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The Design Of Extensional Rheometer And Extension Induced Crystallization

Posted on:2011-05-19Degree:MasterType:Thesis
Country:ChinaCandidate:T Z YanFull Text:PDF
GTID:2121360308455561Subject:Synchrotron radiation and its application
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Flow-induced crystallization is the core problems in polymer processing and an important project in polymer science. In the past several decades, polymer processing scientists have drawn the following three important results:Flow can enhance polymer crystallization dynamics and change crystal morphology from spheres to shish-kebab. Second, flow enhances polymer crystallization dynamics mainly by enhancing nucleation process. Third, molecular weight and molecular weight distribution have an important impact on polymer crystallization. It is believed that high molecular weight part play a central role in the formation of flow-induced structure and enhancing crystallization dynamics.However, quantitatively study on flow-induced crystallization is few, which is the main problems preventing our way to fully understand flow-induced crystallization. Based on the previous researches on flow-induced crystallization, we draw a conclusion that it is necessary to introduce rheology into flow-induced crystallization to fully elucidate the mechanisms of flow-induced crystallization. The research mainly include the following three parts:The first part describes the design, fabrication and testing of the extensional rheometer. Based on SER, the modern commercial extensional rheometer and the extensional equipment used for studying extensional rheology of polymers in the history, we choose motor and torque sensor and design heating cabin based on the sample we choose, and the availability of combination with synchrotron radiation. With the help of mechanical design and software control, high-speed motor, high-level torque transducer and the extensional part were combined together to gain an extensional rheometer. Finally, adjustments of mechanics, temperature controlling, and motor programs for many times come out of an extensional rheometer. Tests demonstrate that the instrument is satisfactory for our rheological experiments.The second part deals with studying the critical strain for shish formation with our home-made extensional rheometer. Based on the newly research results on extensional rheology of polymers, we quantitatively studied mechanisms of shish-kebab formation in HDPE polymer melts. And we found that the mechanisms of shish-kebab is not coil-stretch mechanism but stretching of chain segments between entanglement points.
Keywords/Search Tags:flow-induced crystallization extensional flow, polymer processing, extensional rheometer, shish-kebab, HDPE, polymer melt extension
PDF Full Text Request
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