奈米高分子複合材料的製備與性質

Abstract

本論文首先使用溶液摻合與熔融摻合製備對排聚苯乙烯(s-PS)/黏土(clay)奈米複合材料，並藉由適當的界面活性劑(CPC)，成功的製備對排聚苯乙烯/黏土奈米複合材料。黏土在對排聚苯乙烯中的分散性可由X光繞射儀(XRD)與穿透式電子顯微鏡(TEM)的分析來說明，結果顯示基材中的無機矽酸鹽層具奈米分散效果，是否添加界面活性劑將造成基材中的無機矽酸鹽層呈現1~2 nm 或數十至100 nm。界面活性劑(CPC)與對排聚苯乙烯彼此部分相容，將可使高分子鏈段藉由溶液摻合與熔融摻合進入黏土層間。而由微分掃瞄熱分析儀(DSC)等溫結晶與FTIR的測試可得知對排聚苯乙烯的a- 與 b-結晶型態，結果顯示不論以熱結晶或冷結晶處理，黏土在對排聚苯乙烯奈米複合材料中皆有助於b-結晶型態的生成。 其次本論文探討黏土在對排聚苯乙烯中所引發的結晶效果，在240℃等溫結晶過程中，使用Avrami方程式探討黏土含量與黏土/界面活性劑陽離子當量變化對結晶動力學參數的影響。對排聚苯乙烯/黏土奈米複合材料相較於對排聚苯乙烯有較快的結晶速率，說明奈米分散之矽酸鹽層具有促進結晶作用，並將改變結晶區域的大小。 另一方面，藉由合成之vinyl benzyl dimethyl ethanol ammonium chloride (VBDEAC)陽離子界面活性劑來與蒙脫土(MMT)進行陽離子交換反應，進而使用聚合方式製備剝離型聚苯乙烯(PS)/黏土奈米複合材料。蒙脫土層間的無機鈉離子藉由在水溶液中加入含銨鹽陽離子的VBDEAC進行陽離子交換而達到膨潤的效果，而聚苯乙烯/黏土奈米複合材料則是藉由加入苯乙烯單體與經膨潤處理過之蒙脫土均勻混合，再進行自由基聚合反應而得。黏土在聚苯乙烯基材中的分散性可藉由X光繞射儀測量黏土撐開層間距離而得，本實驗結果顯示其層間距離大於17.6 nm。而奈米複合材料的各項性質則可由DSC、TEM以及熱重損失分析儀(TGA)測試而得。由實驗結果可知，以前面方法所製備之聚苯乙烯剝離型奈米複合材料具有比聚苯乙烯材料更佳的熱穩定性與機械性質。 本論文亦使用聚合方式製備對排聚苯乙烯/黏土奈米複合材料，以X光繞射儀探討黏土在對排聚苯乙烯中的分散性，並以DSC與FTIR得知對排聚苯乙烯的結晶性質。本篇論文中提出兩個主要的目的，第一為藉由黏土的分散性探討對排聚苯乙烯奈米複合材料的結晶行為與型態；其次更重要的，黏土的分散效果對於對排聚苯乙烯經過熱結晶與冷結晶處理後相對結晶度的影響。

Syndiotactic polystyrene/modified-clay nanocomposites have been prepared by solution blending and melt blending by mixing pure s-PS and organophilic clay with adsorbed cetyl pyridium chloride (CPC). The dispersibility of the clay in syndiotactic polystyrene/modified-clay nanocomposites was studies using X-ray and transmission electron microscopy (TEM). The clay is well dispersed into the s-PS matrix using solution blending and melt blending with scale in 1~2 nm or in a few tenths ~ 100 nm depending on surfactant treatment. The CPC is partially compatible with s-PS and allows syndiotactic polystyrene chains intercalating into clay layers. The crystallization behavior of a- and b-crystals for syndiotactic polystyrene nanocomposite has been thoroughly examined using the Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC). Our results further demonstrate that the presence of the clay plays a vital role in facilitating the formation on the thermodynamically more favorable b form crystal when the s-PS is melt- or cold-crystallized. This study investigates the effects of montmorillonite (clay) on the crystallization kinetics of syndiotactic polystyrene (s-PS) using isothermal DSC analyses. For a crystallization temperature of 240℃, the isothermal crystallization data are fitted well by Avrami crystallization equation. The crystallization data on the kinetic parameters, k, n, clay content, and clay/surfactant cation exchange ratio have also been investigated. Experimental results indicate that the crystallization rate constant (k) of the s-PS nanocomposite increases with increasing clay content. The polymerizable cationic surfactant, vinyl benzyl dimethyl ethanol ammouium chloride (VBDEAC), was synthesized to functionalize the montmorillonite (MMT) clay and used to prepare exfoliated polystyrene-clay nanocomposites. The organophilic MMT was prepared by cationic exchange between inorganic Na+ cations of the montmorillonite and ammonium cations of the VBDEAC in an aqueous medium. Polystyrene-clay nanocomposites were prepared by free-radical polymerization of the styrene containing intercalated organophilic MMT. Dispersion of the intercalated montmorillonite in the polystyrene matrix determined by X-ray diffraction reveals that the basal spacing is higher than that of 17.6 nm. These nanocomposites are characterized by differential scanning calorimetry (DSC), transmission electron micrograph (TEM), thermal gravimetric analysis (TGA) and mechanical properties. The exfoliated nanocomposites have higher thermal stability and improved mechanical properties than the pure polystyrene. This study also prepares s-PS/clay nanocomposites by the polymerization. The X-ray is used to characterize clay dispersibility in the s-PS matrix. FTIR is applied to characterize the changes of crystalline form in the s-PS containing clay. The DSC analyses are also conducted to examine the effect of the clay on crystallization behavior of s-PS/clay nanocomposites. Two goals are pursued in this study: (1) detailed characterization of crystallization behavior and morphology of the s-PS caused by clay dispersibility; and (2) more importantly, examining the effect of clay dispersibility on crystallinity of s-PS samples during melt- and cold-crystallization. The observed crystallization behavior and crystallinity provide valuable information regarding the effect of clay on crystallization behavior of the s-PS.