层状硅酸盐/橡胶纳米复合材料的结构与性能研究

【作者】 张惠峰；

【导师】 张立群；

【作者基本信息】 北京化工大学 ， 材料学， 2004， 博士

【摘要】 本论文基于张立群教授等提出的“粘土晶层悬浮液/橡胶乳液互穿纳米复合技术”,制备了一系列层状硅酸盐/橡胶纳米复合材料(橡胶基体主要包括丁苯橡胶、天然橡胶和丁腈橡胶,层状硅酸盐包括蒙脱土和累托石),详细研究了该类橡胶纳米复合材料的结构与性能特点,并分析了二者之间的关系,以期为该材料在工业产品中的应用提供理论指导。透射电子显微镜和X-射线衍射分析表明,乳液法制备的层状硅酸盐/橡胶纳米复合材料的结构为“隔离型”结构,其分散相包括部分完全剥离的单片层,以及层间无高分子插入的纳米晶束;这种独特的结构赋予了该类材料与传统炭黑,白炭黑以及微米粘土填充橡胶体系不同的性能特点,在较小用量下具有较高的物机性能,尤其是硬度、定伸应力和撕裂强度。用动态机械热分析(DMTA)和橡胶加工分析仪(RPA)对该材料动态力学性能的研究表明,具有较大长径比的层状硅酸盐与其他填料相比,对橡胶分子链的限制作用更强,因此橡胶纳米复合材料在玻璃化转变区的内耗峰较低,而在后期的内耗却又较高;层状硅酸盐的引入可以显著提高橡胶的弹性模量。层状硅酸盐在小用量下可以提高SBR和NBR的磨耗性能,用量增加到一定值后,由于层状硅酸盐二次聚集体的形成而导致应力集中,对磨耗性能产生负面影响,这不同于炭黑体系中磨耗量随炭黑用量增加而逐渐下降的规律;天然橡胶体系中填料的加入会引起磨耗量的增加,填料种类和用量对磨耗量的影响规律与SBR和NBR体系一致。RPA和孟山都毛细管流变仪对材料流变性能的研究表明,与炭黑填充胶料相比,层状硅酸盐/橡胶纳米复合材料具有较强的填料网络结构;混炼胶粘度稍高,尺寸稳定性好,具有良好的加工性能,为生产高质量的产品提供了保证。优异的气密性是层状硅酸盐/橡胶纳米复合材料的突出特点之一,本论文考察了多种橡胶体系纳米复合材料以及丁苯橡胶中多种填充体系的气体阻隔性,借助TEM和XRD确定了层状硅酸盐在橡胶中的形状系数(宽厚比);在合理假设的基础上,经过严格的数学推导得到了填料对橡胶气体阻隔性贡献的理<WP=5>论计算模型,并与实验值进行了拟合,该模型与Nielsen模型相比,可以更好地解释实验现象。材料的自由体积与气体渗透性能密切相关,利用正电子湮没寿命研究了丁苯橡胶多种填充体系的自由体积空穴平均大小、浓度以及自由体积分数与填料种类和用量之间的关系,填料的种类和用量对橡胶自由体积空穴的平均大小影响不大,而对自由体积的浓度影响较大;橡胶的自由体积浓度随层状硅酸盐用量增加变化较小,而随炭黑用量增加逐渐降低;随着温度的升高,分子链运动能力增大,材料的自由体积增加;虽然炭黑填充体系可以较好的用自由体积理论(D=Aexp(-B/Fv))来描述气体扩散系数与自由体积之间的关系,但层状硅酸盐/橡胶纳米复合材料不符合该理论,主要原因在于层状硅酸盐对气体阻隔性能的提高归因于高的形状系数延长了气体在橡胶的扩散路径,说明填料的阻隔效应要加以考虑。层状硅酸盐/橡胶纳米复合材料的热稳定性、老化性能以及阻燃性能的研究结果表明,该类橡胶纳米复合材料具有较高的热稳定性;蒙脱土/橡胶纳米复合材料的热氧老化、臭氧老化优于相应的纯橡胶和相同用量的炭黑和白炭黑硫化胶;在实验范围内,蒙脱土/NR纳米复合材料的抗紫外老化性能随着蒙脱土用量的增加而变好,而炭黑体系中填料用量的影响不明显。采用锥形量热仪、氧指数、水平和垂直燃烧等研究了蒙脱土/丁苯橡胶纳米复合材料的阻燃性能,该材料的热释放速率和质量损失速率均大大降低,但氧指数提高不大,与氢氧化镁并用后,可以得到兼具良好力学性能和阻燃性能的纳米复合材料;采用乳液法制备的高填充量蒙脱土/丁苯橡胶复合材料是一种微纳米复合材料,具有较好的阻燃性能,特别是与少量白炭黑配合后,明显提高了氧指数和水平燃烧级别。更多还原

【Abstract】 Recently layered silicate/polymer nanocomposites have attracted many researchers’ interests. Consequently, it is of great important to well understand their structures and properties in order to obtain information for their applications in industry. Several layered silicate/rubber nanocomposites are prepared by directly co-coagulating the rubber latex and layered silicate aqueous suspension (rubbers including styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR) and natural rubber (NR); layered silicate including montomorillonite(MMT) and rectorite). X-ray Diffraction (XRD) patterns and Transmission Electron Microscopy (TEM) micrographs show that the nanocomposites by this method are a novel “separated” layered silicate/rubber nanocomposites, in which the rubber molecules separate the layered silicate particles into either individual sheet, or just nano-scale silicate sheet aggregates without the intercalation of rubber molecules. Compared with carbon black or silica filled rubber, this kind of layered silicate/rubber namocomposites exhibit excellent mechanical properties, such as high hardness, high stress at a certain strain and high tear strength. The results of DMTA reveal that the nanocomposites represent a lower tanδ peak value within the zone of glass transition temperature (Tg), while a higher tanδvalue at high temperature. The elastic modulus of the nanocomposites is highest compared to the unfilled rubber and carbon black filler rubber. These results are in consistent with the results from Rubber Processing Analysis (RPA). The processing properties of MMT/SBR nanocomposite are investigated by means of Monsanto Rheometer and RPA. At the same time, these results are compared with those of carbon black filled SBR. The results indicate that the rheology of these two composites is similar, however, layered silicate/SBR <WP=7>nanocomposites exhibit stronger filler network and higher viscosity compared to those of carbon black/SBR composites. Moreover, the extruder surface of layered silicate/SBR nanocomposite is more smooth than that of SBR filled by carbon black. All these results reveal that the nanocomposites have good processing properties. The permeabilities of several layered silicate/rubber nanocomposites and carbon black filled rubber are measured. The aspect ratios (area/thickness) of these nanocomposites are obtained by use of the TEM and XRD. Based on reasonable hypothesis, a theoretical mode is established to predict the reduction of permeability in a filled rubber according to the content and the structure size of the filler. Compared with the Nielsen model this model is more suitable to describe the experimental data. The factors of the permeability in filled rubber are discussed according to the theoretical mode. Positron annihilation lifetime spectroscopy (PALS) has been used to study the available free volume hole size(o-Ps lifetime) and concentration (o-Ps intensity) of MMT/SBR nanocomposites and SBR filled with carbon black. The variation of filler type and the filler content have little effect on the o-Ps lifetime, but alter the o-Ps intensity in the filled rubber. With the amount of filler increasing, the o-Ps intensity decreases in carbon black filled SBR, but increases followed with decrease in MMT/SBR nanocompoistes. This can be attributed to their different interface with SBR. Although a good correlation is found between diffusivity (D) and free volume fraction(Fv) based on D=Aexp(-B/Fv) according to free volume theory in carbon black/SBR, a non-linear relationship is observed in MMT/SBR. The reason is that the addition of impermeable fillers (such as MMT) may not significantly modify the available free volume but will cause a significant decrease in the diffusivity due to tortuosity effects. The effect of temperature on the free volume and permeability are also studied. Although the free volume and the permeability of filled SBR increase obviously with temperature increasing, the activation energies calculated according to the Arrhenius’ law are almost th更多还原