聚胺酯/黏土及聚己內酯/黏土奈米複合材料之合成與分析

Abstract

天然黏土是一種無機矽酸鹽層狀材料，地層內具有豐富之含量，此無機層狀材料以蒙特石最具代表性，其是由兩個矽氧四面體和一個鋁氧八面體組成的結構，靠著凡得瓦爾力結合，而晶層間具有離子鍵結的金屬陽離子，此即為有機分子和黏土進行離子交換的位置。黏土主要是由數個主要顆粒所聚集而成，其大小約為0.1∼10μm，而主要顆粒又是由數個單位晶體所組合而成。主要顆粒的高度約為80A∼100A，而單位晶體之厚度約為9.6A∼10A，因此每個主要顆粒是由8∼12個單位晶體所構成。 高分子/黏土奈米複合材料之發展始於日本豐田公司，首先開發出Nylon/clay奈米複合材料，並已正式商業化，由於其具有輕量化，良好的機械性質、熱性質等優點，此乃傳統複合材料所無法達到之特性，因此引起廣泛的注意，後續投入研究者眾多。 本研究中主要是以製備聚胺酯/黏土奈米複合材料為出發點，利用了兩種不同的製程來製備，另外從聚己內酯/黏土奈米複合材料之製備中探討其結晶形態學及確定己內酯單體在不同有機黏土存在下其開環反應機構。 在探討有機黏土對環狀單體的開環聚合反應行為時，發現己內酯單體之開環反應機構是以二個階段完成，第一階段是在較低溫下，己內酯單體在矽酸鹽層的長廊（gallery）中和有機膨潤劑的官能基或矽酸鹽層上的胺陽離子進行開環起始反應。第二階段反應發生在較高的溫度，此時具活性的聚己內酯分子鏈和大量擴散進入矽酸鹽層的己內酯單體繼續進行成長反應，並導致矽酸鹽層在聚己內酯基材內形成脫層。另外在反應活化能之研究，發現隨著有機黏土含量的增加，第一階段己內酯單體開環起始反應之活化能亦隨著增加，但是第二階段的聚己內酯成長反應之活化能則隨著降低。對於聚己內酯/黏土奈米複合材料結晶形態學之研究，從偏光顯微鏡和X-光繞射儀之觀察，發現隨著有機黏土含量的增加，會降低聚己內酯結晶顆粒的大小及結晶度，但其並不會影響其晶體成核成長的形狀。 對於聚胺酯/黏土奈米複合材料之製備，本研究利用了合成法及溶液摻合法兩種製程，經X -光繞射儀及穿透式電子顯微鏡的觀察，證實已成功的製備了矽酸鹽層均能脫層並以奈米尺寸分散在聚胺酯基材中，其製備方法分別如下所示： (1) 合成法：利用具低分子量（約3300g/mole）的聚己內酯/黏土奈米材料，由於其末端具有氫氧基，在聚胺酯的合成過程中，取代了硬鏈段中部份的1,4-BG，並和MDI，polycaprolactone diol (Mn = 1000)，1,4-BG共同製備成聚胺酯/黏土奈米複合材料。當聚己內酯/黏土的含量(mole%)為1.4時，所製得的聚胺酯/黏土奈米複合材料和純聚胺酯樹脂比較，其伸長率從103% 提升至690%，且其抗張強度亦隨著增加，當聚己內酯/黏土之含量達4.2%時，其伸長率則大幅降低至57.5%，但其機械強度仍持續增加，此現象顯示，當聚己內酯/黏土的含量增加時，所製備的聚胺酯/黏土奈米複合材料之特性將從一聚胺酯彈性體轉變成熱塑性聚胺酯樹脂。 (2) 溶液摻合法：利用含12個碳鏈的胺基酸（12-aminolauric acid）及Benzidine當有機膨潤劑，處理含鈉的蒙特石（Na+-montmorillonite），形成有機黏土（12-COOH-mont及BZD-mont），並將其分別以1, 3, 5 wt%的添加量加入MDI、PTMEG及1,4BG中製備聚胺酯/黏土奈米複合材料，經X-光繞射儀及穿透式電子顯微鏡的觀察得知，1, 3, 5 wt%的12COOH-mont/PU及1, 3 wt%的BZD-mont/PU均能形成聚胺酯/黏土奈米複合材料。從熱差掃描卡計（DSC）分析其玻璃轉移溫度及霍氏紅外線光譜儀（FTIR）分析其相分離度時發現有機黏土的添加量並不會改變聚胺酯的化學結構，當以1wt%的BZD-mont添加時所製備的聚胺酯/黏土奈米複合材料其抗張強度及伸長率和純聚胺酯樹脂比較時，發現其分別增加了2倍（從66.8kgf/cm2增加至144/kgf/cm2）及3倍（從220%增加至680%），另外在吸水率方面，1wt% 12COOH-mont/PU及1wt% BZD-mont/PU皆顯示有降低之趨勢。

Montmorillonite is a type of natural clays and consisted of two SiO2 tetrahedrons attached to one Al2O3 octahedron. Through van der Waals force the metallic ions and ionic bonds between crystalline layers provide sites for ion exchange by organic molecules. These silicate layers dimensions were 100 nm x 100 nm x 1 nm, and carried negative charges, causing an absorption of cations such as sodium (Na+) or calcium (Ca+2). The present research is concerned with the preparation of polyurethane/clay nanocomposites with two methods. Additionally, the investigations on the crystalline morphology and the reaction mechanisms of caprolactone monomer in the presence of various types of organoclay were studied. The reaction mechanism of polycaprolactone (PCL) /clay nanocomposites synthesized from organic modified clay (organoclay) and caprolactone (CL) monomers was investigated with differential scanning calorimetry and X-ray diffraction. It was found that the polymerization process of caprolactone in the presence of organoclay proceeded in two stages. The first stage occurred at low temperature, and it involved the initiation of ring-opening of caprolactone in the interlayer gallery of silicates by the functional groups of the swelling agents. The second stage took place at higher temperatures where the propagation of the active polycaprolactone chains progressed by a massive diffusion of caprolactone near the chains as the silicate layers exfoliated in polycaprolactone matrix. The activation energy of the first stage reaction increased, while the activation energy of the second stage reaction propagation decreased with the increasing amount of organoclay. Both of the activation energies depended on the type of swelling agent. The crystal sizes and crystallinity of polycaprolactone decreased with the increasing amount of organoclay, with the shape of growing crystals remained unchanged, as evidenced by X-ray and polarized microscope results. The descriptions of these two processes are as following: (1) Synthetic method: The synthesis of polyurethane/clay nanocomposites involved a reaction of the mixtures of 1, 4-butanediol (1, 4-BG), 4,4'-diphenylmethane diisocyanate (MDI), polycaprolactone diol (Mn~1000) and polycaprolactone/clay (PCL/clay) diol, with PCL/clay first being synthesized following the procedure in the literature. The elongation at break (EB) for polyurethane/clay nanocomposites containing 1.4 mole % PCL/clay had a six-fold increase as compared to that of the pure PU (i.e. 690% vs. 103%). However, the EB for PU/clay containing 4.2 mole % PCL/clay dropped significantly to 57.5%, but the maximum strength of the PU/clay still increased with the amount of PCL/clay. This implied that the properties of PU/clay changed from that of polyurethane elastomer structure to thermoplastic polyurethane structure at high PCL/clay content. (2) Solution blending process: The PU/clay nanocomposites was also synthesized by directly mixing of PU and organoclay such as 12COOH-mont and BZD-mont in DMF, and intercalated 1, 3 wt% clay/PU nanocomposites were formed. It was found that the chemical structures of the PU were not affected by the presence of organoclay from the FT-IR study. By comparing the tensile strength and elongation ratio of 1wt% BZD-mont, the prepared polyurethane/clay nanocomposites with these of polyurethane resin, the increase was twofold for tensile strength from 66.8 kgf/ cm2 to 144 kgf/ cm2, and three-fold for elongation at break for 220% to 680%. The water absorption ratios for both 1wt% 12-COOH-mont/PU and 1 wt% BZD-mont/PU also showed decreasing trend.