Cold Crystallization of Glassy Polylactide during Solvent Crazing.

Area of Science:

• Materials Science
• Polymer Science
• Mechanical Engineering

Background:

• Uniaxial tension and polymer chain orientation/crystallization improve mechanical properties.
• Amorphous isotropic polylactide (PLA) is a common polymer with potential for enhanced mechanical performance.

Purpose of the Study:

• To investigate the crystallization of amorphous PLA during film drawing in liquid media.
• To explore the mechanism of solvent crazing-induced crystallization in PLA.

Main Methods:

• Drawing of PLA films in adsorption-active liquid media (ethanol, water-ethanol, n-heptane).
• Analysis of polymer crystallization using solvent crazing mechanism.
• Characterization of crystalline structure and properties via Wide-Angle X-ray Scattering (WAXS).

Main Results:

• Crystallization occurs under simultaneous tensile stress and liquid medium action, independent of the liquid's nature.
• Polymer crystallinity increases with fibrillar material fraction, reaching 42-45% maximum.
• Crystallization happens within crazes involving nanofibrils (10-20 nm diameter), forming α'-crystalline phase (3-5 nm crystallites).
• PLA film strength increased to 200 MPa after stretching in liquid media.

Conclusions:

• Solvent crazing is an effective mechanism for inducing crystallization and enhancing PLA mechanical properties.
• The process leads to significant improvements in tensile strength and material toughness.
• Understanding this mechanism opens avenues for designing high-performance polymer films.