Complex Morphology Formation in Electrospinning of Binary and Ternary Poly(lactic acid) Solutions

Electrospinning of ternary systems containing a nonsolvent is of interest because it can produce fibers that are highly porous on the surface and in the core. Despite the growing interest and applications, electrospinning of such ternary systems is challenging due to their evolving viscoelastic properties prior to electrospinning. In this study, we produce porous/rough poly(lactic acid) (PLA) fibers via electrospinning of binary and ternary systems of PLA, dichloromethane (solvent) and hexane (nonsolvent). We introduce a rheological approach to determine the appropriate time for electrospinning of ternary systems which is within at most 10% of their induction time of crystallization, when incipient crystals are formed within the polymer-rich phase. These incipient crystals act as nucleators for further crystallization during the process leading to higher crystallinity and more α form crystals. Surprisingly, the pore morphology and crystallinity of the as-electrospun fibers are drastically changed after a room temperature solvent exchange. During this process, cold crystallization and α′ to α recrystallization occur for all systems. Also, the surface porosity of the fibers is decreased after the solvent exchange, except for the fibers produced from the ternary systems with higher PLA concentrations. Our results indicate that the crystallinity and surface texture of electrospun membranes and thus their performance may change during subsequent analysis and in-service applications, even when a highly volatile solvent is used as a spinning medium.