Lamellae assembly in dendritic Spherulites of Poly(L-lactic Acid) crystallized with poly(p-Vinyl Phenol)

Siti Nurkhamidah, Eamor M. Woo*, Yu Ting Yeh, Faliang Luo, Vimal Katiyar

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)

Abstract

Lamellar assembly with fractal-patterned growth into dendritic and ringed spherulites of crystallized poly(L-lactic acid) (PLLA), of two molecular weight (MW) grades and crystallized at (temperature of crystallization) Tc = 120 and 130 °C, respectively, are evaluated using optical and atomic-force microscopies. The results of surface-relief patterns in correlation with interior microscopy analyses in this work strongly indicate that the observed birefringence changes in PLLA polymer dendritic or ringed spherulites (from blue to orange, or to optical extinction) need not be definitely associated with the continuous helix twisting of lamellae; they can be caused by sudden and discontinuous lamellae branching at intersected angles with respect to the original main lamellae, as proven in the case of dendritic and zig-zag rough-ringed spherulites. Intersection angles between the main stalks and branches tend to be governed by polymer crystal lattices; for PLLA, the orthorhombic lattice (α-form) usually gives a 60° angle of branching and hexagonal growth. The branching lamellae then further bend to convex or concave shapes and finally make a 60-90° angle with respect to the main stalks. Such mechanisms are proven to exist in the straight dendritic/striped high-molecular weight (HMW)-PLLA spherulites (Tc = 120 °C); similar mechanisms also work in circularly ringed (Tc = 130 °C) HMW-PLLA spherulites.

Original languageEnglish
Article number545
JournalPolymers
Volume10
Issue number5
DOIs
Publication statusPublished - 18 May 2018

Keywords

  • Birefringence
  • Dendrites
  • Poly(L-lactic acid)
  • Ringed spherulites

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