【作者】 徐淑杰；

【导师】 钱家盛；

【作者基本信息】 安徽大学 ， 高分子化学与物理， 2012， 硕士

【摘要】 纳米氮化硅(Si3N4)是一种性能优异的陶瓷材料被广泛应用于聚合物基纳米复合材料的制备。但纳米Si3N4陶瓷粉体具有高表面能、高比表面积在使用过程中很容易团聚,导致其在聚合物基体中很难达到纳米级的分散。使用改性剂对纳米Si3N4进行表面修饰能够有效地改善聚合物基体和纳米粒子之间的相容性,提高粒子的分散性。利用性能优异的无机纳米粒子开发新型特殊性能的聚合物基纳米复合材料国内外已有大量文献报道,而对纳米材料如何影响聚合物结晶行为的研究尚不完善。故本文针对纳米Si3N4的表面改性、纳米Si3N4在聚合物基体中的分散、聚合物基体的结晶行为以及纳米粒子对基体结晶过程的影响进行了研究。1、根据聚合物的化学结构特征,参照本实验室的工作经验,采用小分子改性剂KH570对纳米Si3N4进行表面修饰,以便提高其与聚合物基体的相容性,阻碍团聚的发生。通过红外(IR)、热重分析仪(TGA)、透射电镜(TEM)、沉降实验等手段对改性后的纳米Si3N4进行表征,结果表明改性剂KH570已成功键接在纳米Si3N4上,最佳百分用量为Si3N4用量的33wt%,键接方式主要为化学键键接,化学包覆率为13.05wt%,改性Si3N4在聚合物基体中的分散达到了纳米尺度上的分散。2、采用溶液共混法制备了聚己内酯PCL/纳米Si3N4复合材料,利用差示扫描量热分析仪(DSC)、偏光显微镜(POM)、 X射线衍射(XRD)和透射电镜(TEM)研究了PCL和PCL/Si3N4纳米复合体系的结晶行为,并探讨了降温速率、Si3N4的含量、Si3N4的表面性质等因素对体系结晶过程的影响。主要发现纳米Si3N4具有成核作用,可以减弱聚合物PCL对降温速率的依赖,但不会改变PCL的晶体结构；随其含量的增加聚合物的结晶温度Tc和结晶开始温度Tstart也提高,并在5wt%时出现最大值；PCL44℃等温结晶、PCL48℃等温结晶以及PCL/Si3N4复合材料48℃等温结晶球晶生长速率分别为16.46×lO-3μm/s、3.87×lO-3μm/s,且球晶生长速率越慢,球晶半径却越大。3、使用DSC法测试了PEO和PEO/Si3N4纳米复合物的结晶曲线和熔融曲线并总结、阐述了结晶温度Tc和熔融温度Tm及单位质量吸收的热量△H随分子量变化的关系,又进一步将数据处理得到了相对结晶度Xt与结晶时间t的变化曲线并利用Avrami方程对曲线进行了模拟。对POM照片进行定性观察和定量分析,绘制了球晶半径对结晶时间的曲线和晶核密度对结晶时间的曲线,并解释了它们的变化与分子量的关系。最后使用TEM和XRD分析了聚合物的晶体结构,发现PEO的晶型与分子量无关,但低分子量的PEO结晶能力更好,晶体更完善。更多还原

【Abstract】 Nano-silicon nitride (SisN4) powder is a high performance structural ceramic material and it has been widely used in the preparation of polymer nanocomposites. However, the high surface energy and large specific surface area of nano-Si3N4easily leads to aggregation when it is used in the materials. So the powder can not reach nanometer scale dispersion in the polymer matrix. By adding modifier, the compatibility between polymer matrix and nano-particles as well as the dispersion of nano-particles can be improved effectively. A lot of literatures have described the methods of developing novel polymer-based nanocomposites with special properties using high performance inorganic nano-particles, but it is not clearly explained on how the nano-particles affecting the crystallization behavior of semi-crystalline polymer matrix. In this paper, the surface modification of nano-SisN4, the dispersion behavior of nano-Si3N4in the semi-crystalline polymer matrix, the crystallization behavior of the polymer matrix and the impact of nano-Si3N4on the crystallization process of the polymer matrix are deeply investigated.1. According to the chemical structure characteristics of the crystalline polymer and the experience of our laboratory, low molecular modification agent KH570is used to modify the surface of nano-Si3N4and improve the compatibility between nano-Si3N4and the polymer matrix as well as to prevent the happening of the aggregation. The structure of modified nano-Si3N4is investigated by IR,TGA, TEM and settlement experiment, The results show that modifier KH570is already successful bonded on the surface of nano-Si3N4, the best percentage is33wt%and the chemical coating rate is13.05wt%, the modified nano-Si3N4has reached nanometer scale dispersion in the polymer matrix.2. The composites of PCL/nano-Si3N4and PEO/nano-Si3N4were prepared by solution blending. The crystallization behavior of polycaprolactone (PCL) and PCL/Si3N4nanocomposites is measured by DSC, polarizing microscope (POM), X-ray diffraction (XRD) and transmission electron microscopy (TEM), and how the cooling rate, the content of nano-Si3N4, the surface properties of nano-Si3N4and other factors’effect on the crystallization process are explained too. The results show that nano-Si3N4has nucleation effect and can reduce the dependence of the polymer on the cooling rate, while the crystal structure of PCL is not changed during the process. With the increasing content of nano-Si3N4, the crystallization temperature Tc and the initial crystallization temperature Tstart of polymer matrix are improved when the content of nano-Si3N4reaches5wt%, Tc and Tstart can reach maximum. The spherocrystal growth rate of PCL are16.46×10-3μm/s and12.83×10-μm/s when the isothermal crystallize are at44℃and48℃, respectively, while the spherocrystal growth rate of PCL/Si3N4composite is3.87×10-3μm/s when the isothermal crystallize is at48℃. The slower the spherulite growth rate, the bigger the spherocrystal radius is.3. The crystallization curve and the molten curve of PEO and PEO/Si3N4nanocomposites are measured by DSC. The changing of the crystallization temperature Tc and melting temperature Tm and AH with different molecular weight and are summarized. Further data processing is made to get the curve of the relative crystallinity Xt with crystallization time and the data is simulated by using Avrami equation. The plots of the spherocrystal radius to the crystalline time and the crystalline nucleation density to the crystalline time are investigated by analyzing the PEO photos. The changing of the spherocrystal radius and the crystalline nucleation density with different molecular weight are explained. The crystal structure of the polymers is studied by using TEM and XRD, and the results show that the crystal structure of PEO is independent on the molecular weight. But the PEO with low molecular weight has a better crystallinity and more perfect crystal structure.更多还原