【作者】 范大鹏；

【导师】 孟令辉；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2013， 博士

【摘要】 碳纤维具有高比强度、高比模量的特点，是制备高性能树脂基复合材料最常用的增强体材料之一。未经处理的碳纤维表面上缺少极性基团及具有化学活性的官能团，其表面呈现惰性无法与基体树脂形成牢固的界面结合，鉴于此碳纤维的表面改性一直受到人们的高度关注。本文尝试在高温高压的超临界流体、亚临界流体中开展对碳纤维表面的清洗和氧化研究工作，为碳纤维的表面改性处理提供新的方法和手段。采用超临界水、超临界丙酮和亚临界条件下的KOH碱液作为介质，对碳纤维表面浆料进行了清洗的实验研究。实验结果显示，超临界水处理可以显著地去除掉碳纤维表面残余的环氧浆料。X射线衍射（XRD）和Raman光谱分析表明，超临界水处理对碳纤维的本体和近表面结构没有显著的影响，碳纤维的单丝拉伸强度平均下降仅2.2%。经超临界水清洗后，碳纤维复合材料的界面剪切强度（IFSS）提高了约17.6%。超临界丙酮和亚临界碱液对碳纤维的表面也具有较好的清洗效果，超临界丙酮清洗适用于去除掉碳纤维表面上的环氧浆料，亚临界碱液清洗则更适用于清洗掉碳纤维表面上的含硅上的污染物。单丝拉伸测试结果则表明，超临界丙酮清洗和亚临界碱液清洗后碳纤维的单丝拉伸强度与通常使用的丙酮抽提方法的数据基本相当。本文分别选用了几种不同类型的氧化剂在超临界和亚临界流体中开展了碳纤维表面的氧化实验研究。在亚临界水体系中以H₂O₂作为氧化剂对碳纤维进行氧化处理，碳纤维表面上的羟基、羧基、酯键和醚键的数量均有小幅的增加。单丝拉伸测试结果表明，该氧化体系造成碳纤维的强度损失约为2.6³.2%，扫描电镜（SEM）观察显示氧化未对纤维表面形貌造成严重影响。在亚临界水体系中以KMnO₄作为氧化剂对碳纤维进行氧化处理，XPS分析数据表明，处理后碳纤维表面上氧元素的含量达到16.0%，高度氧化时碳纤维表面上生成的基团主要以羧基和酯键为主。处理后碳纤维的强度损失平均为3.6%。动态接触角（DCA）测试表明，KMnO₄/亚临界水体系氧化处理后碳纤维的表面能有很大幅度的提高。SEM观察显示，该体系处理会对碳纤维的表面形貌造成显著的影响。为了有效减缓KMnO₄/亚临界水体系处理对碳纤维表面的损害，并且对氧化在碳纤维表面上产生的基团进行控制，将Br₂引入到KMnO₄/亚临界水氧化体系中对碳纤维进行氧化处理。实验结果表明，经Br₂/KMnO₄/亚临界水氧化后碳纤维的氧化效果仍然较好，但高度氧化时碳纤维表面上生成的基团主要以羟基和醚键为主。SEM观察、单丝强度测试和DCA测试的结果均表明，Br₂的引入确实能够在对纤维氧化的同时，对碳纤维的表面起到一定的保护的作用。在超临界Br₂膨胀的浓硫酸体系中对碳纤维进行了氧化处理。XPS分析表明，Br₂/浓硫酸体系对碳纤维表面的氧化处理具有较好的氧化效果，氧化后碳纤维表面上氧元素的含量提高了约10%，碳纤维表面上增加的含氧基团以羟基和醚键为主。DCA测试的结果表明，Br₂/浓硫酸体系处理后碳纤维表面能提高了约14%。该体系造成碳纤维的强度损失较大，约为3.9⁴.5%，碳纤维的表面形貌也会发生较大的变化。体系中Br₂的用量会对氧化程度有一定的影响，适量添加可对碳纤维的表面起到一定保护作用。为了验证与Br同族的卤素Cl是否也能在氧化体系中起到控制氧化损伤以及改变氧化产物基团种类的作用，本文进行了在浓硫酸体系中以KClO3作为主要氧化剂的氧化处理。XPS分析表明，该体系对碳纤维表面的氧化效果较好，处理后氧元素的含量提高了约11%，碳纤维表面上包括羟基、羧基、酯键和醚键在内的含氧基团均有所增加。碳纤维的强度损失约为1.2³.5%。DCA测试表明，采用该体系对碳纤维表面张力非极性分量造成的损害较小。在此基础上，本文针对碳纤维表面氧化的机制进行讨论，将碳纤维表面的氧化过程分为无定形结构的氧化和完整石墨片层边缘的氧化两部分，并且给出了完整石墨片层氧化的特点：首先，完整石墨片层边缘在氧化时会失去表面电荷而被活化；其次，完整石墨片层边缘上羧基和酯键的生成只有通过碳原子的脱除才能够深入的进行；再者，完整石墨片层边缘上含氧官能团的生成会导致石墨片层边缘的扭曲，使高度氧化的石墨片层因不能紧密堆垛而易于被剥离；最后，完整石墨片层边缘的氧化过程伴随着石墨片层电子的迁移，因此在氧化时碳纤维表面对亲电取代反应的活性有所增加。更多还原

【Abstract】 Carbon fibers combine exceptional mechanical properties and low weight, actingas ideal reinforcements for polymer matrix composite materials. The performance ofthese composites depends largely on the quality of the matrix–reinforcementinterface, which determines the way loads can be transferred from the polymer tothe fiber. It has long been recognized that carbon fiber is essentially graphitic innature, when untreated and unsized, and therefore possesses a chemically inertsurface.In this paper, PAN-baded carbon fibers were cleaned and oxidated at hightemperature and presure. The results of XPS indicate that residual layers on thesurfaces of carbon fibers can be thoroughly removed by supercritical water at693Kfor less than9min. The single filament strength of treated fibers decreases slightly.But the results of XRD and Raman measurement suggest that there was noexcessive destruction taken placed in this cleaning procedure.Experimental results also reveal that the method using supercritical acetone orsubcritical potassium hydroxide aqueous solution act as the processing mediumshows a better cleaning effect compared to the traditional method, Soxhletextraction with acetone. The method using supercritical acetone is more appropriateto wipe off the oxygenated contaminants on carbon fibers’ surfaces and causes arelatively smaller damage to the bulk strength of each carbon fiber. As far as treatingmethod using the subcritical alkali aqueous solution, it can thoroughly removesilicious contaminants on the surfaces of treated fibers.After oxidation by H₂O₂/subcrtical water systems, oxygen content of the treatedfibers enlarged about5%. The monofilament tensile strength decreased about2.6³.1%. The results of SEM observations indicate that oxidation reaction therewas no significant effect on the surface appearance of the treated carbon fibers.After oxidation by KMnO₄/subcrtical water systems, oxygen content of thetreated fibers increased to16.0%, meanwhile, the grooves on the surfaces of thecarbon fibers were deepened gradually after treatments. The results of dynamiccontact angle measurements suggest that an obvious increase of the carbon fiber’ssurface tension is mainly because of the enlargement of its polar component. Aftertreated with increasing amounts of oxidants, the monofilament tensile strength decreased about3.6%.To reduce the damages of the oxiadation treatments and control the generationgounps, Br₂was mixed into these systems. It shows that the oxidation can alsoincrease the oxygen content on fiber surfaces, but the generating group is hydroxyrather than carboxyl. Scanning electron microscope was used to follow the surfacetopography of the fibers. It reveals that the grooves on the surfaces of the oxidatedfibers were deepened gradually for both oxidation systems.After oxidation by Br₂/concentrated sulfuric acid, oxygen content of the treatedfibers increased about10%. DCA measurement show that carbon fiber’s surfacetension increased about14%, and The monofilament tensile strength decreasedabout3.9⁴.5%. And the results of SEM observations indicate that oxidationreaction has a significant effect on the surface appearance of treated carbon fibers.In order to follow how the effect of Cl2compared with Br₂in the oxidationsystems, the carbon fibers were oxidized with KClO3/H2SO4systems. The XPSresults show that oxygen functional groups on the surfaces of carbon fibers increaseby about11%after treated, and the main of them are hydroxys and carboxyls. Theresults of monofilament tensile tests verify that the strength loss of the treated fiberswere about1.2³.5%.A discusion of the mechanism of carbon fibers is given in this paper. It indicates:decarburizing step takes place before the formation of carbonyl and carboxyl groups,so mass loss in the highly oxidizing process of carbon fiber is inevitable; because ofsteric hindrance, the formation of the carbonyl and carboxyl groups leads togenerally warping graphite layers; the generation of lactone bond is preferred to thegeneration of carboxyl group in the oxidation process of carbon fibers.更多还原