以超(次)臨界流體技術製備複材及量測CO2膨脹溶液中之擴散係數

Prepartion of Polymer Composite in Sub/Supercritical Fluid and Measurement of Diffusion Coefficients in CO2-Expanded Liquids

林義翔(I-Hsiang Lin)

指導教授 ： 談駿嵩

國立清華大學/工學院/化學工程學系/博士(2009年)

摘要

本研究在以超(次)臨界流體技術製備複材及量測二氧化碳膨脹溶液系統之擴散係數。內容分為四個章節說明，各章節內容摘要分述如下：
第一章 ”緒論”說明超臨界流體的基本物性，並就超臨界流體應用在高分子製程上的特性與有機溶劑經高壓氣體膨脹後的溶液特性做一說明。
第二章介紹以超臨界流體含浸法製備TiO2/PC和TiO2/PET複合材料。當高分子材料置於超臨界流體時，可由調整壓力與溫度來改變高分子被超臨界流體膨脹的程度，並趨使TiO2奈米粒子能被流體挾帶入高分子內。本章探討三種不同機制的含浸方式，其中以當高分子薄膜事先浸泡在含懸浮TiO2奈米粒子的溶液中，然後再通入高壓CO2的含浸方式可以得到較佳之含浸效果，然而所觀察到TiO2的含浸皆發生在高分子的表面上。
第三章利用連續式壓縮流體反溶劑法製備複合材料，其中包含製備TiO2/PS奈米複合粒子、PMMA微粒和PS/PMMA混摻高分子。當將含有懸浮TiO2奈米粒子的高分子溶液經由噴嘴噴入充滿反溶劑之沈澱槽時，溶液中的溶劑會擴散進入反溶劑中而被帶出沈澱槽外，此時PS會因為達到過飽和而在TiO2粒子表面上析出而生成TiO2/PS複合粒子。在改變不同操作變數後，可知當操作溫度為298 K，操作壓力為6.41 MPa，反溶劑液面佔1/4沈澱槽高度，PS濃度為0.72 wt%，PS與TiO2添加比例為8時，可以得到TiO2/PS Core/Shell型態的複合粒子。由於PMMA很容易受CO2的塑化而不易在高壓CO2中生成球狀PMMA微粒，因此本操作在不添加任何穩定劑的前提下進行，以探討不同操作變數下所得到之PMMA微粒型態。由實驗結果可知當操作在溫度為298 K，壓力為6.41 MPa，高分子溶液流速為5 mL/min，CO2流率為2000 mL/min，液相CO2的液面在1/8沈澱槽高度，PMMA高分子溶液濃度小於或等於1 wt%時，可以得到次微米級的PMMA球狀微粒。在製備PS/PMMA混摻高分子時，當操作溫度為298 K，壓力為6.41 MPa，高分子溶液流率為5 mL/min，CO2流率為2000 mL/min，液相CO2的液面在1/4沈澱槽高度以上時，使用高分子溶液濃度在1 wt%以下時，可以得到大多數為次微米級之混摻高分子微粒；使用濃度在2至8 wt%時，可得到微米級與次微米級之微粒。當添加之PS/PMMA比例為9/1，液相CO2的液面在1/2沈澱槽高度，PS分子量為144,000和PMMA分子量為36,000時，可得到主要型態為PS/PMMA Core/Shell的混摻高分子產物。
第四章主要進行溶質在二氧化碳膨脹溶液中之擴散係數量測。在氫化反應中，由於氫氣在有機溶劑中之溶解度不高，氣液間也存在界面質傳阻力，此外液體中的擴散阻力也會對反應速率造成限制。當有機溶劑中加入高壓CO2時，會形成二氧化碳膨脹溶液，除了可增加氫氣在溶液中的溶解度外，也會因溶劑體積膨脹而導致液體密度與黏度的降低，因而減少液相中之擴散阻力。本章節為量測對氯硝基苯在二氧化碳膨脹甲醇溶液與量測苯甲腈在二氧化碳膨脹乙醇溶液中之擴散係數，探討變數包含溶液中之CO2濃度、溫度與壓力等。由實驗結果可知溶質在二氧化碳膨脹溶液中的擴散係數較在純溶液中為高，且隨著溶液中二氧化碳含量的增加而愈有利於溶質的擴散。在固定壓力下，溶質的擴散係數會隨溫度上升而增加；在固定溫度下，溶質的擴散係數會隨溶液壓力的增加而下降。針對不同之擴散系統可建立對應之擴散係數關聯方程式。

關鍵字

超臨界流體 ； 超臨界流體含浸法 ； 壓縮流體反溶劑法 ； 複合材料 ； 二氧化碳膨脹溶液 ； 擴散係數

並列摘要

The preparation of polymer composites using sub/supercritical fluids and the measurement of diffusion coefficients in CO2-expanded liquids are included in this dissertation. There are four chapters, which are organized as follows:
In Chapter 1, the physical properties of supercritical fluids, and the applications of supercritical fluids in polymer processing as well as the characteristic properties of gas-expanded liquids were described.
In Chapter 2, the preparation of TiO2/PC and TiO2/PET composites using supercritical impregnation was investigated. The extent of polymer expansion could be controlled by adjusting the pressure and temperature of supercritical fluids and the impregnation of TiO2 nanoparticles into the polymer matrix with supercritical fluids was therefore achived. Three different mechanisms of impregnation were studied in this chapter, and the optimum way of impregnation was found when the polymer film was immersed in the suspension solution of TiO2 prior to the introduction of compressed CO2 into the solution. However, the impregnation of TiO2 in this study was observed to occur only on the polymer surface.
In Chapter 3, the preparation of polymer composites including TiO2/PS nanocomposites, PMMA particles, and PS/PMMA blending polymers by using continuous PCA method was studied. When the polymer solution with suspended TiO2 was sprayed into an antisolvent environment through a nozzle, the supersaturation of PS was achieved and the precipitation of PS on TiO2 surface occurred. The morphology of TiO2/PS core/shell structure was obtained for a temperature of 298 K, a pressure of 6.41 MPa, a liquid CO2 level in the precipitator of 1/4, a PS concentration of 0.72 wt%, and a PS/TiO2 ratio of 8. Due to the facile adsorption of CO2 in PMMA, spherical PMMA particles were not easily formed in compressed CO2 environment. In this chapter, the preparation of PMMA particles without adding any stabilizers was conducted by adjusting several operating variables, and the spherical PMMA submicron-sized particles were obtained for a temperature of 298 K, a pressure of 6.41 MPa, a polymer solution of 5 mL/min, a CO2 flow rate of 2000 mL/min, a liquid CO2 level in the precipitator of 1/8, and a PS concentration equal to or less than 1 wt%. In the preparation of PS/PMMA blends, the obtained blends were mostly in submicron-sized particles for a temperature of 298 K, a pressure of 6.41 MPa, a polymer solution of 5 mL/min, a CO2 flow rate of 2000 mL/min, a liquid CO2 level in the precipitator of above 1/4, and a blending polymer concentration equal to or less than 1 wt%. When the blending polymer concentrations ranged between 2 and 8 wt%, the obtained blends were shown in submicron and micron-sized particles. By the way, a spherical blending polymer of PS/PMMA core/shell morphology could be observed for a PS/PMMA ratio of 9/1, a liquid CO2 level in the precipitator of 1/2, a PS molecular weight of 144,000, and a PMMA molecular weight of 36,000.
In Chapter 4, the measurement of diffusion coefficients of solutes in CO2-expanded liquids was described. Due to the low solubility of hydrogen in organic solvents, and the existence of interfacial resistance between gas and liquid phases, as well as the resistance of diffusion within the liquid, the reaction rate of hydrogenation reaction would be limited. When compressed CO2 was dissolved into the organic liquids, CO2-expanded liquids (CXLs) were formed. In CXLs, the solubility of hydrogen in organic liquids increased, and the density and viscosity of organic liquids decreased and thus the resistance of diffusion within liquids decreased. The diffusion coefficients of p-chloronitrobenzene in CO2-expanded methanol and the diffusion coefficients of benzonitrile in CO2-expanded ethanol were investigated in this chapter. Several variables including temperature, pressure, and the CO2 concentration in organic liquids were studied. It was found that the diffusion coefficients of solutes in CXLs were higher than those in pure liquids, indicating the benefit of the dissolution of CO2 in liquids for diffusion. For a fixed pressure, the diffusion coefficients of solutes were observed to increase with temperature. The diffusion coefficients of solutes were also found to decrease with increasing pressure at a fixed temperature. The corresponding equations of diffusion coefficients were established according to different systems of diffusion.

參考文獻

Abraham, G. A.; Gallardo, A.; Motta, A.; Migliaresi, C. and San Rom