【作者】 杨建；

【导师】 张立群；

【作者基本信息】 北京化工大学 ， 材料加工工程， 2008， 博士

【摘要】 石墨是一种层状材料,具有优良的润滑性能,在剥离的状态下拥有非常高的形状系数,石墨片层是比强度最高的材料之一,而且拥有独特的功能特性,例如优异的导电性和导热性等。与碳纳米管相比,石墨的价格要低很多。本文考察了石墨粒径对丁腈橡胶性能的影响,然后采用乳液共混的方法成功制备了石墨/橡胶纳米复合材料,并对其性能作了系统的研究。在论文的第一部分中,选用了四种商品化的不同粒径的石墨粉,采用熔体共混法分别将其直接加入丁腈橡胶中,填充变量均为20、40、60份,主要研究了石墨粒径及分散对丁腈橡胶力学性能及摩擦磨损性能的影响。研究表明,直接的熔体共混法制备的石墨/丁腈橡胶复合材料中,膨胀石墨的疏松结构未能在双辊的强烈剪切力作用下分散为均匀的细小颗粒,而是有少量颗粒分散到较小的尺度,但大部分的分散相片层的直径仍然在100μm左右,厚度约几个微米。超细石墨粒径小,对橡胶力学性能的补强效果好。在相同的填充份数下,超细石墨填充的丁腈橡胶硫化胶是四种胶料中300%定伸应力和拉伸强度最高的,而且扯断永久变形小。增加石墨的用量可以提高丁腈橡胶硫化胶的摩擦学性能。在60 phr填充量下,大粒径分散的石墨(EG)填充的丁腈橡胶其摩擦系数相对要低,而小粒径分散的石墨(超细石墨)填充的丁腈橡胶则具有最小的磨损率。在应用石墨作为改性填料时,应使用小粒径石墨,可以在保持橡胶机械性能的同时提高其摩擦学性能。在论文的第二部分,为制备石墨/丁腈橡胶纳米复合材料,首先采用超声波粉碎处理膨胀石墨来制备石墨纳米薄片,然后对直接共混、通过低聚物液体丁腈橡胶预处理石墨、以丙酮作为溶剂进行溶液共混、采用不同表面活性剂进行乳液共混的方法进行了对比研究。结果表明,首次提出的乳液共混法(LCM法)可成功地制备石墨/丁腈橡胶纳米复合材料。电镜观察及XRD分析结果说明,采用十二烷基磺酸钠稳定纳米石墨水悬浮液,并与丁腈橡胶乳胶共混共沉制备的石墨/丁腈橡胶纳米复合材料中,石墨分散均匀,片层的聚集体尺寸更小,达到了纳米片层的尺度,而且同时存在橡胶大分子插层、表面活性剂插层以及未插层的多种石墨分散结构。通过力学性能、动态力学性能、功能性能的测试,发现石墨/丁腈橡胶纳米复合材料具有大幅提高的力学性能,在10 phr的石墨用量内,纳米复合材料的硬度、定伸应力及拉伸强度均随着石墨用量的增加而明显提高,断裂伸长率则有所下降;纳米石墨的加入对复合材料的动态储能模量有明显的增强效果,特别是在橡胶态下,纳米复合材料的动态模量比纯胶大幅度提高,而且随着石墨用量的增加,纳米复合材料的玻璃化转变温度明显向高温方向移动;复合材料的摩擦系数降低,磨损性能大大提高;复合材料还具有多样的功能特性,如优异的耐磨性能、优异的气体阻隔性能、一定的导电性能及导热性能等。论文的第三部分中,通过对石墨/丁腈橡胶及石墨/丁苯橡胶纳米复合材料硫化特征的研究,发现其特殊的自发硫化行为,即不需要其它的硫化剂就可以在一定的温度下硫化交联。自硫化需要活化能,对温度有一定的依赖性。平衡溶胀实验的结果、交联密度的测定、自硫化前后橡胶材料玻璃化转变温度的变化,则进一步证实了自硫化的存在。通过ESR分析以及对硫化曲线特征的总结,可以初步认为自硫化过程的机理为纳米石墨片层上的自由基引发交联,而其引发效率与石墨片层的分散密切相关。自硫化行为的最大特点是高度强化纳米复合材料的界面。本文的最后通过LCM方法制备了纳米石墨/羧基丁腈橡胶及纳米石墨/丙烯酸酯橡胶复合材料,并对其结构与性能作了初步的研究。扫描电镜观察发现石墨在这两种橡胶基体中的分散都很均匀,石墨片层的直径较大、而厚度则在纳米级范围。力学性能测试表明,与石墨/丁腈橡胶纳米复合材料相似,随着纳米石墨用量的增加(羧基丁腈橡胶中:0～20 phr;丙烯酸酯橡胶中:0～10 phr),复合材料的力学性能逐渐提高,其中以定伸应力的提高最为显著。更多还原

【Abstract】 Graphite is a layered material possessing excellent lubrication property and high aspect ratio in an exfoliated state, and it is also one of the strongest materials per unit weight with unique functional properties, e.g. good electrical and thermal conductivities. In addition, graphite is very cheap compared to carbon nanotubes. In this paper, the influence of graphite particles size on the properties of NBR was firstly investigated, graphite/rubber nanocomposites were successfully fabricated through latex compounding technology, and the properties of graphite/rubber nanocomposites were systematically studied, mainly using NBR as matrix material.Firstly, four graphite powder fillers with different form and size were mixed through melt compounding with NBR at 20, 40 and 60phr of the filler loadings, and the obtained compounds were characterized by SEM, tensile test, friction and wear test. Through the SEM observation, it was found that the expanded graphite could not be broken down to small particles uniformly when blended with rubber on the twin-roller. In the tensile test, the graphite with the smallest size possessed the best reinforcement ability as expected. The tribological properties of the rubber were improved when adding more graphite. The largest graphite particles imparted the lowest friction coefficient of the composites among four fillers, but the sub-micrometer graphite provided the best wear property to NBR.Secondly, a facile latex approach has been adopted to finely incorporate graphite nanosheets into rubber matrix and achieve high performance elastomeric nanocomposites with both excellent mechanical properties and versatile functional properties. Scanning electron microscope, transmission electron microscope and X-ray diffraction experiments show that the nanostructures of the obtained nanocomposites are higher extent of exfoliation and intercalation of graphite in the NBR matrix. Mechanical and dynamic mechanical tests demonstrate that The NBR nanocomposites possess greatly increased modulus and strength, and desirable strong interface. Moreover, The NBR nanocomposites possess greatly improved wear resistance, better gas barrier property, and good electrical/thermal conductivity. These versatile functional properties make NBR/EG nanocomposites a new class of promising advanced materials.The unexpected self-crosslinking of graphite/elastomeric nanocomposites was discovered and proved through oscillating disc rheometer and equilibrium swelling experiment. Investigated by various polymer types, X-ray photoelectron spectroscopy, electron spin resonance and Fourier transform infrared spectroscopy, a radical initiation mechanism was put forward to explain the self crosslinking reaction.In the final part, graphite/xNBR and graphite/ACM composites were prepared via LCM and their structure and the mechanical properties were studied.更多还原