| Summary: | 碩士 === 臺灣大學 === 材料科學與工程學研究所 === 98 === 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%.
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