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 exhibite...

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Bibliographic Details
Published in:Polymer (Guilford) 2021-12, Vol.237, p.124339, Article 124339
Main Authors: Lee, Kuan-Hsuan, Huang, Hsiu-Feng, Lo, Chieh-Tsung
Format: Article
Language:English
Subjects:
Annealing
Chain entanglement
Chain mobility
Chloroform
Confined spaces
Crystal structure
Crystallites
Crystallization
Crystals
Electrospinning
Entanglement
Fiber
Fibers
Heat of fusion
PLLA
Poly(L-lactide)
Polylactic acid
Polymers
Polymorphic transition
Rapid solidification
Solvents
Trifluoroethanol
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Summary: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 α′ and α forms, which comprised loosely and closely packed chains, respectively. As-electrospun PLLA fibers exhibited an unstable α′ phase because of the rapid solidification of polymer chains during electrospinning. Subsequent thermal annealing at a temperature higher than 140 °C induced a polymorphic transition from the α′ phase to the stable α phase. This finding differed from that observed in bulk PLLA, which exhibited α crystals regardless of annealing temperature. Furthermore, the polymorphic transition of α′ crystals to α 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. [Display omitted] •Greater trans−trans conformation was observed in electrospun fibers.•The heat of fusion and crystallite sizes decreased with a decrease in PLLA fibers.•The polymorphic transition depended on the solvent used for preparing fibers.•Good solvents for electrospinning accelerated the polymorphic transition of PLLA.
ISSN:0032-3861
1873-2291
DOI:10.1016/j.polymer.2021.124339