Structural study of poly(L-lactic acid) spherulites.

Area of Science:

• Polymer Science
• Materials Science
• Crystallography

Background:

• Poly(L-lactic acid) (PLLA) is a biodegradable polymer with potential applications in various fields.
• Understanding the crystalline structure of PLLA and its blends is crucial for tailoring material properties.
• Atactic poly(3-hydroxybutyrate) (a-PHB) is another biopolymer whose blends with PLLA can modify material characteristics.

Purpose of the Study:

• To investigate the structural changes in PLLA spherulites upon blending with a-PHB.
• To analyze the orientation and periodicity of unit cells within PLLA/a-PHB blends using advanced X-ray diffraction techniques.
• To correlate X-ray diffraction findings with optical microscopy observations.

Main Methods:

• Microfocus X-ray diffraction using synchrotron radiation was employed.
• Radial scans with a small beam diameter were performed on PLLA and PLLA/a-PHB blends.
• Polarized optical microscopy was used for comparative analysis.

Main Results:

• In pure PLLA, the unit cell a-axis showed radial orientation, while other axes were randomly oriented.
• PLLA/a-PHB blends exhibited periodic changes in diffraction patterns with increasing distance from the spherulite center.
• The a-axis consistently aligned radially, with b- and c-axes rotating around 'a' at a frequency that increased with a-PHB content.
• X-ray reflection broadening indicated structural disorder increasing with a-PHB concentration.

Conclusions:

• The addition of a-PHB to PLLA significantly alters the crystalline structure of spherulites.
• A distinct helical twisting of the PLLA unit cell occurs in the presence of a-PHB, with the twisting frequency dependent on a-PHB content.
• These structural modifications correlate with macroscopic observations and impact the material's properties.