塑膠熔融體暫態剪切黏度的流變學理論模擬

Rheological Theory and Modeling of Transient Shear Viscosity of Plastic Melts

林冠甫(Kuan-Fu Lin)

指導教授 ： 林國賡

淡江大學/工學院/化學工程與材料工程學系碩士班/碩士(2018年)

https://doi.org/10.6846/TKU.2018.00332

摘要

本研究主旨在於分析高分子材料於熔融狀態之暫態剪切流動行為，探討兩次剪切間隔時間、剪率、溫度對材料暫態黏度（或應力增長）之影響，並且嘗試量化黏彈性流體在啟動剪切之後，其分子結構恢復所需時間。本研究所選用之材料為聚碳酸酯，其為一常見的熱塑型工程塑膠，具優良耐衝擊性，並常應用於樹酯鏡片、燈罩等光學相關產品。本研究首先利用平板式流變儀進行暫態剪切流動實驗，取得暫態黏度數據，其次應用流變學模式(White-Metzner and the convected Jeffrey model)來分析瞬間啟動剪切之流變行為，並且聚焦在觀察啟動流動瞬間的應力過衝現象。由結果得知，於第一次啟動剪切，因為高分子鏈之不定向排列，其應力過衝會很明顯，而且當剪切率越高，高分子鏈的彈性效應也較顯著，應力過衝數值亦會越高。在進行第二次剪切實驗，其與第一次剪切結束不同間隔時間，高分子鏈產生不同程度的重新排列，時間隔越久分子鏈恢復就越多，遂造成其應力過衝程度較趨近於第一次剪切應力過衝數值。再者，實驗溫度是影響高分子材料黏彈性之重要因素，本研究發現於相同剪率下，溫度較低其材料彈性效應較強，所得的應力過衝現象也較顯著。

關鍵字

暫態黏度 ； 應力過衝 ； 流變性質 ； 聚碳酸酯 ； 高分子黏彈性

並列摘要

The main purpose of this research is to analyze the transient shear flow behavior of polymer materials in the molten state. The effects of two shear intervals, shear rate, and temperature on the transient viscosity (or stress increase) of the material were investigated, and attempts were made to quantify the time required for the recovery of the molecular structure of the viscoelastic fluid between two consecutive instant shearing. The material selected for this study is polycarbonate, which is a common thermoplastic engineering plastic with highimpact resistance. In this study, the plate-type rheometer was used to obtain thetransient viscosity data. BoththeWhite-Metzner and the convected Jeffrey models were used to analyze the rheologyof the instantshear flow, focusing on tracking the stress overshoot accompanying thestart-up of the shearing flow. From the results, it can be seen that when the shear flow starting for the first time, the stress overshoot could be very apparent because the polymer chains are randomly coiled, and the higher the shear rates, the more elastic the polymer chainsare; thus the extent of the overshoot becomes higher.Bytheimmediateconsecutiveshearing, the polymer chains couldberecoiled to variantextentsinaccordancewiththetimeintervalsfrom the first shearing. The longer the time intervals, the more the molecular chainsare recovered, and thusthe stress is growing up more obviously. Ultimately, itisapproaching the stress overshoot for the first-time shearing. It is known that the temperature is an important factor influencing the viscoelastic properties forthe polymer materials. In this study, it was found that under the same shear rate, the material at lower temperature possessed stronger elasticity, and the resulting stress overshoot at the start-up of shear flow wasmore significant.

並列關鍵字

Transient viscosity ； stress overshoot ； rheology ； polycarbonate ； polymer viscoelastic

參考文獻

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