有機改質多壁碳奈米管的合成及於高分子奈米複合材料的應用

Synthesis of organo-modified Multiwall carbon nanotubes (MWCNTs) and application for polymer/MWCNT nanocomposites

張家銘(Chia-Ming Chang)

指導教授 ： 劉英麟

中原大學/工學院/化學工程研究所/博士(2013年)

https://doi.org/10.6840/cycu201300619

摘要

在本研究中，主要在探討多壁碳奈米管的改質並藉由表面官能基化以增加與高分子間的相容性。藉由改變碳奈米管的化學結構、物理性質，研究在高分子複合材料中的應用。在本論文中，主要可分成兩種改質碳奈米管的方法，運用此方法得以開發出不同鍵結的有機改質碳奈米管。
第一種方法乃是利用分子設計觀點，利用碳奈米管管壁的五元環與六元環交錯所產生的雙烯(diene)與親雙烯(dienophile)結構，並透過Diels-Alder方式分別將帶有相對應官能基的親雙烯與雙烯結構分子與碳奈米管進行反應，利用傅立葉紅外光譜儀(FTIR)、熱重分析儀(TGA)與拉曼光譜儀(Raman)來確定DA反應確實可以與碳奈米管反應，且運用DA反應改質的碳奈米管具有加熱可逆的效果，從溶解度可以觀察到，改質後的碳奈米管可以分散在有機溶液中，在經過加熱後，即開始發生纏繞沉澱的現象。為了瞭解高分子對DA反應的反應性，在此也使用側鏈帶有maleimide的polyimide進行接枝，高分子改質之碳奈米管可以增加在溶液中的分散性。在應用方面，利用改質的碳奈米管與聚偏氟乙烯(PVDF)製成複合材料，隨著碳奈米管含量的增加，整體的導電性質會有增加的趨勢，其中令人感興趣的是，利用熱處理過後的複合材料其導電性可從2×10-12 S cm-1上升至4×10-8 S cm-1，這也表示利用DA反應改質的碳奈米管可以在極低含量的添加下，即可以達到導電的效果。
第二部分乃是在高分子鏈上以臭氧處理方式導入過氧化物基團，同時利用加熱斷鍵產生自由基原理將高分子導入碳奈米管表面。相較於傳統方法直接在碳奈米管表面進行臭氧處理產生環氧基，本方法更可以運用在各種無反應性工程塑料上。在此，利用臭氧處理將聚偏氟乙烯(PVDF)、聚碸(PSF)、聚氧二甲苯(PPO)與二氮雜萘聯苯聚醚酮(PPEK)修飾於碳奈米管表面，並以FTIR、光電子能譜儀(XPS)、TGA與Raman鑑定其結構，並佐以高解析穿透式電子顯微鏡(HRTEM)來觀察表面管壁之變化，這些檢測均可說明碳奈米管成功的被改質。將這些PSF與PVDF改質之碳奈米管加入PVDF中製成複合材料，可以觀察到選用基底材料(PVDF)改質的碳奈米管顯現出較佳的機械性質與電性質，這也指出，藉由選用與基底材料相同之改質碳奈米管可提升分散性，有效的改善無機材與有機材之相容問題；另一方面，在極微量之比例下(0.07%)，PVDF/MWCNT-PVDF會產生負載傳遞(load-transfer)現象使複合材料之延展性提升180倍。
此外，以臭氧聚合將聚電解質材料(Nafion、polybenzimidazole, PBI)修飾碳奈米管是一令人感興趣的研究，在此，將分為PBI與Nafion系統進行討論，藉由包覆電解質材料的碳奈米管形成質子傳導通道，可以有效的提升質子傳導率。在PBI系統中，碳奈米管的加入不僅可以提升燃料電池的性能更可以增強質子交換薄膜的機械強度。隨著改質碳奈米管的加入，其磷酸吸附量也會隨之增加，碳奈米管的加入可能會打斷分子間的作用力，使複合材料可以限制更多的磷酸分子，直接增加燃料電池的質子傳導率。另一方面，使用DA反應將Fe3O4粒子附著於碳奈米管上，再以磁場進行排列，以減少質子傳導路徑。從質子導電率的提升可以明顯的發現，排列後的碳奈米管確實可以有效的提升導質子的特性。但其中最令人感興趣的是，添加入含有Fe3O4粒子的碳奈米管可以抑制甲醇的透過，經X-ray小角散射儀(SAXS)、正子湮滅光譜儀 (PALS)證實此種碳奈米管的加入，可以縮減親疏水端的domain，限制甲醇的通過。在直接甲醇的測試中，添加入0.1%的改質碳奈米管其最高功率可達92.4 mW cm-2，經磁場排列後，更可以達到109.3 mW cm-2。

關鍵字

燃料電池 ； 奈米複合材料 ； DA反應 ； 改質 ； 臭氧 ； 碳奈米管

並列摘要

Functionilization of multiwalled carbon nanotubes (MWCNTs) is critical to increase the interphase compatibility between MWCNTs and the polymer matrix.In this work, two approaches have been explored and investigated to exctend the scopes of organo-modfied MWCNTs and their application in advanced nanocomposites of MACNTs and polymers.
The first approach involves Diels-Alder (DA) reaction for the functional- ization of MWCNTs. MWCNTs could serve as dienes or dienophiles in the DA reaction. A molecule or a polymer possessing diene or dienophile groups could be easily incorporated onto MWCNTs to result in the organo- functionalized MWCNTs. The performance of the DA reaction and the chemical structures of the functionalized MWCNTs have been demonstratyed with Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyzer (TGA) and Raman spectroscopy. Moreover, the adducts (the 6-member ring formation with the DA reaction) of DA reactions could undergo a reverse DA reaction (the retro-DA reaction) up heating to generate the component molecules.. As a result, the functionalization of MWCNTs is thermally reversible. The thermally-reversible feature has shown an attraction in preparation of electrically-conductive polymer/MWCNMT nanocomposites. Incorporation of the DA-adduct- functionalized MWCNTs into poly(vinylidene fluoride) (PVDF) increases the electrical conductivity of PVDF.After a thermal treatment, the sample possessing 0.5 wt % of functionalized MWCNT shows an increase in the electrical conductivity from 2×10-12 S cm-1to 4×10-8 S cm-1, as the performance of the thermally-induced retroDA reaction to recoverthe electrical conductivity of MWCMTs from defunctionalization. It is noteqorthy that the mechanical properties of the nanocomposites do not change with the thermal process. The results demonstrate an approach to employ small amount of MWCNTs for the preparation of electrically-conductive MWCNT nanoocmposites.
The second approach demonstrates the approach to chemically incorporate non-reactive polymer chains to MWCMTs through an ozone-mediated process. Ozonization of polymers generates peroxide and hydroperoxide groups in the polymer chains.These groups thermally decompose into oxygen radicals, which are reactive toward the bundles of MWCMNTs. In this work, four different polymers including poly(vinylidene fluoride) (PVDF), polysulfone(PSF), poly(2,6-dimethylphenylene oxide) (PPO), and poly(phthalazinone ether ketone) (PPEK) have been used to prepare polymer-functionalied MWCNTs through the ozone-mediated process. The chemical structures of the polymer-functionalized MWCNTs have been demonstratyed with FTIR, TGA, Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM). Matrix-polymer-functionalized MWCNTs are especially useful to increase the reinforcement efficiency for polymer-MWCNT nanocomposites because the chain entanglements between the bonded to MWCNTs and the matrix polymer, so as to increase the perfection of dispersion of MWCNTs in the matrix polymer and the load transfer efficiency from polymer matrix to MWCNTs. As a result, MWCNT-PVDF/PVDF nanocomposite shows better mechanical and electrical properties compared to the nanocomposites possessing the unmodified and PSF-modiofied MWCNTs. On the other hand, a small loading amount of MWCNT-PVDF (0.07 wt %) has shown a great efficiency on toughening PVDF with a 180-fold increase in the toughness of the polymer.
The ozone-mediated process has been utilized in preparation of Nafion- and polybenzimidazole (PBI)-functionalized MWCNTs (MWCNT-Nafion and MWCNT-PBI). The funtionalized MWCNTs have been utilized in the preparation of PBI/MWCNT nanocomposites for using as proton exchange membranes for fuel cells. The polyelectrolyte-fuctionalized MWCNTs not only enhance the mechanical property but also increase the proton conductivity of the membranes. In single fuel cell test at150℃, significant enhancement of cell performance has been obversed with the membranes modified with the polyelectrolyte-fuctionalized MWCNTs. Furthermore, MWCNTs which are anchored with Fe3O4 magnetic nanoparticles (MNP) and functionalized with Nafion has been prepared. Under a magnetic field, alignment of the MWCNTs has been observed to result in a further increase in the proton conductivity of the membrane. Moreover, the Fe3O4anchored MWCNTs block the methanol crossover of the membranes. With the results from small-angle X-ray scattering and positron annihilation lifetime spectroscopy, the hydrophilic clusters(contribute in to the methanol permeation) of the membrane have been altered with MWCNT-MNP-Nafion addition, so as to result in the decrease in the methanol permeability of the mmebranes. The increase in proton conductivity and decrease in methanol permeability result in the high cell performance of the membrane in single fuel cell test at 70℃ with a maximum power density of 109.3 mW cm-2.

並列關鍵字

nanocomposite ； carbon nanotube ； MWCNT ； modificaion ； ozone ； DA reaction ； fuel cell

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