The Study On Structural Regulation And Performance Of Electrospun PMIA Nanofibers

Poly(m-phenylene isophthalamide)(PMIA), which has meta-typebenzene-amide linkages in the skeletal chain with the strong ydrogen-bonded network structure, shows especially prominent thermostability, high flame retardancy, self-extinguishing characteristics, electrical insulation ability, high chemical resistance and mechanical properties. One-dimensional (1D)PMIA nanofibers, in particular, are of great interest due to theirunique structures, functionalities, and array of potential applications as protective clothing, high-temperature filters, electrical insulating materials, super capacitors, separators,and structural materials.Recently,electrospinning has been shownto be a simple but powerful technique for the preparation of functional fibrous membranes with nano-and microscale. Also reported is the preparation of electrospun PMIA nanofibers. However, the diameter of these electrospun fibers is usually about150nm, and show randomly oriented nonwoven structure. Generally only the diameter of fibers less than20nm, can the meterials have siginificant nano effect. Meanwhile, the lack of alignment and stretching leading to a relatively low mechanical strength (<40MPa),which significantly limited the practical use of PMIA nanofibers.Firstly, the PMIA and electrospinning was introduced in this thesis. And on the basis of the existing electrospun PMIA fibers, the PMIA nano-fiber/net (NFN)membranes were one-step controllably prepared via electro-spinning/netting (ESN), and the average diameter of nanonet was about15nm.The representative field emission scanning electron microscopy (FE-SEM) as the main analytical tools, the effect of solution concentration, the content of MWCNTs and the process parameter of electrospinning (voltage, relative humidity (RH) and the speed of roller)were analyzed. At the same time the transmission electron microscopy image (TEM) clearly shows that the MWCNTs were embedded well in PMIA nanofiber matrix. The results showed that increasing the solution concentration and the content of MWCNTs were in favour of the formation of PMIA NFN, and the diameter of nanofibers also increased. In addition, when the voltage increased the aperture of NFN was enlarged; Increasing the RH could reduce the formation of NFN, and enhanced the adhesion of nanofibers; And with the speed of roller increased, the mesh showed aligned. In this topic, we inspired from the formation of PMIA NFN, by regulating the RH, the content of LiCl and the speed of roller, we prepared the PMIA fibrous membranes with good alignment. From the FE-SEM and tensile test we found that these three factors all had impact on the degree of orientation and mechanical properties of fibrous membranes. The results showed that increasing the RH and rotate speed could improve the orientation of PMIA nanofiber, so as to improve the mechanical properties of fibous membranes; While increasing the content of LiCl could improve the orientation of fibers, but as the large precipitation of LiCl the tensile strength of fibers decreased. At the base of the aligned PMIA nanofibers, we added different content of MWCNTs in PMIA solution whose concentration was14wt%. In the condition of RH55%and rotate speed200rpm which could produce the best aligned PMIA nanofibers, we prepared the PMIA/MWCNT hybrid nanofibers. By FE-SEM, Raman spectral (2D and3D Raman microscopic imaging), X-ray diffraction (XRD), thermal gravimetric analyzer (TGA) and tensile test, we analyzed the morphology, hierarchical aligned structure, crystal structure, thermal stability and mechanical properties of hybrid nanofibers at different MWCNTs content, respectively. And the results shew that when the content of MWCNTs was less than2wt%, increasing the MWCNTs content could improve the orientation, crystallinity, thermal stability and mechanical properties of hybrid nanofibers. Theas-prepared membranes with MWCNTs contents of1.5wt%exhibited the extreme orientation and high tensile strength of316.7MPa. Moreover, a convincing example showing therobust mechanical strength was presented by the digital photos.