Constructing Of Polyaniline Composite Materials And Dissolution Of Polyaniline At Low Temperature

In2000, Alan Heeger, Alan MacDiarmid and Hideki Shirakawa were awarded by the Chemistry Nobel Prize in recognition of their outstanding professional contributions to the conducting polymers materials science. The discovery of conducting polymers break through the concept of organic materials behaving as traditional insulators but as metals or semiconductors. The doped and undoped states have very different properties in electronic, optical, physical, chemical, and electrochemical aspects, driving many advances in materials science, electronic theory and technological applications. In the21st century, The development of new functional materials based on environmental friendly renewable materials has already become the focus studied and front field. Incorporating natural polymer with conducting polymer is a promising approach to achieve a trend of being biocompatible, lightweight and lower-cost functional materials. Among intrinsically conducting polymers, polyaniline (PANI) is an unique and important conducting polymer because of its controllable chemical and physical properties, which depend on its oxidation and protonation states. The difficulty in its processibility limited the application on a large scale for the industrial application. We hope to create a simple method to fabricate the PANI/cellulose composites, actualizing the processing ability of polyaniline. On the basis of the promotion on a dissolution process of macromolecules by hydrogen bonds interaction, we tried to dissolve polyaniline in NaOH/urea/cellulose aqueous solution through hydrogen bonding association between the-NH groups of PANI and the-OH groups of the cellulose ICs, and revealed the structure and properties of films, fibers, hydrogels and microspheres fabricated by the PANI/cellulose solution. To actualize the dissolution of polyaniline at low temperature and the applications, a series of scientific question must be resolved. Why hydroxide/urea/cellulose aqueous solution can dissolve polyaniline? How about the rheological behavior of PANI/cellulose solution? How to fabricate the PANI/cellulose functional materials? Thus, the present studies were focused on the PANI/cellulose solution and the functional materials from them in systematical.The novel creations of this work are as follows:(1) for the first time, polyaniline (PANI) doped with acidic phosphate ester was dissolved successfully in NaOH/ureac/cellulose system with cooling, and it was revealed that the PANI dissolution in the cellulose aqueous solution arises as a result of a complexation between PANI and cellulose through hydrogen bonds.(2) It was clarified that the miscibility, rheological properties and the sol-gel behavior of the PANI/cellulose complex solution.(3) Novel PANI/cellulose fibers composite, hydrogels and microspheres were prepared from the PANI/cellulose solution, and the structure and properties of the materials were indicated.(4) The PANI/cellulose films were obtained by using regenerated cellulose as templates, and the functional materials can be used as lightweight and flexible electrode materials for supercapacitors. The main contents and conclusions in this thesis are generalized as follow:For the first time, polyaniline (PANI) doped with acidic phosphate ester was dissolved successfully in the cellulose aqueous solution in7wt%NaOH/12wt%urea system with cooling. The results of13C NMR and dynamic light scattering (DLS) confirmed that the PANI dissolution in the cellulose aqueous solution arises as a result of a complexation between PANI and cellulose through hydrogen bonds. The results of SEM, AFM and DSC revealed that good miscibility between PANI and cellulose existed in the composite films, as a result of the association of the two components held together by noncovalent interaction. PANI dissolution in the cellulose aqueous solution was a physical process. From the composite solution, dark green and transparent PANI/cellulose films were constructed facilely, displaying the issue of improving processability of PANI. The PANI/cellulose films exhibited highly homogeneous porous structure and good mechanical properties. Moreover, the conductivity of the PANI/cellulose composite films doped by acidic phosphate ester, HCl and carbon black was improved significantly. This work has opened up a completely new avenue to construct the supramolecular materials from the intransigent cellulose and enticing PANI via a simple, facile and environmentally friendly process for a variety of applications.To further understand the miscibility and processability of the complex solution, the dynamic rheological behaviors of the PANI/cellulose complex solution have been investigated. Transmission electron microscope (TEM) results demonstrated that the inclusion complexes consisted of PANI and cellulose existed in the aqueous solution, showing a good miscibility. Time-temperatures superposition (tTs) results indicated that the PANI/cellulose solution exhibited homogeneous system in the temperature range from0to25℃, and the complex solution was more stable than the cellulose solution. At higher temperatures, the urea shell of the cellulose IC was destroyed and the-OH groups of the cellulose ICs was exposure to form hydrogen bonding association between cellulose chains. As a result, the PANI/cellulose supramolecular complex solution was changed to gels through the physical cross-linking and chains entanglement at elevated temperature. This further demonstrated that the gel formation was dominated by the self-association of the cellulose. Larger flow activation energy of the PANI/cellulose solution suggested a relatively stiffer conformation of the complexes. Winter-Chambon theory was proved to be capable to describe the gelation behavior of the PANI/cellulose complex solution, the gelation of the cellulose solutions took place at lower temperature or higher temperature, and was a thermo-irreversible process. However, the PANI/cellulose solution remained a liquid state for a long time at the temperature range from0to8℃, which is important for the industry process.PANI/cellulose composite fibers were spun successfully on a small and simple homemade wet-spinning apparatus. Morphology, structure and properties of PANI/cellulose fibers were characterized by SEM and mechanical testing. The polyaniline/cellulose solution coagulated with10wt%H2SO4aqueous during the spinning and coagulation process. PANI/cellulose fibers had circular cross section and ripple surface. With the increasing of the spinning draw ratio, the pore diameter and tensile strenghth of the PANI/cellulose fibers increased, whereas the elongation at break decreased. An electromechanical polyaniline/cellulose hydrogels were prepared from PANI/cellulose solution by using epichlorohydrin (ECH) as a cross-linker. These hydrogels had excellent mechanical properties, and exhibited a continuous and linear motion under the applied electric field. The average crawling speed increased with the polyaniline content increase, indicating that polyaniline played vital roles on their electromechanical actuations. The PANI/cellulose microspheres were successfully prepared by different method. The size of the PANI/cellulose microsphere was adopted as dispersed materials for electrorheological fluids.By using porous regenerated cellulose film as template, aniline could be polymerized either on the surface or in the bulk by chemical oxidative techniques. From the SEM and TEM results, the distribution of polyaniline in cellulose matrix was in a regular state. Polyaniline chains grew from the inside to the outside with an increases of polyaniline density. Finally, pure polyaniline layer with the thickness of ca.8um was combined closely with cellulose surface. Electrochemical measurements in H2SO4aqueous confirm the presence of two prominent redox peaks consistent with polaron and bipolaron formation processes. PANI/cellulose films exhibited highly flexible state, and a high specific capacitance of495.7F/g for the electrode materials at a current density of0.2A/g, well cycle stability after1200cycles. Moreover, the specific capacitance only had a little decrease with the increase of current densities. The Coulombic efficiencies at different current densities were almost kept constant at90%. This conductive flexible composite film showed large electrochemical properties.In order to enhance the electrochemical properties of PANI composites films, carbon nanotube (CNT) was dispersed in NaOH/urea aqueous solution to prepare the free-standing, and flexible PANI/CNT/cellulose (PCN) paper. The morphology and microstructure of the obtained products were characterized by SEM, FTIR and XRD. PANI nanofibers grew either on the surface or in the bulk of the CNT/cellulose films, forming a thin, lightweight and flexible composite paper. The resulting PCN6composite paper displayed optimal electrochemical capacitance, making it attractive for high performance flexible capacitors. The results of electrochemical tests indicated that PCN6paper electrodes not only displayed a high specific capacitance of871F/g at the current density of5mA/cm2, with a retention ratio of78%after1000cycles, but also retained a specific capacitance of nearly703F/g and a coulombic efficiency of99%at a high current density of5mA/cm2. The good performance of PCN was attributed to macroporosity architecture.This thesis provided a novel process for dissolving PANI, and the porous regenerated cellulose films as template, fabricating lightweight and flexible PANI/cellulose composites, which opened up a new avenue to process polyaniline. This work presented important science dates for the preparation of the functional materials through a "green" method by using natural polymer and conducting polymer. Therefore, there were great scientific significance and prospects of application, and it well accorded with the target of our country to develop and utilize the natural polymer resources.