Preparation Of High-Oriented Electrospun Pan Copolymer Nanofibers And Its Relevancy Research

Electrospinning is a direct method to get long nanofibers. The traditional electrospun nanofibers distributed as a non-woven form because of the Taylor cone. These fibers can't get necessary high magnification stretching because of the cross-network structure in the post-treatment process of the precursor and the preparation of carbon fiber. They also can't meet the demands of high degree of oriented PAN macromolecules with carbon net level.It makes the mechanical properties of the electrospun nanofibers are low and can't be used for structural materials for a long time. Therefore, explore works of collecting high-oriented electrospun nanofibers along the axial in electrospinning areas became hot research at home and abroad.As the water is a good conductor of electricity, and carbon fiber precursor need further removal of residual solvents and get necessary high magnification stretching in water in the follow-up processes.Combined with wet spinning process, a new way of continuous flow water bath collection was designed and established in this subject to get high-oriented long electrospun nanofibers along the axial.Voltage, collection distance and speed of the roller on nanofibers' morphology and structure were studied in this subject.The essential conditions of this experiment were identified. Structures and properties of electrospun PAN nanofibers collected from two different methods including water flow and rotational device were studied, and the results were compared to those acquired from the conventional PAN microfibers (SAF 3K provided by the Courtaulds, Ltd in the UK) by Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD) and Scanning electron microscope(SEM). The influence of the water bath temperature on the nanofiber collection method of water flow was also studied in this paper. The process of stretching was researched in this article. The process of stretching was therefore required to improve the structures and properties of electrospun nanofibers.The differences of the nanofibers in structures and properties before and after stretching were studied and this paper also compared the structures and properties of electrospun PAN nanofibers collected from two different methods after the same stretching process.The results showed that (1) Compared with the traditional fibers, the electrospun nanofibers had smaller diameter and fewer surface defects, and basically there were no grooves on the surface of the fiber; (2) Electrospinning PAN precursor had two peaks in air in the DSC diagram;(3) Electrospun nanofibers'orientation degree and crystallinity were 55.0%,42.8% and they were smaller than the SAF 3K provided by the Courtaulds which had been stretched about eight times(83.0%,77.46%). But compared with the electrospun PAN nanofibers collected from rotational device in the same rotational speed(51.1%,5.7%), electrospun PAN nanofibers collected from water flow had higher degree of crystallinity and orientation. (4) residual solvent rate of electrospun PAN nanofibers collected from water flow was only 1.34% that was lower than the nanofibers collected from rotational device which was 3.87%.(5) Surface roughness of nanofibers collected from water flow was mainly affected by voltage, concentration, collection distance, ambient temperature, cleanliness of bath collection, and other factors.(6)The lower water bath temperature can more easily obtain fiber with smooth surface and lower residual solvent. The higher water bath temperature the fiber was rougher and had more defects on the surface. With the water bath temperature rising, the fibers'density decreased, the diameter increased and crystallinity decreased.(7) The process of stretching was therefore required to improve the structures and properties of electrospun nanofibers; and the stretching process led to substantial improvements of macromolecular orientation and crystallinity.(8) Electrospun PAN nanofibers collected from water flow decreased nearly 40% in diameter after 3 times drawing, while nanofibers collected from rotational device decreased only 17%. Crystallinity and orientation degree of nanofibers collected from water flow increased 67.87% and 63.09%, and orientation degree of nanofibers collected from water flow was 89.7% which was higher than the Courtauld fibers'. DSC enthalpy of the nanofibers collected from water flow was more than nanofibers collected from rotational device.