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1、 I华 中 科 技 大 学 硕 士 学 位 论 文 摘 要 近几十年来，采用了不同的合成工艺去降低酚醛树脂中的游离醛量。此外，采用了橡胶弹性体，桐油，反应性液态聚合物，塑料和纤维等各种各样的增韧剂去改善酚醛树脂的韧性。然而，很多情况下，这些增韧剂可能影响酚醛树脂的耐热性，强度和模量或者其它的机械性能。在上述工作的基础上，本课题中采用了两种方法来降低酚醛树脂中的游离醛量和提高酚醛树脂的韧性。 首先，采用两步碱催化法和甲醛分批加入的方法并尝试改变合成工艺条件来降低游离醛量。结果表明：当 n(甲醛)/n(苯酚)为 1.9，n(氢氧化钠)/n(苯酚)为 3.5，反应温度为 95，反应时间为 4.5 小
2、时，游离醛量最低为 0.30(wt)。 其次，在含有低游离醛量的酚醛树脂中添加硅溶胶来提高粘结强度。纳米粒子不需要进行表面预处理，简化了工艺。用红外光谱（IR） 、拉伸剪切试验（TSS） 、扫描电镜（SEM）等对其结构、力学性能、拉伸剪切表面形貌进行了研究。实验结果表明：IR 证实在硅溶胶和酚醛树脂之间生成了新的化学键；TSS 表明当纳米 SiO2的含量为 1时，杂化材料的拉伸剪切强度和断裂伸长率分别为 1.02MPa 和 2.02%，比未改性的酚醛树脂胶粘剂提高了 50和 92。 SEM 表明拉伸剪切表面存在着大量的微裂纹从而提高了粘结强度。 环氧树脂最大的弱点是固化物的脆性大。近几十年来，
3、国内外许多学者对环氧树脂的改性做了大量卓有成效的工作，并逐步建立和形成了橡胶类弹性体改性热塑性树脂改性互穿网络（IPN）改性液晶聚合物（TLCP）改性等体系和方法。前三种方法在获得韧性改善的同时，是以材料的耐热性和其他力学性能下降作为代价的，而 TLCP 改性因成本昂贵而难以实现工业化。 本课题中用硅溶胶改善环氧树脂的拉伸剪切强度和延展性。 采用IR， TSS和SEM对该体系的结构和力学性能以及表面形貌进行了表征。结果表明：IR 证实了在硅溶胶和环氧树脂之间存在新的化学键；TSS 表明当纳米 SiO2的含量为 2时，杂化材料的拉伸剪切强度和断裂伸长率分别为 19.2MPa 和 11.4%，比未
4、改性的环氧树脂胶粘剂提高了 92和 256.3，当纳米 SiO2含量继续增大时，粘结性能下降。SEM 表明拉伸剪切表面存在着大量的微裂纹从而提高了粘结强度。 关键词：关键词：酚醛树脂；硅溶胶；环氧树脂；力学性能 II华 中 科 技 大 学 硕 士 学 位 论 文 Abstract PF resins are one of the most popular thermosetting resins and have been wildly used for many years as exterior wood adhesives. However, free phenol and free f
5、ormaldehyde, as potential carcinogens, have caused serious environmental problems. Another weakness of PF resin is its poor anti-oxidation and heat resistance owing to the existence of easily oxidated phenol hydroxide and methylene. Meanwhile, the toughness of the cured PF resin would be weakened by
6、 excessive methylene bridge structures. Efforts have been made to reduce the free formaldehyde content of PF resin and improve its toughness. In previous work, different synthesis technics were used to reduce the free formaldehyde content of PF resin. In addition, a variety of toughening agents have
7、 been used to improve the toughness of PF resin, including elastomers, oils, reactive liquid polymers, plastics, fibers and so on. However, in many cases, the toughening agents may affect the heat resistance, strength and modulus or other physical properties adversely. Recently, nanoparticles have b
8、een explored for the modification of PF resin, including nano-tube and layered silicate. These nanoparticles have a great improvement on the resistance and stiffness of PF resin, but only a little enhancement in toughness. Nano-SiO2 were also used to modify PF resin, but the processes were complex a
9、s the nano-SiO2 needed surface modification by adding other substance, such as PEG or nano-SiO2 was obtained by the sol-gel processing of alkoxysilanes. In this paper, two major attempts have been made to reduce the content of free formaldehyde and to improve the toughness of the PF resin. Firstly,
10、two steps alkaline-catalyzed and formaldehyde stage addition method was employed in the synthesis of phenol-formaldehyde resin which can reduce the content of formaldehyde, compared to the one-step alkaline-catalyzed method. Secondly, the PF resin with low content of formaldehyde was modified by add
11、ing silica sol in order to improve the adhesive strength. As a result, in daily application, the usage of adhesive and the environmental impact may be reduced. The research results showed that the adhesive strength of nano-SiO2 III华 中 科 技 大 学 硕 士 学 位 论 文 toughened PF resin composite was increased gr
12、eatly. In our work, the process of adding silica sol modified PF resin was fairly simple and nano-SiO2 had no need of the surface pretreatment, so it was convenient to industrialization. Epoxy resin is used to an engineering adhesive which is composed of epoxy resin matrix, curing agent, filling and
13、 so on. Due to its good adhesive property, low price, simple craft, it was used universally in many fields such as facility in family cars, water conservancy, space navigation fields and so on. But the biggest weakness of epoxy resin is very brittle. In recent years, many scholars home and abroad ha
14、d done large quantity of work about modification of epoxy resin, such as using rubber, thermoplastic resin, Interact Penetrating Network Polymer (IPN), Thermal Liquid Crystal Polymer (TLCP) and so on. The front three methods improved the toughness of materials at the price of the decrease of thermal
15、 resistance and other mechanical property. Meantime, Thermal Liquid Crystal Polymer (TLCP) was too expensive to industrialization. Nano-sized particle-modified EP resins have stimulated great research interest due to their unique properties, such as high thermal resistance, high tensile strength, an
16、d good toughness. Thanks to their small size, large specific surface area and high specific activity, nanoparticles are unique fillers yielding totally different effects and improved physical properties compared to conventional fillers with sizes in the millimeter range. In this study, nano-silica was employed to modify the strength, ductility and rigidity properties of epoxy resin. Compared to the methods of using nano-SiO2 which need surface pretreatment by the effect of silane co
