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Research Papers

Effect of Film Formation Method and Annealing on Morphology and Crystal Structure of Poly(L-Lactic Acid) Films

[+] Author and Article Information
Shan-Ting Hsu

Department of Mechanical Engineering,
Columbia University,
New York, NY 10027
e-mail: sh@caa.columbia.edu

Y. Lawrence Yao

Department of Mechanical Engineering,
Columbia University,
New York, NY 10027
e-mail: yly1@columbia.edu

Manuscript received February 7, 2011; final manuscript received October 25, 2013; published online January 10, 2014. Assoc. Editor: Yong Huang.

J. Manuf. Sci. Eng 136(2), 021006 (Jan 10, 2014) (9 pages) Paper No: MANU-11-1038; doi: 10.1115/1.4025909 History: Received February 07, 2011; Revised October 25, 2013

The poly(L-lactic acid) (PLLA) has potential medical usage such as drug delivery since it can degrade into bioabsorbable products in physiological environments, while the degradation is affected by its crystallites. In this paper, the effects of film formation method and annealing on the crystallites formed in PLLA films are investigated. The films are made through solvent casting and spin coating, and subsequent annealing is conducted. The resulting morphology, molecular order, conformation, and intermolecular interaction are examined using optical microscopy, wide-angle X-ray diffraction, and Fourier transform infrared spectroscopy. It is observed that solvent casting produces category 1 spherulites while annealing the spin coated films leads to spherulites of category 2. The crystal structure of the two kinds of films also shows distinct features. The results enable better understanding of the crystallites in PLLA, which is essential for its medical application.

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Figures

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Fig. 1

(a) The morphology of solvent cast film annealed at 140 °C for 3 h. The morphology is similar to that of the as cast film. (b) The morphology of spin coated film annealed at 140 °C for 3 h. The eye structure is observed.

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Fig. 2

The morphology of spin coated film annealed at 140 °C for 24 h. Eye structure remains observable while the boundary of spherulites can be more clearly observed. The spherical symmetry does not extend to the center, and the sheaf-like features are preserved.

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Fig. 3

(a) Sketch of the lamellar structure in solvent cast films. (b) Sketch of the lamellar structure in spin coated films.

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Fig. 4

(a) WAXD profiles for solvent cast films annealed at different temperatures for 3 h. Dotted line under the as cast film is the fitted curve for the amorphous region. (b) WAXD profiles for spin coated films annealed at different temperatures for 3 h. Dotted line under the 80 °C annealed film is the fitted curve for the amorphous region.

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Fig. 5

Intensity ratio I(110)/(200)/I(203) of the solvent cast and spin coated films annealed for 3 h. The error bar represents the standard deviation.

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Fig. 6

Location of the (110)/(200) peak for the solvent cast and spin coated films annealed for 3 h. The error bar represents the standard deviation.

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Fig. 7

Degree of crystallinity of the solvent cast and spin coated films annealed for 3 h. Annealing temperature of 25 °C means the as cast film. The error bar represents the standard deviation.

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Fig. 8

Degree of crystallinity and peak location of the spin coated films annealed at 140 °C for 1, 3, 8, and 24 h.

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Fig. 9

(a) FTIR spectra of the solvent cast films before annealing and after annealed in different conditions. (b) FTIR spectra of the spin coated films before annealing and after annealed in different conditions.

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Fig. 10

(a) Curve fitting for the gt and tt conformers in the carbonyl C=O stretching region of the as cast solvent cast film. (b) Curve fitting for the gt and tt conformers in the carbonyl C=O stretching region of the solvent cast film annealed at 140 °C for 3 h.

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Fig. 11

Carbonyl C=O stretching region of the spin coated films annealed at different temperatures for 3 h.

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Fig. 12

Second derivative spectra of the C=O stretching region for solvent cast and spin coated films before annealing and annealed at different temperatures for 3 h.

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Fig. 13

Peak width of the resolved spectra for the gt and tt conformers of solvent cast films before annealing and after annealed in different conditions. The error bar represents the standard deviation of the five measurements.

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