
to those at 120 and 140°C, and the reaction enthalpy was increased by bark powder addition. In contrast, chemical reactions
for cured PF-B were not enhanced by bark powder addition. 相似文献