Differential scanning calorimetry study on thermal behaviors of freeze-dried poly(L-lactide) from dilute solutions

Differential scanning calorimetry study on thermal behaviors of freeze-dried poly(L-lactide) from dilute solutions
Published Online: 18 Nov 2004
Received: 8 June 2004; Revised: 31 August 2004; Accepted: 29 September 2004
Takashi Sasaki *, Nobutaka Yamauchi, Satoshi Irie, Kensuke Sakurai
Journal of Polymer Science Part B: Polymer Physics
Volume 43, Issue 2 , Pages 115 - 124
Wiley InterScience
Department of Materials Science & Engineering, Fukui University, Fukui 910 8507, Japan

email: Takashi Sasaki (sasaki@matse.fukui-u.ac.jp)
*Correspondence to Takashi Sasaki, Department of Materials Science & Engineering, Fukui University, Fukui 910 8507, Japan
Keywords
freeze-dried ? poly(L-lactide) ? glass transition ? crystallization ? melting ? step-scan ? DSC ? mobility
Abstract
Glass transition, cold crystallization, and melting of freeze-dried poly(L-lactide) (PLLA) prepared from dilute 1,4-dioxane solutions were investigated by differential scanning calorimetry (DSC). Conventional DSC measurements of heating scans revealed that freeze-dried PLLA prepared from a 0.07 wt % solution undergoes a two-step cold crystallization (or reorganization) with a lower exotherm appearing at about 78 ?C and with a higher broad exotherm between 110-155 ?C. The peak temperature of the former exotherm is about 50 K lower than that observed for a reference bulk sample. Step-scan mode DSC, which provides information essentially equivalent to that obtained from the temperature-modulated DSC, revealed that the glass-transition temperature is about 6 K lower than that of the reference bulk. These findings suggest enhanced chain mobility for freeze-dried PLLA. Freeze-dried PLLA that crystallized at 80 ?C for 40 min was revealed to contain a rather large amount of rigid amorphous material (42%). ? 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 115-124, 2005
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