Controllable Fabrication And Applications Of Electrospun PMIA Nanofibers

Poly(m-phenylene isophthalamide)(PMIA), one of the most important aromatic polyamides,has been widely used as protective clothing, high-temperature filters, electrical insulating materials,and structural materials due to its excellent prominent thermostability, high flame retardancy, self-extinguishing characteristics, electrical insulation ability, high chemical resistance and mechanicalproperties. With the increasing requirement of high temperature resistance fiber, PMIA fiber is fullydeveloped. At present, the diameter of PMIA fiber are generally for micron level, usually used as astructural material. PMIA nanofibers have more excellent performance,(such as small diameter,pore size and large specific surface area, high porosity), which can greatly expand the applicationfields of the PMIA. However, the fabrication of PMIA nanofibers is still difficult, which does limitthe further development of the PMIA fiber. As the only direct as well as the most saving way thatcan prepare nanofibers, the electrospinning has got more and more attention in recent years. Moreand more people focus on it due to its wide applications. And many papers about the fabrication ofelectrospun PMIA nanofibers have been reported. However, most of the studies only simplyresearched the morphology and structure of the PMIA fibers. Little of the study are about thepractical application. The study of the PMIA fiber still remain drawbacks, such as the highprocessing requirements, small scale, low mechanical strength. So, it’s important to further studythe application of the PMIA fiber.Firstly, the PMIA and electrospinning was introduced in this thesis. By studing the structureregulation, we further studing the big-scale high aligned nanofibers and nanonets air filtrationnanofibers.Creating a facile and efficient method that can provide large-scale, highly aligned, and highstrength nanofibers has proved extremely challenging. This work responds to these challenges by designing and evaluating PMIA nanofibrous materials with robust tensile strength, which can befabricated on a large scale via a facile combination of relative humidity (RH)-regulatedelectrospinnig and multi-level aggregates reconstructing. The morphology and structure of PMIAmembranes can be finely controlled by regulating the solution concentration and RH duringspinning, and a possible RH-regulated aligning mechanism was proposed. Additionally, PMIAnanofibrous aggregates of yarns and subsequent plaits were built up by multi-level reconstructing.During the first-level reconstructing based on twisting, the structure and mechanical property of theyarns can be facilely optimized by tuning the twist level, and the PMIA yarns with3000TPMpossess robust tensile strength of262MPa. The second-level reconstructing based on yarns braidingendows the corresponding nano-plaits with the highest tensile strength of330MPa.In this study, we inspired from the formation of aligned PMIA nanofibers, by regulating theconcentration of PMIA, the RH and the concent of the N,N,N-trimethyl-1-dodecanaminiumbromide (DTAB), we prepared the PMIA fibrous membranes with nanonets for air filtration. Themorphology of as-spun nanofibrous membranes were characterized by using FE-SEM. The filtrationperformance and the mechanical properties on the structure and morphology of PMIA fibrousmembranes were characterized. We found that, the optimum concentration of PMIA (12wt%) wasused for detailed investigation. When the RH reduced to25%, there are nano-neting in the PMIAfibrous membranes. And This structure can improve the efficiency of the air filtration. At last, inorder to improve the content of the nannets, we increase the content of the DTAB. When theconcentratin of DTAB attach to0.15wt%, the fibrous membrane have the highest specific surfacearea26.9m2/g. At the same time, the filtration performance and the mechanical properties of themembranes is the best. According to the environment requirements, we chose different weights offibrous membranes. When the fibrous membrane have weight about0.37g/m2, the filtrationefficiency of aerosol particles of dust (0.3~0.5μm) was99.999%, The pressure drop was only95Pa (air flow rate of32L/min).