用于复合泡沫塑料的中空热塑性微球的几何和力学表征
Geometrical and Mechanical Characterisation of Hollow Thermoplastic Microspheres for Syntactic Foam Applications
摘要：
最近，中空热塑性微球，如由Nouryon制造的Expancel，已经成为用于聚合物基复合材料的创新填充材料。所制备的全聚合物复合泡沫塑料具有优异的损伤容限性能、强的大应变恢复能力和良好的能量耗散特性。尽管在各种行业和应用中发现越来越多的使用，包括在涂料，薄膜，密封剂，包装，微流体复合材料，医疗超声和多孔复合材料中，但Expancel微球的统计几何信息几乎完全缺失。此外，其机械性能尚未报道。在这项工作中，我们使用X射线计算机断层成像，聚焦离子束和电子显微镜的两类Expancel热塑性微球的几何量。我们还观察了微球的空间分布内的聚乙烯基复合泡沫塑料。我们发现，在这两类微球的体积加权多分散壳直径遵循正态分布。有趣的是，没有观察到壳壁厚度的多分散性，特别是壳厚度与壳直径不相关。我们采用测得的几何信息，在小应变制度的分析微机械技术，以确定，第一次，估计的杨氏模量和泊松比的微球壳材料。我们的研究结果有助于潜在的未来改进的设计和制造的复合泡沫塑料，采用热塑性微球。考虑到利用热塑性微球的领域的广度，我们预计我们的结果以及所使用的方法将在未来材料研究的更广泛范围内使用。
英文摘要：
Recently, hollow thermoplastic microspheres, such as Expancel made by Nouryon, have emerged as an innovative filler material for use in polymer-matrix composites. The resulting all-polymer syntactic foam takes on excellent damage tolerance properties, strong recoverability under large strains, and favourable energy dissipation characteristics. Despite finding increasing usage in various industries and applications, including in coatings, films, sealants, packaging, composites for microfluidics, medical ultrasonics and cementious composites, there is a near-complete absence of statistical geometrical information for Expancel microspheres. Further, their mechanical properties have not yet been reported. In this work we characterise the geometrical quantities of two classes of Expancel thermoplastic microspheres using X-ray computed tomography, focused ion beam and electron microscopy. We also observe the spatial distribution of microspheres within a polyurethane-matrix syntactic foam. We show that the volume-weighted polydisperse shell diameter in both classes of microsphere follows a normal distribution. Interestingly, polydispersity of the shell wall thickness is not observed and in particular the shell thickness is not correlated to the shell diameter. We employ the measured geometrical information in analytical micromechanical techniques in the small strain regime to determine, for the first time, estimates of the Young's modulus and Poisson's ratio of the microsphere shell material. Our results contribute to potential future improvements in the design and fabrication of syntactic foams that employ thermoplastic microspheres. Given the breadth of fields which utilise thermoplastic microspheres, we anticipate that our results, together with the methods used, will be of use in a much broader context in future materials research.
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