共查询到18条相似文献,搜索用时 265 毫秒
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通过调控甲醛与尿素摩尔比, 降低脲醛树脂胶黏剂中游离甲醛的含量, 以生物质玉米芯为原材料, 用碱液提取得到的碱木质素溶液与甲醛和尿素进行三元逐步共聚, 弥补降低醛脲比带来的胶合强度的快速下降问题. 以降低游离甲醛含量同时兼顾胶合强度为原则进行探索, 得到最佳实验条件为甲醛与尿素摩尔比(F/U)为0.91∶1, 木质素添加量为20%(质量分数), 在此条件下木质素-尿素-甲醛共聚树脂(LUF)胶合强度为0.99 MPa, 游离甲醛含量为0.26%. 对共聚树脂进行了结构表征, 表明木质素参与到反应中, 并能提高树脂的热稳定性和耐水性, 同时对反应的机理进行了讨论. 相似文献
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尿素甲醛聚合反应中的沉淀现象 总被引:5,自引:0,他引:5
首次研究了尿素甲醛聚合反应中的沉淀现象以及不同反应条件对沉淀产物半结晶结构特征的影响. 定量分析结果显示以尿素甲醛物质的量之比1.0∶1.0为基础, 增加甲醛用量沉淀产物质量减少, 但当增加尿素用量时沉淀质量为一定值. 根据聚合产物线型结构对应的反应计算, 沉淀产物收率接近100%. 改变体系酸性和反应物总量等条件也可得到类似的定量反应结果. 沉淀产物中特征官能团的伸缩振动光谱随着反应条件的变化而变化. 当增加甲醛用量时, 官能团振动吸收强度明显减弱; 增加尿素用量时吸收强度略有增加. 改变体系酸性和反应物总量同样可对产物的振动光谱产生影响. 这种吸收强度的变化与XRD表征所得样品结晶性变化规律完全一致, 这表明尿素甲醛聚合反应中的沉淀现象是一种线型分子之间氢键相互作用引起的半结晶聚积过程. 相似文献
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新颖表面结构的脲醛树脂-聚丙烯酰胺复合微球的制备研究 总被引:2,自引:0,他引:2
将高分子微凝胶模板法应用于制备脲醛树脂[Urea-formaldehyde resin (UF Resin)]-聚丙烯酰胺[Polyacrylamide (PAM)]有机-有机复合微球材料. 以PAM高分子微凝胶为模板, 通过控制甲醛和尿素的缩聚反应在反相悬浮体系中进行, 制备得到了具有新颖表面形貌的脲醛树脂-聚丙烯酰胺[UF Resin/PAM]有机-有机复合微球, 利用扫描电子显微镜(SEM)、热重分析(TGA)、红外(FT-IR)等手段对复合微球进行了表征. 实验结果表明, 复合微球的表面形貌与甲醛和尿素溶液的pH值、甲醛和尿素溶液的浓度、甲醛和尿素的摩尔比、模板的组成等因素有关. 可以预期, 本研究方法将为制备具有特异表面形貌的有机-有机复合微球材料提供了一条有效的途径. 相似文献
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本文在存在十二烷基苯磺酸钠时利用正硅酸乙酯水解液中尿素和甲醛的结晶性聚合反应合成得到了氧化硅微球。首次考察了尿素和甲醛的物质的量比、尿素和甲醛的总用量、正硅酸乙酯(TEOS)用量、酸用量、以及十二烷基苯磺酸钠用量对所得氧化硅微球结构和形貌特征的影响。适当选择这些用量范围可以得到结构稳定、分散均匀的氧化硅微球。在微球生长中尿素和甲醛的量不足时,其突出的结晶性聚合与氧化硅杂化反应进程相互影响,导致了氧化硅微球核壳结构的形成。酸用量增加使氧化硅微球的孔径分布从复杂的双峰转变成均匀的单峰。表面活性剂的使用使氧化硅微球的孔分布从0~80 nm范围内的连续分布转化成单一分布。这些结果对正硅酸乙酯水解液直接合成氧化硅微球方法的推广和应用具有重要指导意义。 相似文献
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高浓度甲醛废水预处理工艺研究 总被引:1,自引:0,他引:1
采用“尿素缩合-粉煤灰吸附-Fenton氧化”复合工艺来处理高浓度甲醛废水,对影响甲醛去除率的因素进行了试验探讨,并确定了工艺优化条件.用该工艺处理高浓度甲醛废水,甲醛的总去除率可达到99%以上,能满足最终生化处理的要求. 相似文献
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脲醛树脂合成反应过程的FTIR研究 总被引:13,自引:0,他引:13
利用傅里叶变换红外(FTIR)光谱研究了脲醛树脂合成中不同结构形成和变化情况. 对FTIR谱图解析和分析的结果表明, 在脲醛树脂预聚物合成过程中, 随着甲醛与尿素反应的进行, 红外谱图特征峰发生有规律的变化, 酰胺II带特征峰波数逐渐低移, 有更多羟甲基、醚键和—NHCH2—结构基元形成, 固化反应使上述结构基元相应减少. 着重分析了不同甲醛与尿素摩尔比(nF/nU)下尿素与甲醛反应产物结构的变化, 随nF/nU的增加, 酰胺II带特征峰波数逐渐低移, 碱性条件下醚键和—NHCH2—结构基元明显增加, 在较强酸性条件下Uron环、亚甲基桥和羟甲基显著增加, 而—NHCH2—结构基元含量下降. 相似文献
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赵庚祝宝东邹楠楠王鉴 《高分子通报》2023,(9):1136-1146
本文从微胶囊壁材出发,重点介绍了石蜡基/高分子、无机和高分子-无机杂化壳微胶囊的制备及应用,并总结了上述微胶囊的优势和不足。其中石蜡基/高分子壳微胶囊的壁材包括三聚氰胺-甲醛树脂、脲醛树脂、三聚氰胺-甲醛-尿素树脂、聚氨酯树脂、丙烯酸树脂等,石蜡基/无机壳微胶囊的壁材包括二氧化硅、二氧化钛、碳酸钙、氧化锌等,石蜡基/高分子-无机杂化壳的壁材包括三聚氰胺-甲醛树脂、三聚氰胺-甲醛-尿素树脂、丙烯酸树脂等与二氧化钛、二氧化硅等无机粒子复合。并对石蜡基微胶囊相变材料的未来发展方向和应用前景进行展望,以期为今后研究提供借鉴。 相似文献
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Suzana Samaržija-Jovanović Vojislav Jovanović Sandra Konstantinović Gordana Marković Milena Marinović-Cincović 《Journal of Thermal Analysis and Calorimetry》2011,104(3):1159-1166
The thermal stability of pure urea–formaldehyde resin (PR) and modified urea–formaldehyde (UF) resins with hexamethylenetetramine-HMTA
(Resin 1), melamine-M (Resin 2), and ethylene urea (EU, Resin 3) including nano-SiO2 was investigated by non-isothermal thermo-gravimetric analysis (TG), differential thermal gravimetry (DTG), and differential
thermal analysis (DTA) supported by data from IR spectroscopy. Possibility of combining inorganic filler in a form of silicon
dioxide with UF resins was found investigated and percentage of free formaldehyde was determined. The shift of DTG peaks to
a high temperature indicates the increase of thermal stability of modified UF resin with EU (Resin 3) which is confirmed by
data obtained from the FTIR study. The minimum percentage (6%) of free formaldehyde was obtained in Resin 3. 相似文献
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Moon G. Kim 《Journal of polymer science. Part A, Polymer chemistry》1999,37(7):995-1007
Selected synthesis parameters of typical wood adhesive‐type urea–formaldehyde (UF) resins were examined using the 13C NMR spectroscopy. The monomeric hydroxymethylureas and methylene–ether derivatives formed in the initial alkaline reaction polymerize in the subsequent acidic reaction by forming methylene bonds and cleaving some hydroxymethyl groups as formaldehyde. For typical resin syntheses at F/U ratio of 2.10, the resulting UF polymer is found to be a number‐averaged pentamer having 3.25 polymer chain branches with about 80% of chain ends bonded to hydroxymethyl groups and the rest being free amide groups. When the second urea is added during the cooling period, about 67% of hydroxymethyl groups cleave from the UF polymeric components and the freed formaldehyde reacts with second urea to form monomeric hydroxymethylureas. This hydroxymethyl group move is suppressed when the second urea is added at low temperatures, suggesting that wood adhesive‐type UF resins are composed of monomeric and polymeric UF components having hydroxymethyl functional groups in varying proportions. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 995–1007, 1999 相似文献
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K. Siimer P. Christjanson T. Kaljuvee T. Pehk I. Saks 《Journal of Thermal Analysis and Calorimetry》2009,97(2):459-466
Urea–formaldehyde (UF) and phenol–formaldehyde (PF) resins are the most widely used wood adhesives. The first stage in resin
manufacturing is the formation of methylol derivatives which polycondensation leads to building the tridimensional network.
Understanding the behaviour of methylol compounds in curing provides useful information for developing appropriate resin structures.
Thermal behaviour of N,N′-dihydroxymethylurea, 2- and 4-hydroxymethylphenols, urea and phenol as model compounds for UF, PF and phenol–urea–formaldehyde
(PUF) resins was followed by TG-DTA method. The measurements were carried out by the labsys instrument Setaram at 30–450 °C in nitrogen flow. The characteristic signals for model compounds and for some reaction mixtures
were measured by high resolution 13C NMR spectroscopy. 相似文献
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以九水合硝酸铁为原料, 利用改进的聚合诱导胶体聚集(PICA)的方法制备出三维网络状多级孔结构氧化铁(HPH). 此结构的制备关键是在合成过程中尿素和甲醛聚合生成脲醛树脂(UF). 脲醛树脂一方面在铁的羟基氧化物生长过程中与之杂化形成杂化产物Fe-UF, 另一方面则进一步聚合, 形成脲醛树脂微球(UFM). 脲醛树脂微球作为模板诱导杂化产物Fe-UF在其表面的聚集. 微球与微球之间则由于表面存在的脲醛树脂间的聚合会相互交联形成网络状结构. 经过煅烧处理后, 脲醛树脂及脲醛树脂微球的分解导致不同尺寸孔结构的生成. 光催化研究结果表明, 产物对罗丹明B的降解效率是商用纳米氧化铁的4倍. 相似文献
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Kadri Siimer Tiit Kaljuvee Tõnis Pehk Ilmar Lasn 《Journal of Thermal Analysis and Calorimetry》2010,99(3):755-762
Thermal behaviour of industrial UF resins modified by low level of melamine was followed by TG-DTA technique on the labsys TM instrument Setaram together with the 13C NMR analysis of resin structure and testing boards in current production at Estonian particleboard factory Pärnu Plaaditehas AS. DTA curve of UF resin which has been cocondensed during synthesis with even low level of melamine shows the shift of condensation exotherm and water evaporation endotherm to considerable higher temperatures. The effect of melamine monomer introduced to UF resin just before curing was compared. The effect of addition of urea as formaldehyde scavenger was studied. 相似文献
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Synthesis and Characterization of Melamine Formaldehyde Resins for Decorative Paper Applications 下载免费PDF全文
S. Ullah M. A. Bustam F. Ahmad M. Nadeem M. Y. Naz M. Sagir A. M. Shariff 《中国化学会会志》2015,62(2):182-190
Melamine‐formaldehyde (MF) resins of improved environmental compatibility were synthesized at different molar ratios, temperature and pH. Five molar ratios of melamine and formaldehyde: 35:65, 36.5:63.5, 38.3:61.7, 41.1:58.9 and 42.4:58.6 were used to synthesize the corresponding resins. The prepared samples were characterized by using molecular weight determination viscometery, field emission scanning electron microscopy and thermogravimetric analysis. It was noticed that the solid content in the resin increases with an increase in pH. The maximum percentage of the solid content (51 %) was obtained for pH of 8.5 and temperature range of 95–98 oC. The refractive index of the final product was found increasing with an increase of melamine concentration in the resin. A similar trend was noticed in molecular weight of the resins with an increase in monomer yield. The maximum molecular weight of 114218 was obtained from the sample synthesized with MF molar ratio of 42.4:58.6. 相似文献
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Arif Nuryawan Byung-Dae Park Adya P. Singh 《Journal of Thermal Analysis and Calorimetry》2014,118(1):397-404
This study was undertaken to compare thermal cure kinetics of urea–formaldehyde (UF) resins, in both liquid and solid forms as a function of formaldehyde/urea (F/U) mole ratio, using multi-heating rate methods of differential scanning calorimetry. The requirement of peak temperature (T p), heat of reaction (ΔH) and activation energy (E) for the cure of four F/U mole ratio UF resins (1.6, 1.4, 1.2 and 1.0) was investigated. Both types of UF resins showed a single T p, which ranged from 75 to 118 °C for liquid resins, and from 240 to 275 °C for solid resins. As the F/U mole ratio decreased, T p values increased for both liquid and solid resins. ΔH values of solid resins were much greater than those of liquid resins, indicating a greater energy requirement for the cure of solid resins. The ΔH value of liquid UF resins increased with decreasing in F/U mole ratio whereas it was opposite for solid resins, with much variation. The activation energy (E a) values calculated by Kissinger method were greater for solid UF resins than for liquid resins. The activation energy (E α ) values calculated by isoconversional method which showed that UF resins in liquid or solid state at F/U mole ratio of 1.6 followed a multi-step reaction in their cure kinetics. These results demonstrated that thermal curing behavior of solid UF resin differed greatly from that of liquid resins, because of a greater branched network structure in the former. 相似文献
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To understand the influence of formaldehyde/urea (F/U) mole ratio on the properties of urea–formaldehyde (UF) resins, this study investigated hardness of cured UF resins with different F/U mole ratios using a nanoindentation method. The traditional Brinell hardness (HB) method was also used for comparison. The HB of cured UF resin films with different F/U mole ratios was determined after exposing the films to different post-curing temperatures. The nanoindentation method was employed for these films to measure Meyer hardness (HM) and reduced modulus (Er) which have been used to calculate the elastic modulus (Es) of cured UF resins. As the F/U mole ratio decreased, the HB decreased continuously, indicating a less rigid network structure in low F/U mole ratio UF resins. The higher the post-curing temperature, the greater the value of HB. The HM value also showed a similar trend as a function of F/U mole ratio. However, the Er and Es did not show a consistent trend as exhibited by HM and HB. Both HM and Er showed much greater variation in the coefficient of variation (COV) at lower F/U mole ratios 1.0 and 1.2, indicating a more heterogeneous composition of these resins. Linear relationships between HM and Er indicate that heterogeneity of the surface composition of samples contributes greatly to variations in the measured values. This variability is discussed in terms of crystal structures present in the cured UF resins of low F/U mole ratios. 相似文献