PLLA/PVA Composite Nanofibers By Electrospinning

As a new kind of environment-protection materials, poly( L-lactic acid ) (PLLA) has a wide application in medicine, industry, national protection, et al, especiallly when it is combined with the technology of electrospinning. But the poor hydrophilicity, low speed of degradation have a bad effect on its application. In this article, poly(vinly alcohol) (PVA) was used to improve PLLA. PLLA/PVA blended or composite micro/nanofibers were prepared by the means of electrospinning. The spinning effect and fibers'properties were analyzed by apparatuses.Firstly, PLLA/PVA composite nanofibers were prepared with the self-assembled electrospinning equipment, in which two kinds of solutions were blended as the spinning solution. The proper technical parameters, which were determined by video zoom microscope and atomic force microscope (AFM), were as follows: 14%/6% of the concentration ratio of PLLA/PVA, 12kV of the spinning voltage, 0.5mL/h of the extruding speed, 18cm of the collecting distance. Well-shaped fibers were obtained with these parameters. Some chemical interaction between PLLA and PVA in the blended fiber had been proved by infrared spectrum (IR) . The incompatibility of PLLA and PVA in the nanofibers was observed using tapping and phase modes of AFM. But there were great differences among nanofibers prepared in different time. More droplets and beads appeared in the latter case. It may be caused by the change of environment and material properties. Because of the unstability of the spinning result, it couldn't repeated, other preparation method of PLLA/PVA composite nanofibers was taken.A twin-spinneret electrospinning equipment, which had two sets of solution-extruding devices and high-voltage power supplies and a roller as the co-collecting device, was set up and the PLLA/PVA composite micro/nanofibers had been prepared with two kinds of solutions spinning separatedly. After analyzing the images of video zoom microscope and scanning electron microscope (SEM), the most suitable technical parameters were listed as follows: PLLA solution, concentration 30%, voltage 15kV, extruding speed 1.0, 0.8, 0.5, 0.2mL/h, collecting distance 15cm; PVA solution, concentration 10%, voltage 18kV, extruding speed 0.2mL/h, collecting distance 15cm; rotating speed of the roller 200r/min. And the structure, diameter distribution and surface roughness of nanofibers were analyzed by SEM and AFM. The mechanical property of composite nanofiber mats was analyzed by tension test and force-distance curves. PLLA 1.0mL/h showed the best mechanical property and PLLA 0.5mL/h was the worst. PLLA got a better adhesive ability than PVA did. Composite nanofiber mats had a great improvement on the wettability comparing with the pure PLLA nanofiber mat, which was proved by the tests of static contact angle and dynamic water adsorption. PLLA 0.2mL/h was the best. Some improvements on the thermal stability of PLLA had been made with PVA added.