Influence of preparation parameters on the CHT curing diagrams of MUF polycondensation resins

Lignocellulosic substrates such as wood have been found to have a marked modifying influence on both lower‐temperature and higher‐temperature zones of TTT and CHT diagrams during hardening of formaldehyde‐based polycondensates. While the modifying influence of the substrate has been described, the modifying influence of some of the most important manufacturing parameters of the resins on the CHT diagram, not having been previously investigated, are explored here and clear trends are shown. In the case of melamine–urea–formaldehyde (MUF) resins for wood adhesives, the molar ratio (M+U):F appear to be the dominant parameter influencing the relative position of gel and vitrification curves in relation to each other. The ratio of melamine to urea does not appear to have any effect on the relative position of the curve, lacking any clear trend, at least at the higher (M+U) molar ratio of 1:1.9 used for this series of resins. In the case presented for the first time, the influence of resin manufacturing parameters on CHT curing diagrams was studied in combination with the modifications introduced by the substrate. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2821–2825, 2001     

Copolymerization in UF/pMDI adhesives networks

Kinetic evidence in thermomechanical analysis experiments and carbon‐13 nuclear magnetic resonance spectroscopy (¹³C NMR) evidence indicates that the strength of a joint bonded with UF (urea–formaldehyde)/polymeric 4,4'‐diphenylmethane diisocyanate (pMDI) glue mixes is improved by coreaction of the methylol groups of UF resins with pMDI to form a certain number of methylene cross‐links. The formation of these methylene cross‐links is predominant, rather than formation of urethane bridges which still appear to form but which are in great minority. This reaction occurs in presence of water and under the predominantly acid hardening conditions, which is characteristic of aminoplastic resins (thus, in presence of a hardener). Coreaction occurs to a much lesser extent under alkaline conditions (hence, without UF resins hardeners). The predominant reaction is then different in UF/pMDI adhesive systems than that observed in phenol‐formaldehyde (PF)/pMDI adhesive systems. The same reaction observed for UF/pMDI system at higher temperatures has also been observed in PF/pMDI systems, but only at lower temperatures. The water introduced in the UF/pMDI mix by addition of the UF resin solution has been shown not to react with pMDI to an extent such as to contribute much, if at all, to the increase in strength of the hardened adhesive. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3681–3688, 2002     

Lignocellulosic substrates influence on TTT and CHT curing diagrams of polycondensation resins

Lignocellulosic substrates such as wood were found to have a marked modifying influence on a well‐defined region of CHT diagrams during hardening of phenol–formaldehyde (PF) and urea–formaldehyde (UF) polycondensates. This was ascribed to more complex resin phase transitions due to resin/substrate interactions peculiar to these substrates. The chemical and physical mechanisms of the interactions of the resin and substrate causing such CHT diagram modifications are presented and discussed. The Di Benedetto equation describing the glass transition temperature T_g of the system as a function of the resin degree of conversion p has been slightly modified to take into account the modified CHT diagram. The modified CHT diagram can be used to good effect to describe the behavior of polycondensation resins when used as wood adhesives during their curing directly into the wood joint. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 915–925, 1999     

Variation of MUF and PMUF resins mass fractions during preparation

The variation of molecular mass distribution with the progress of the reaction was studied for the following: (i) sequential‐type melamine–urea–formaldehyde (MUF) resin formulations in which the sequence of addition of chemicals follows well‐defined species reactivity principles; (ii) a nonsequential MUF formulation in which simultaneous melamine and urea competition for formaldehyde yields a MF resin cocondensed with small amounts of urea. This resin became soaked with reacted and unreacted monomeric urea species. (iii) A PMUF resin, namely a MUF resin with a small proportion of phenol (7.8% by weight on melamine and urea) cocondensed with the main MUF fraction. All the formulations used were industrial resins formulations in current use. Development and variation of molecular mass fractions, from which performance and other useful resin parameters depend, have been found to depend on the type of resin formulation used for these type of aminoplastic resins. The two very different MUF resin formulations yielded different variations in molecular mass fractions during the progress of the reaction and during the so‐called ambient temperature “maturing” of the resin. The PMUF resin also showed both similar and different fractions present during manufacturing and during short term ageing at ambient temperature. While similarities in recurrent fractions and in trends are common to all the three different formulations, differences between them are also clearly observed. A major proportion of the reaction of some of the aminoplastic resins examined also occurs on ageing (i.e.“maturing” of the resin at ambient temperature), this appearing to be an essential phase of the resin preparation process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4842–4855, 2006     

Long‐term development of thermophysical and mechanical properties of cold‐curing structural adhesives due to post‐curing

The long‐term changes in the thermophysical and mechanical properties of a cold‐curing structural epoxy adhesive were investigated by accelerating the curing reaction by post‐curing at elevated temperatures. Experimental data concerning the glass transition temperature for periods of up to 7 years and tensile strength and stiffness measurements could be extrapolated for a period of up to 17 years. An existing model for the long‐term development of concrete properties was modified for the prediction of the long‐term mechanical properties of adhesives. The applicability of the acceleration procedure and the new model was confirmed by several verification procedures. Structural adhesives exhibit significant increases in glass transition temperature, strength and stiffness over the long term provided that joints are adequately sealed and protected from humidity and UV radiation. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Examination of selected synthesis parameters for wood adhesive‐type urea–formaldehyde resins by 13C NMR spectroscopy. III

The varying polymer structures of wood adhesive‐type urea–formaldehyde resins resulting from different formaldehyde/first urea (F/U₁) mole ratios used in the first step of resin manufacture were investigated using ¹³C. As the F/U₁ mole ratio decreased progressively from 2.40 to 2.10 and to 1.80, the viscosity increase due to polymerization during resin synthesis became faster and resulted in decreasing side‐chain branches and increasing free urea amide groups in the resin structure. The resultant UF resins, with the second urea added to an overall F/(U₁ + U₂) of 1.15, showed viscosity decreases when heated with stirring or allowed to stand at room temperature that were also characteristic with the F/U₁ mole ratios used in resin synthesis. The formaldehyde emission levels of particleboards bonded with the freshly made UF resins showed relatively small but similarly characteristic variations. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2800–2814, 2001     

Thermoplastic modification of urea–formaldehyde wood adhesives to improve moisture resistance

Urea–formaldehyde (UF) resins are prone to hydrolytic degradation, which limits their use to indoor applications. This study examined the modification of UF resin with various thermoplastics as a means to increase the moisture resistance of the adhesive. UF adhesives were modified in situ with various hydrophobic and hydrophilic thermoplastic formulations, using either polar or nonpolar initiators. Unmodified and modified UF resins were characterized in terms of viscosity, pH, and gel time in their prepolymer suspension state. Cured solid UF resin plaques were prepared to isolate moisture sorption effects of the cured UF resin from that of the wood component in composites, which dominates their moisture uptake. Relative crosslink density and moisture sorption tests were run on cured UF resin plaques. Results indicated that viscosity increased after modification in most cases, with higher viscosities resulting from formulations using an acidic (polar) initiator. In all cases, activation energies of the curing reactions of thermoplastic‐modified UF suspensions were lower than the unmodified UF. High relative crosslink density compared to the unmodified UF was found for one sample, which correlated well with lower overall moisture sorption. Higher relative crosslink density of cured UF resin plaques appeared to be an indicator of lower moisture uptake. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4222–4229, 2006     

Effects of formaldehyde to urea mole ratio on thermal curing behavior of urea–formaldehyde resin and properties of particleboard

As a part of abating the formaldehyde emission (FE) of urea–formaldehyde (UF) resin, this study was conducted to investigate the effects of formaldehyde to urea (F/U) mole ratio on thermal curing behavior of UF resins and properties of PB bonded with them. UF resins synthesized at different F/U mole ratios (i.e., 1.6, 1.4, 1.2, and 1.0) were used for the manufacture of PB. Thermal curing behavior of these UF resins was characterized using differential scanning calorimetry (DSC). As the F/U mole ratio decreases, the gel time, onset and peak temperatures, and heat of reaction (ΔH) increased, while the activation energy (E_a) and rate constant (k) were decreased. The amount of free formaldehyde of UF resin and FE of PB prepared decreased in parallel with decreasing the F/U mole ratio. The internal bond strength, thickness swelling, and water absorption of PB was slightly deteriorated with decreasing the F/U mole ratio of UF resins used. These results indicated that as the F/U mole ratio decreased, the FE of PB was greatly reduced at the expense of the reactivity of UF resin and slight deterioration of performance of PB prepared. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1787–1792, 2006     

Examination of selected synthesis and room‐temperature storage parameters for wood adhesive‐type urea–formaldehyde resins by 13C‐NMR spectroscopy. IV

Typical particleboard wood‐adhesive urea–formaldehyde (UF) resins, synthesized with formaldehyde/first urea (F/U₁) mol ratios of 1.80, 2.10, and 2.40 and the second urea added to an overall F/U ratio of 1.15, in weak alkaline pH, were allowed to stand at room temperature over a period of 50 days. ¹³C‐NMR of time samples taken over the storage period showed gradual migration of hydroxymethyl groups from the polymeric first‐urea components to the monomeric second‐urea components and also an advancing degree of polymerization of resins by forming methylene and methylene ether groups involving the second urea. These phenomena that varied with the F/U₁ mol ratios used in the resin syntheses due to the varying polymer branching structures resulted in the first step of resin synthesis. Varying viscosity decreases and increases of the resins also occurred. Due to these chemical and physical changes, the particleboards that bonded with the sampled resins showed varying bond strength and formaldehyde‐emission values, indicating process optimizations possible to improve bonding and formaldehyde‐emission performances. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1155–1169, 2001     

建筑结构胶粘剂的发展和展望

建筑结构胶粘剂经过30多年的发展已成为重要的结构粘接材料。本文综述了建筑结构胶粘剂发展与技术进步。并针对研发、原材料、生产及标准中存在的问题,探讨了其发展方向。     

Optimal preparation and characterization of poly(urea–formaldehyde) microcapsules

Microcapsules with epoxy curing agent were successfully prepared by an in‐situ polymerization route with epoxy resin and poly‐(urea–formaldehyde) as core and shell materials, respectively. The synthetic conditions were optimized by a comprehensive investigation on raw materials consumption, size distribution, and surface morphology. Preparation of microcapsules with high wrap ratio was also demonstrated. The as‐synthesized microcapsules were studied using various characterizations techniques, including optical microscope, fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and contact angle meter. Spherical microcapsules (size: ～ 60 μm) with smooth surface were obtained when the stirring rate was 400 rpm and the amount of core materials is 76 wt %. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

建筑结构胶的耐湿热老化性能研究

耐湿热老化是建筑结构胶的重要性能指标,正在受到越来越多的关注。研究了不同种类的固化剂对改性环氧树脂类建筑结构胶的耐湿热老化性能的影响,同时也对增韧剂、无机填料及助剂等因素进行了探讨。采用自制的固化剂所配制的建筑结构胶耐湿热老化性能优良,完全满足国家标准的要求。     

Resol‐type phenolic resin from liquefied phenolated wood and its application to phenolic foam

A liquefied wood‐based resol resin was prepared with excellent yield by a reaction of liquefied wood and formaldehyde under alkaline conditions. The effects of various reaction parameters on the extent of the yield of the resol resin, unreacted phenol content, and viscosity were investigated. Milder resol resinification conditions were required as compared to those used in conventional methods. The liquefied wood‐based resol resin was successfully applied to produce phenolic foam using appropriate combinations of foaming agents. Diisopropyl ether with a relatively higher boiling temperature was suitable for the foaming of liquefied wood‐based resol resin. Hydrochloric acid and poly(ethylene ether) of sorbitan monopalmitate were used as a catalyst and a surfactant, respectively. The obtained foams showed satisfactory densities and compressive properties, comparable to those of foams obtained from conventional resol resin. Foams with low density were obtained by the blending of liquefied wood‐based resol resin and conventional resol resin. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 468–472, 2002; DOI 10.1002/app.10018     

F-51／DDS／PES三元树脂体系的固化反应动力学研究

结合测量凝胶化8寸间以及粘度与温度的关系,用差示扫描量热法(DSC)研究了F-51／DDS／PES三元树脂体系的固化反应动力学,计算出了表观活化能△E、碰撞因子A和反应级数n,并结合傅里叶变换红外光谱对反应机理进行了探讨,指出了反应过程中多元胺类固化剂分步反应对固化反应的进行有重要促进作用,为进一步研究耐高温复合材料、胶粘剂等奠定了基础。     

曼尼希改性二乙烯三胺环氧建筑胶固化剂的制备

选用苯酚（P）、甲醛（F）对二乙烯三胺（DETA）进行曼尼希反应改性,研究了产物黏度、胺值与原料配比的关系。将改性的固化剂与环氧树脂E51进行配胶浇注,研究了胶体的力学性能与潮湿环境下的粘接性能。结果表明,P、DETA与F物质的量比[n（P）：n（DETA）：n（F）]=1．5：1．5：1．5的产物综合性能最佳。该固化剂黏度适宜（6542mPa·s）,与E51配胶浇注后,拉伸强度为40MPa,压缩强度达80MPa,潮湿环境下的钢一钢剪切强度为9．2MPa,与混凝土的粘接拉伸强度达47MPa,为混凝土内聚破坏。     

pH和碱度对同步厌氧生物脱氮除硫工艺性能的影响

采用UASB反应器研究了pH和碱度对同步厌氧生物脱氮除硫工艺性能的影响。控制进水pH在7.5～8.0之间,反应器的最大容积硫化物和硝酸盐去除速率分别为2.96 kg·(m³·d)^-1和0.47 kg·(m³·d)^-1（分别以硫元素、氮元素计）,反应过程产碱及残留硫化物,均会导致反应液pH值过高（9.11±0.38）,引发高负荷时工艺失稳。控制反应液pH在7.0±0.1范围,容积硫化物和硝酸盐去除速率分别可达4.78 kg·(m³·d)^-1和0.99 kg·(m³·d)^-1,容积效能高于控制进水pH时的相应值。要维持反应所需的中性条件,碱度宜控制在（454.1±40.5）mg ·L^-1（以CaCO₃计）。反应过程中的碱度变化（增量）可以指示反应器内主导反应的类型及其反应进度。单质硫型生物脱氮除硫反应（硫氮比为5∶2）和硫酸盐型生物脱氮除硫反应（硫氮比为5∶8）的硫化物去除量与碱度减少量之比分别为2.27和2.00,混合型生物脱氮除硫反应（硫氮比为5∶5）的硫化物去除量与碱度减少量之比为5.00。     

One‐component polyurethane adhesives for green wood gluing: Structure and temperature‐dependent creep

Creep and temperature‐dependent creep, characteristic of one‐component polyurethane adhesives for wet and green structural wood gluing are two different parameters. Testing of standards‐approved commercial polyurethane adhesives for this purpose shows that while ambient temperature creep can be avoided or at least greatly limited according to the formulation used, this is not the case for temperature‐dependent creep. The commercial adhesive formulation characteristics that minimize or enhance ambient temperature and temperature‐dependent creep are identified. Basic principles on the structure of simple polyurethane adhesives influencing temperature‐dependent creep are also identified and discussed. The higher the proportion of all hardened network nodes, the lower creep is likely to be at ambient temperature. Instead, due to segment movement and easier disentanglement with increasing temperature, the lower the proportion of covalently linked nodes and the greater the proportion of just physical entanglement nodes, the greater the temperature‐dependent creep will be. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1231–1243, 2005     

室温固化耐热环氧胶粘剂的研究进展与发展趋势

综述了室温固化耐热环氧树脂(EP)胶粘剂的研究进展与发展趋势,介绍了近年来国内外部分性能优异的室温固化耐热EP胶粘剂,指出室温固化耐热EP胶粘剂的发展趋势是耐高温、高强度、高耐久性及快速固化。     

Durability of isocyanate resin adhesives for wood. II. Effect of the addition of several polyols on the thermal properties

The thermal properties of isocyanate (IC) resins prepared with a small amount of polyether polyols and water were investigated using dynamic mechanical analysis (DMA). The bond strengths of 3‐ply plywoods glued with these polyol‐containing IC resins were also measured. The thermal stability was dramatically improved by addition of dipropylene glycol‐type polyols with molecular weights of 400 and 1000. In addition, the bond strengths in a dry condition and after aging at 250°C for 10 min exhibited high values compared with that of an IC resin cured with water alone. However, addition of the same polyol type with a molecular weight of 3000 resulted in low heat stability and low bond strength. In the case of glycerin‐type polyol with a molecular weight of 400, good thermal stability and slightly higher bond strength were obtained. When bisphenol A and pentaerythritol‐type polyols were used, not much improvement in thermal stability was achieved. The bond strengths were similar or inferior to that of an IC resin cured with water only. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1807–1814, 1999     

电解液酸碱性对电化学氧化法制备淀粉粘合剂的影响

主要探讨了电解液酸碱性对淀粉氧化程度的影响,并从理论上解释了其原因。