Solvent selection and its effect on crystallization behavior of poly(ε-caprolactone) in electrospun poly(ε-caprolactone)/poly (lactic-co-glycolic acid) blend fibers

Biodegradable poly(ε-caprolactone) (PCL) and poly(lactic-co-glycolic acid) (PLGA) are both significant members of polyester family. In addition to their immense potential as tissue engineering scaffolds, disposable or short-lived biomedical materials could be also designed based on PCL/PLGA blends. The environmental degradation of such low-cost polyester-based blends strongly depend on the crystallization behavior and the crystal morphology of semicrystalline PCL component that correlate to the processing conditions of the blends. In this study, electrospinning, a non-equilibrium laboratory processing condition, was utilized to prepare 80:20 by mass PCL/PLGA blend fibers. Morphological study and thermal analysis were performed to study the crystallization behavior of PCL in the electrospun PCL/PLGA blends prepared using different solvents: chloroform (CHCl3), 2,2,2-trifluoroethanol (TFE), and CHCl3/TFE 1:1 vol mixture. PCL/PLGA fibers prepared using TFE or CHCl3/TFE solvents are significantly thinner than those prepared using CHCl3 solvent. The difference in the glass transition temperature PCL among these fibers is negligible, implying the poor miscibility of the 80:20 by wt. PCL/PLGA blend regardless of the solvent selected, due presumably to the relatively high PCL concentration. After removing PLGA phase using acetone, microscopic scale phase separation morphology was observed for thicker PCL/PLGA fibers (prepared using CHCl3 solvent). In contrast, for the thinner fibers (prepared using CHCl3/TFE mixture solvent), failure occurs and fibers broke cross-sectionally after acetone wash. Solvent vapor annealing experiment further unveiled the PCL lamellar network in the thicker fibers and the PCL shish-kebab in the thinner fibers, suggesting that for immiscible blends, the PCL crystallization mechanism strongly depends on the non-equilibrium laboratory processing conditions and less depends on the molecular characteristics of the second component.