Functionalization And Properties Of Polymide Nanofiber

Aromatic polyimides have been extensively investigated for their excellent thermal stability and high mechanical properties, along with their good chemical resistance and electrical properties.Continuing research interests are devoted to further improving the performance of polyimides in some specific applications. Polymer nanocomposites have been extensively investigated for their potential wide applications because of their easy processability, low-cost manufacturing, good adhesion to substrates, and unique physicochemical properties. Unique physicochemical phenomena such as giant magnetoresistance(GMR) or tunneling magnetoresistance(TMR) could be created, in which the nonmagnetic conductive or insulating polymer serves as a spacer. This phenomenon is completely beyond the simple addition of the advantageous physicochemical properties of a single polymer matrix and inorganic fillers, and a typical application of polymer nanocomposites is GMR/TMR sensors. Various nanomaterials have been explored for polymer nanocomposite fabrication, including transition metals and rare earth oxides, such as Fe2O3, Co Fe2O4, and Pt-loaded Ti O2.One dimensional nanocomposite fibers have attracted much interest due to their enhanced electrical, electronic, optical and chemical characteristics and wide potential use in applications such as sensors, filtration membranes, microelectronics and photonic devices, structural reinforcement, defense and security, and energy generation. Among them, electrospinning is the most handy, low-cost and high speed method to produce nano or nanocomposite fibers. In this paper, the PI, PI/g-Fe2O3 and PI/Ti O2 nanocoposite fibers were prepared by electrospinning and thermal imidization process. The influence factors of preparation of nanofibers and the effects on the structures and properties of nanofibers were studied. In the work, PI namofiber webs were activated, and the effects of technological parameters in the process of activation on the yield, structures and properties of nanofibers were investigated.The traditional two-step process of preparing polyimide nanofiber was used in this paper. The precursor polyamic acid(PAA) solutions were synthesized from pyromellitic dianhydride(PMDA) and 4,4’-diaminodiphenylether(ODA) by copolymerization in polar solvent dimethylformamide(DMF), and the nanofibers of PAA were prepared by electro-spinning. The polyimide nanofibers were obtained through thermal imidization at different thermal imidization temperatures and for different imidization time. The influences of different imidization temperatures and time on morphology, chemical structure, thermal stability and mechanical properties of the polyimide nanofibers were investigated by Fourier Transform Infrared Spectroscope(FT-IR), Scanning Electronic Microscope(SEM), thermal gravimetry analysis(TGA) and Electromechanical Universal Testing Machine. The experimental results showed that the imidization of PAA nanofibers was complete under 350℃ for 30 min.The polyimide(PI)/g-Fe2O3 nanocoposite fibers with magnetic behavior were prepared by electrospinning from polyamic acid(PAA)/Fe3O4 solution, followed by thermal imidization process. The effect of Fe3O4 nanoparticles content in precursor mixture solution on the properties of PI/g- Fe2O3 nanocomposite fibers was studied. The fibers were characterized by Fourier Transform Infrared Spectroscope(FT-IR), X-ray diffraction(XRD), transmission electron microscopy(TEM), scanning electron microscopy(SEM). The magnetic and mechanical properties of the electrospun PI/g- Fe2O3 nanocomposite fibers were also investigated. The study showed that magnetic nanoparticles existed in the nanofibers by the form of physical composite, and with the increasing of the Fe3O4 content, the nanocomposite fibers became thiner, the break strength and elongation at break of the fiber membranes slightly decreased, and the saturation magnetization increased.The PI/Ti O2 nanocoposite fibers were prepared by electrospinning and thermal imidization process. The study showed that the nanocomposite fibers became thiner with the increasing of the Ti O2 content, and the thermal-decomposition temperature and the mechanical properties slightly decreased, compared with pure PI fibers. The photocatalytic properties of samples were analyzed through the degradation of methylene blue. The PI/Ti O2 nanocoposite fibers prepared by electrospinning had certain photocatalytic performance, and the higher content of Ti O2, the faster the degradation rate, and with the extension of degradation time, the degradation rate gradually decreased.In this work, PI namofiber webs were chemically activated, and the effects of technological parameters on activation yield were investigated. By means of the orthogonal experiment, the optimum process conditions of the activation reaction were determined, namely the phosphate concentration was 6%, the soaking time for 20 min, activation time for 20 min, the heating rate of 2℃/min, and the activation temperature of 700℃. The effects of activation temperature on the structures and properties of nanofibers were studied in this paper. The study showed that the nanofibers became thiner, the mechanical properties seriously decreased, the carbon content gradully increased, and the content of nitrogen and oxygen gradully declined. When the activation temperature was 700℃, the nanofiber membranes mainly possessed micropore and mesoporous structures, and having high specific surface area, while specific surface area declined when the activation temperature was 900℃. The nanofiber membranes had a good adsorption performance for organic saturated steam. The influence factors of preparation of nanofibers and the effects on the structures and properties of nanofibers were studied. In the work, PI namofiber webs were activated, and the effects of technological parameters in the process of activation on the structures and properties of nanofibers were investigated.