Influence of precursor solvent and confined environment on the polymorphic transition in electrospun Poly(L-lactide) fibers

The present study examined the thermal and crystallization properties of poly(L-lactide) (PLLA) chains confined in electrospun fibers. The heat of fusion and crystallite sizes decreased with a decrease in fiber diameter because of the confinement effect. The crystal structure of PLLA fibers exhibited alpha ' and alpha forms, which comprised loosely and closely packed chains, respectively. As-electrospun PLLA fibers exhibited an unstable alpha ' phase because of the rapid solidification of polymer chains during electrospinning. Subsequent thermal annealing at a temperature higher than 140 degrees C induced a polymorphic transition from the alpha ' phase to the stable alpha phase. This finding differed from that observed in bulk PLLA, which exhibited alpha crystals regardless of annealing temperature. Furthermore, the polymorphic transition of alpha ' crystals to alpha crystals in fibers fabricated with 95:5 chloroform/trifluoroethanol solvent occurred with lower annealing temperatures or shorter annealing times relative to those fabricated with 60:40 chloroform/trifluoroethanol solvent. This behavior was attributed to the low entanglement content in the PLLA chains in fibers fabricated with 95:5 chloroform/trifluoroethanol solvent; the low entanglement content increased chain mobility, thereby accelerating polymorphic transition.

Automated summary

The study investigated the thermal and crystallization properties of PLLA chains confined in electrospun fibers, revealing that crystal structure and phase transition were influenced by fiber diameter and annealing temperature. Low entanglement content in PLLA chains in fibers fabricated with 95:5 chloroform/trifluoroethanol solvent resulted in faster polymorphic transition compared to fibers fabricated with 60:40 chloroform/trifluoroethanol solvent.