Comparision of Processing, morphology and properties for acid modified and polyimide modified multiwalled carbon nanotube/polyetherimide composite

由於奈米碳管具有許多優異之材料、機械、熱傳導及導電特性，近年來引起廣泛的研究與討論，使其成為吾人在選用提升複合材料性質時的絕佳候選填充物。而聚醯亞胺高分子(Polyimide)是一具有高熱穩定性且良好的機械性質的高分子，同時又容易合成等性質。藉由將聚醯亞胺高分子與具有優異性質的奈米碳管相混合，形成具有高分子功能性之奈米複合材料。 本研究將分三部分來探討，第一部份先比較多壁奈米碳管(MWNT)藉由混酸溶液(硫酸:硝酸=3:1)酸改質2、4、6、12小時和純硝酸溶液酸改質24小時後的差異性，同樣以超音波震盪使奈米管懸浮並將奈米碳管表面改質，利用強酸溶液的氧化作用使得奈米碳管表面改質成帶有羧酸基(-COOH)以及氫氧基(-OH)。將實驗室現有的聚醚醯亞胺高分子先溶於氯仿溶液中（10wt%），然後分別配置不同含量的PEI/CNT-PAA改質碳管加入均勻混合後，得到聚醚醯亞胺/酸改質碳管(PEI/CNT-COOH)複合材料。 第二部份再將間-苯二胺(m-PDA)單體接枝在純硝酸改質後的奈米碳管表面上，再利用原位聚合法(in-situ)加入(1) 4,4’-(4,4’-Isopropylidenediphenoxy) bis(phthalic anhydride) (BPADA)與1,3-Phenylenediamine (m-PDA)和(2) 3,3'',4,4''-Diphenylsulfonetetracarboxylic dianhydride與9,9-Bis(4-aminophenyl)fluorene合成聚醯亞胺前驅物聚醯胺酸（PAA），形成PAA改質碳管(CNT-PAA)。再將實驗室現有的聚醚醯亞胺高分子先溶於氯仿溶液中（10wt%），然後分別配置不同含量的PEI/CNT-PAA改質碳管加入均勻混合後，藉由階段性加熱閉環步驟得到聚醚醯亞胺/聚醚醯亞胺改質碳管(PEI/CNT-PEI)以及聚醚醯亞胺/聚醯亞胺改質碳管(PEI/CNT-PI)複合材料。最後第三部份則是比較兩種不同的改質方式在導電度、機械性質、以及熱穩定度間的比較整理與討論。 本研究中使用高解析電子能譜儀(XPS)來鑑定多壁奈米碳管的改質效果，熱重損失分析儀（TGA）、微差掃描熱量分析儀(DSC)、萬能試驗機(Universal Test Machine)分別測定材料的熱穩定性質、玻璃轉移溫度和機械性質，傅立葉轉換紅外光譜儀（FTIR）來鑑定其化學結構，掃描式電子顯微鏡（SEM）與高解析穿透式電子顯微鏡(HRTEM)來觀察材料的剖面型態與高分子接枝後的奈米碳管和基材之間的分散性，聚醚醯亞胺和聚醯亞胺改質後在碳管表面上的厚度與結構的改變，最後用四點探針來量測材料的電性。 在本實驗結果中，我們藉由聚醚醯亞胺或聚醯亞胺以化學接枝的方式將碳管表面改質的方式成功克服了高含量的多壁奈米碳管混掺於聚醚醯亞胺的問題。且其複合膜材與單純酸改質的碳管相比具有相當優異的性質，如高導電度、良好的機械性質、以及高熱穩定度。從TGA, HRTEM, FT-IR數據中我們可證明聚醯亞胺成功接枝於多壁奈米碳管上，且從FESEM中可看出碳管均勻分散於聚醚醯亞胺基材中且彼此間具有良好的介面附著力。隨著碳管量的增加，Td以及Tg分別提升了約13度和11度。拉伸應力也較純聚醚醯亞胺提升最高上升到了171%。最後，當碳管量添加至10wt%，導電度由於碳管在膜材當中形成網狀結構最高可提昇至六個數量級以上。Multi-wall Carbon nanotubes (MWCNTs) have stimulated wide research activities in recent years because of the merits of their unique mechanical, thermal and electric properties. Polyimide also has good thermal stability, excellent mechanical property and good processability. It is conceivable that if we combined polyimide with MWCNTs, the resulting composite would possess both excellent properties. This research will divide into three parts. In the first part, multi-wall carbon nanotubes（MWCNTs）were acid-teated by the mixed acids of sulfuric and nitric acids for 2, 4, 6, 12 hours and by nitric acid for 24 hours. After surface treatments, the surface of MWCNTs contains carboxylic and hydroxyl groups. Then various amounts of the acid-treated MWCNTs were added to polyetherimide in chloroform solution to fabricate the PEI/CNT-COOH composites. In the second part, the acide-treated MWCNTs were reacted with 1,3-Phenylenediamine and then with oligo(amic acid) (PAA, precursor of polyimide) to obtain the PEI and PI modified MWCNTs, denoted as CNT-PEI and CNT-PI respectively. MWCNTs in different steps of modification were characterized by high resolution x-ray photoelectron spectrometer (XPS), fourier transform infrared spectrometer (FTIR), transmission electron microscopy (TEM) and high-resolution transmission electron microscope (HRTEM). By addition of CNT-PEI and CNT-PI in different amounts to polyetherimide in chloroform solution, a series of PEI/CNT-PEI and PEI/CNT-PI composites were fabricated after drying and thermal imidization treatments. In part three, we compared the properties for the acid-treated and polyimide-modified CNT/polyetherimide composite, such as electrical conductivity, mechanical properties, and thermal stability. Their degradation behavior, glass transition temperature (Tg) and mechanical properties were investigated by thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC) and universal test machine, respectively. The morphology of composites after fracture was investigated by scanning electronmicroscopy (SEM). The electrical conductivity was measured by conductance meter. The experimental results indicated that the employment of CNT-PEI or CNT-PI have successfully overcome the obstacles to disperse the high content of MWCNTs in PEI. The resulting nanocomposites showed unique properties, such as high electrical conductivity, high mechanical properties, and high thermal stability. FESEM revealed the well dispersion of MWCNTs in PEI matrix. The presence of the MWCNTs has increased thermal decomposition temperature (Td) and glass transformation temperature (Tg) of PEI about 13◦C and 11◦C. The tensile strength of the nanocomposites films exhibited a remarkable increase of 171% as compared to the pure PEI. The electrical conductivity was also increased more than six orders than pure PEI films as the content of MWCNTs was increased to 10 wt%