Preparation And Study Of High Performance Polymer/Carbon Nanotubes Composite Films

Since the first observation of high performance polymers in USA at the end of 50's, extensive research in this subject has been aroused. As most important part of polymer materials, high performance polymers have been widely used in the fields such as aerospace, electronics, micro electronics, fine mechanic tools, nuclear industry, as well as separation membranes, liquid crystal display, and Langmuir-blodgett films, owing to their excellent thermal stability. As the development of the technology of synthesis and process, the application of high performance polymers have been enlarged into wider areas, such as automobile, electronic appliance, office products, and or so.As the rapid development of aerospace technology all over the world, all kinds of high performance polymer films have been widely used. Several space mission concepts proposed by NASA are based on the use large, deployable, and ultra-lightweight vehicles (e.g. Gossamer spacecraft) consisting of both structural and polymer film components.However, future Gossamer spacecraft will require films that are durable to the space environment and compliant. Compliance is needed so that the film can be folded into caompact volumes found on conventional launch vehicles. Once in orbit, the folded film is deployed to create structures, that are many square meters in size. To be space durable, the film must exhibit resistance to many environment factors, such as atomic oxygen (AO) in low earth orbit, UV and vacuum UV radiation, and electron and proton attack. Therefore, high performance films are needed to meet these requirements.However, as far as the application of high performance polymers are concerned, the static electricity is becoming a big problem. Generally speaking, high performance polymers are kinds of insulating materials. Therefore, electric charge accumulation can easily take place at the surface of the polymers, as a result, the static electricity can be formed, which may bring many hazards.As the electric charge accumulation takes place, the surfaces of high performance polymers can absorb dust easily and will be very dangerous while touching. Meanwhile, the material can then behave like a capacitor and discharge in a single event causing considerable damage to surrounding materials and electronics on the vehicles.Therefore, it's becoming vital to prepare anti-static high performance polymer films, which can be widely used for the following filds: (1)packaging materials; (2)for solar cell usage. It require that the films for both applications exhibit low solar absorptivity (α)and high thermal emissivity (ε), i.e., the film has anti-static properties while maintaining its own transparency.The most effective method for charge mitigation is to endow the insulating materials conductive properties. As we know, the charge can mitigate easily on the conductive surface. As far as the anti-static high performance polymers are concerned, it's necessary to modify the high performance polymers, while maintaining the excellent mechanical and thermal properties of high performance polymers. The current state-of-the-art to impart electrical conductivity while maintaining a lowαand high optical transparency has been through the use of conductive coatings such as indium-tin oxide (ITO). While exhibiting high surface conductivity, these coatings are rather brittle and make handling difficult. Once the coating is broken (cracked) by handling or on orbit, the conductive pathway is lost.Since the discovery of nano materials, the research focued on the polymer/nano materials nanocomposite have been aroused much attention. Especially carbon nanotubes, since their discovery in 1991, they have captured the attention of researchers worldwide. Understanding their unique properties and exploring their potential application have been a main driving force for this area.In terms of mechanical properties, nanotubes are among the strongest and most resilent materials known to exist in nature. A nanotube has Young's modulus of 1.8 TPa and a tensile strength about a hundred times higher than steel and can tolerate large strains before mechanical failure. Therefore, Nanotubes can be used as an excellent candidate for enhancement application in the fields such as aerospace, automobile, ship, sport products, etc.Extensive studies have been shown that a nanotube can behave as a well-defined metallic, semi-conducting or semi-metallic wire depending on its chirality and diameter. Therefore, they can be used as anti-static materials effectively.The aim for this thesis is to modify the high performance polymers by carbon nanotubes and to obtain anti-static high performance polymers/carbon nanotubes nanocomposite films, which may have potential applications in aerospace application. Generally, the introduction of carbon nanotubes into polyarylene ether nitrile has little effect on the mechanical properties of polymer matrix. Therefore, in our work, carbon nanotubes embedded in a polymer film with a gradient distribution were successfully obtained. For composite films with gradient distributions of carbon nanotubes, the upper surface behaves as an intrinsic insulator, while the lower one behaves as a semiconductor, or even as a conductor. It is also found that with an increase of 1 wt% carbon nanotubes, the resistance of the bottom surface decreases by 2-3 orders of magnitude, as compared with pure polyarylene ether nitrile; furthermore, when the proportion of carbon nanotubes increased up to 5 wt%, the resistance of the bottom surface shows only very little changes. As a result, sufficient matrix conductivity of the bottom surface could be achieved at a lower filler concentration with carbon nanotubes in a gradient distribution. Meanwhile, the thermal stability, glass transition termperature and tensile properties of the matrix are maintained. There is considerable interest in such gradient composite films, which could be applied in the electrical engineering, electronics and aerospace fields, for their excellent mechanical properties, thermal stability and novel electrical properties.In order to obtain efficient dispersion of carbon nanotubes in polymer matrix, it's necessary to modify carbon nanotubes. At first, we purified carbon nanotubes by ultrasoncating them in the strong acids (H2SO4/HNO3, 3:1). There were many carbonyl acid groups attached on the carbon nanotubes after acid treatment, which had been proved by FTIR. At the same time, the content of carbonyl acid groups had be quantitatively determined by the titration. The purified carbon nanotubes could be acylated easily while refluxing in SOCl2. All of carbonyl acid groups on the surface and at the end of carbon nanotubes attended the reaction and changed to acyl chloride groups after refluxing for 24 hours. The acyl chloride groups played important roles in the chemistry of carbon nanotubes, since they could react with hydroxyl groups and amine groups easily. Therefore, we tried to react these acylated carbon nanotubes with lysine, and to obtain water dispersible lysine modified carbon nanotubes.As the development of multi-functional materials in the fields such as aerospace, electronic packaging materials, the optical transparent anti-static polymer films are becoming more and more important. Therefore, it's meaningful to develop anti-static films with optical transparency in our work.Therefore, multi-walled carbon nanotubes (MWNTs) modified PAEK nanocomposites were synthesized by in situ polymerization of monomers of interest in the presence of pre-treated MWNTs here. This process enabled uniform dispersion of MWNT bundles in the polymer matrix. The resultant MWNTs-PAEK nanocomposite films were optically transparent with significant mechanical enhancement at a very low loading (0.5 wt %). These MWNT-polymer nanocomposites are potentially useful in a variety of aerospace and terrestrial applications, due to their combination of excellent properties of MWNTs with PAEK. However, the resistance of the nanocomposite films didn't reach the anti-static orders.It's becoming urgent to develop this kind of materials. We tried another polymer matrix, polyimide. A process to efficiently disperse MWNT bundles in polyimide is carried out in this work. This process involves in situ polymerization of the monomers of interest in the presence of acylated MWNTs during the polymerization process. The acyl groups associated with the MWNTs attended the reaction through forming amide bonds. The goal of our work was to develop a method to completely disperse MWNT bundles into a given high perfomance polymer matrix on nanoscale level to produce a mechanically reinforced and optically transparent nanocomposite film with anti-static property. And the results showed that the obtained MWNTs-polyimide nanocomposite films were optically transparent with significant mechanical enhancement at a very low loading (0.5 wt %). Furthermore, the introduction of carbon nanotubes had decreased the resistance of composite films largely, and the obtained composite films exhibited anti-static property, which can satisfy the requirement of optical transparent anti-static films application. Meanwhile, the resistivity of the composite films can be further lowered by introduction a little amount of Cu ions.