Stretching-induced crystallinity and orientation of polylactic acid nanofibers with improved mechanical properties using an electrically charged rotating viscoelastic jet

An electrospinning technique with an additional centrifugal field was employed to prepare polylactic acid (PLA) nanofibers. The results indicated that combining the strong stretching force of the additional centrifugal field and an electrostatic field can align the PLA polymer chains parallel to the nanofiber axis, producing PLA nanofibers with superior crystalline features, molecular orientation and conformation as well as good mechanical properties. The optimal stretching force for an electrically charged rotating viscoelastic jet was determined by high-speed videography and the analysis of dimensionless groups (i.e., the Re, We, and Oh numbers). The elastic modulus of PLA nanofibers with a crystallinity degree of 37% and a dichroic ratio (D) of 1.89 was measured at 2.64 GPa and 3.30 GPa by atomic-force microscopy (AFM) and nanoindenter experiments, respectively. Furthermore, the optimal PLA nanofibers produced by the proposed method can potentially be applied for the reinforcement of composites.