共查询到19条相似文献,搜索用时 140 毫秒
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采用淀粉对蜜胺树脂改性,研究了淀粉和甲醛用量、pH值及反应温度对蜜胺树脂的稳定性和游离甲醛含量的影响,结果表明,优化的工艺条件如下:淀粉用量2 g,37%甲醛溶液用量25 mL,pH值8.5~9.0,反应温度80℃,产物蜜胺树脂游离甲醛质量分数为1.8%,可在常温下存储近3个月。 相似文献
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蜜胺-脲甲醛树脂新型制法研究刘荣杰(西北大学化工系,西安710069)涂料用氨基树脂系指一种含有氨基官能团的原料与甲醛反应、再以醇类改性制得、能溶于有机溶剂的树脂,如蜜胺(三聚氰胺)甲醛树脂、脲醛树脂等,在我国,氨基树脂的生产已有20多年的历史,目前... 相似文献
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<正>(接上期)7用氨基树脂固化氨基树脂作为涂料固化剂已被关注和研究了许多年。用于涂料工业的4种不同类型的烷基化氨基甲醛树脂是:尿素、三聚氰胺、苯代三聚氰胺和甘脲甲醛树脂。氨基树脂中存在以下官能团: 相似文献
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通过在三聚氰胺-尿素-甲醛树脂(MUF)合成反应的不同阶段添加氧化木薯淀粉,制备得到了不同系列树脂,分别为MUF0、MUF1和MUF2,并对其基本性能及粘接强度进行了测试和分析。为了进一步了解氧化木薯淀粉对MUF树脂固化反应的影响,借助差示扫描量热分析仪(DSC)对树脂在不同升温速率条件下的固化特征参数及固化行为进行了表征。结果表明,在合成反应不同阶段加入氧化木薯淀粉,可有效提升树脂的粘接性能并降低树脂中的游离甲醛含量,特别是在树脂合成反应的第3阶段进行添加,效果更为显著。利用Kissinger方程对不同树脂的固化动力学参数进行分析,得到了树脂固化反应的表观活化能E a,表观频率因子A和反应级数n,并建立了固化反应动力学模型。在本试验条件下,树脂经过氧化木薯淀粉改性后,虽然固化所需活化能有不同程度的提高,但可形成更高的粘接强度。 相似文献
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脲醛树脂改性工艺中的酸度条件控制 总被引:4,自引:1,他引:4
普通脲醛树脂及氧化淀粉改性脲醛树脂的合成工艺中 ,酸度控制条件对合成产物稳定性、剪切强度、游离甲醛含量等性能影响的研究表明 ,缩合反应阶段尿素投入时体系pH值对脲醛树脂合成过程以及产物稳定性都有显著性影响。缩合阶段体系的pH值控制范围直接影响脲醛树脂的稳定性、粘合强度与游离甲醛含量。从脲醛树脂稳定性考虑 ,投入第三批尿素后的pH值应控制在 6 .0以上 相似文献
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Phenol formaldehyde resins of resol type were prepared under molar ratio phenol: formaldehyde: calcium hydroxide 1:2.7:0.1. The reaction products contained in all cases about 3.8% free formaldehyde and 1.5% free phenol. A 36% solution of formaldehyde was used for synthesis. The course of synthesis, expressed by drop of free formaldehyde contents in the reaction mixture, is presented. In aqueous resol solutions, prepared by this way, the decrease of miscibility with water was examined during storage at 10°C. It was found that the resol synthesized at lower temperature had better shelf life than that prepared at higher temperature. The presented results are of practical importance in the cases where compatibility with water is a significant processing parameter. 相似文献
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Lignin‐based chemicals, starch, and urea were used as modifiers for phenol–formaldehyde resol resins. The effects of the addition stage of the modifiers used in the synthesis of the resins and the type of modification reagent on the structures of the resins and their molar masses and reactivities were investigated. The modifications with corn starch and lignin promoted condensation; this was verified by increased molar masses and high ratios of methylene bridges to the sum of free ortho and para aromatic groups with respect to the corresponding reference resin without a modification reagent. The later the modifier was added to the resin condensation mixture, the more methylene bridges were formed with respect to the amounts of free ortho and para aromatic groups. In addition, when urea or wheat starch was added in the later condensation stage, the final condensation also reached high stages. The modifications with lignosulfonate and starch, as well as the early addition of urea, enhanced p–p′ bridge structures. The lowest condensation stage and, therefore, the highest reactivity were found when wheat starch was added with the starting reagents. The curing heat of the wheat‐starch‐modified resins decreased according to the deferred addition point of starch. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 582–588, 2003 相似文献
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A powdery product was obtained by the reaction of methylolated melamine with alkyl resorcinols to form melamine‐bridged alkyl resorcinols (MARs). The effects of the addition of this powder on the bonding strength and formaldehyde emission of urea–formaldehyde (UF) resins were investigated. Three types of UF resins with a formaldehyde/urea molar ratio of 1.3 synthesized by condensation at pH 1.0 (UF‐1.0), pH 4.5 (UF‐4.5), and pH 5.0 (UF‐5.0) were fabricated. The addition of MAR to UF‐4.5 and UF‐5.0 for bonding hardwood plywood enhanced the bonding strength and reduced formaldehyde emission. For UF‐1.0, the addition of MAR adversely affected the bonding strength. However, the UF‐1.0 resin yielded the lowest formaldehyde emission of all of the UF resins in the study. The effects of the MAR addition were related to the molecular structures of the UF resins. UF‐1.0 contained a large amount of free urea, a considerable number of urons, and a highly methylene‐linked, ring‐structured higher molecular weight fraction and had a smaller number of methylol groups. Therefore, the addition of MAR was considered to cause a shortage of the methylol groups, which in turn, led to incomplete resin curing. In contrast to UF‐1.0, UF‐5.0 contained a smaller amount of free urea and a linearly structured higher molecular weight fraction and had a larger number of methylol groups. In this case, MAR was considered to effectively react with the methylol groups to develop a three‐dimensional crosslinked polymer network to enhance the bonding strength and suppress the generation of free formaldehyde to reduce formaldehyde emission. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
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环保型脲醛树脂粘合剂合成的研究 总被引:1,自引:0,他引:1
脲醛树脂是广泛用于木材工业中一种重要的胶粘剂。对降低脲醛树脂粘合剂中游离甲醛含量的措施以及改性方法进行了探讨,并在大量的实验基础上摸索出了一套简单实用的合成工艺,根据此合成方法生产的产品具有粘度好、反应条件易控制、甲醛含量低和成本低等优点,树脂的甲醛含量达到国家室内板用粘合剂游离甲醛含量标准(GB18 587-2001)。 相似文献