Fabrication And Morphology Development Of Thermoplastic Polymer Nanofibers

Since the 21st century, we have made great advances in nanotechnologies, which stimulated the development of fiber materials science. Polymer nanofibers with diameters less than 1μm have a large range of applications such as soft tissue replacement, filter media materials and reinforced composite materials because of the enormous specific surface. In a broad sense, polymer nanofibers can be prepared using a lot of techniques. Unfortunately, there were small kinds of thermoplastic polymer nanofibers produced by means of no matter which the electrospinning process or the CO2 laser-thinning method. There were three kind of polymer blends investigated in this paper:poly (trimethylene terephthalate)/polylactide (PTT/PLA), isotactic polypropylene/polylactide (iPP/PLA), and polylactide/copolyester (PLA/co-PET). PTT, iPP, PLA nanofibers with averaged diameters less than 500nm were successfully fabricated by blending two components in a co-rotating twin-screw extruder, melt extruding the immiscible blends through a rodlike die, drawing the extrudates through the die, and then selectively removing the matrix from the extrudates.Miscibility, thermal properties and rheological behaviors of PTT/PLA, iPP/PLA, PLA/co-PET blends were investigated using thermogravimetric analyzer (TG), differential scanning calorimeter (DSC), dynamic mechanical analysis (DMA), advanced capillary rheometer and dynamical rheometer. Results indicated that all the blends were thermodynamically immiscible. On increasing the shear rate, the viscosity decreased sequentially, implying that the materials were Non-Newtonian fluids and all followed the shear-thinning behavior. The viscosity ratios ranged from 0.1～10 at the suitable processing temperatures. Particularly, the viscosity ratio of PLA to co-PET was close to one, which indicated that the PLA fibrillar dispersed phase might be obtained after removing the matrix phase.The morphology development trends of dispersed phase at different stages were nearly the same. The dispersed phase underwent the formation of sheets, holes and network structures, then the size reduction and formation of nanofibers. It was clearly that the morphology of PTT, iPP, and PLA nanofibers could be well controlled by the appropriate composition ratios, processing temperatures and drawing ratios and so on. Otherwise, the results of FTIR revealed that there were few specific interactions forming between dispersed phase and matrix phase under the processing conditions.