Syndiotactic Polypropylene Nanofibers Fabricated by a Solution Electrospinning Method with Single Solvent at Ambient Temperature

摘要

Solution electrospinning is one of feasible ways to produce fibers ranging from tens of nanometers to several micrometers in diameter. In the solution electrospinning, the polymer solution is ejected from a capillary tip by a strong electrostatic force and deposited onto a collector as fine fibers. The process has been widely employed for numerous polymer/solvent systems to fabricate nanofibers by selecting a good solvent that could most effectively increase the intrinsic viscosity at the same concentration.1 The process has recently been mainly limited to non-crystalline polymers. Polyolefins such as polypropylene (PP) and polyethylene (PE) are semi-crystalline polymers which have unique properties including good mechanical properties and excellent chemical resistance. Such good chemical resistance leads to severe difficulty in dissolving polyolefins into common solvents at ambient temperature. To avoid this, the dissolution of the polyolefins into solvents was generally conducted at elevated temperature. However, by cooling down to ambient temperature, the solution occasionally forms thermoreversible physical gels (behave solid state) due to the nature of the semi-crystalline polymers that work as physical crosslinks. Due to the gelation difficulties, polyolefins were normally spun into fibers by different ways such as melt-electrospinning methods, CO2 laser supersonic multi-drawing, or high-temperature solution electrospinning. Lyons et al. systematically studied the effects of processing conditions on electrospun PP fibers from its melt and found that the average diameters of the synthesized PP fibers were above micron.2 Lee et al. reported that sPP fibers with the average diameter of 650 nm were successfully prepared at slightly elevated temperature (35oC) using a multi-component solvent system composed of cyclohexane, acetone, and DMF.3 Suzuki et al. proposed a novel method for the production of nano-sheets with a carbon dioxide laser by drawing them at supersonic velocities, and they eventually obtained nanofibers with an average diameter of 350 nm.4 In this work, we succeeded in fabricating sPP nanofibers by using a single-solvent electrospinning method at room temperature (25oC).