Role of Shear Flow on Structure Development during Post-Processing Annealing for Poly(lactic acid).

Area of Science:

• Polymer Science
• Materials Science
• Crystallization Kinetics

Background:

• Poly(lactic acid) (PLA) exhibits a low crystallization rate, making as-processed films typically amorphous.
• Lack of inherent crystallinity and molecular orientation in quenched PLA films limits their mechanical properties.

Purpose of the Study:

• To investigate the influence of shear history on the structural evolution of PLA during post-processing annealing.
• To understand the mechanism of crystal growth and molecular orientation induced by annealing in previously sheared PLA.

Main Methods:

• Processing of poly(lactic acid) films with controlled shear history.
• Annealing the films above their glass transition temperature.
• Characterization of crystallinity and molecular orientation using structural analysis techniques.

Main Results:

• Quenched PLA films without shear history showed no crystallinity or molecular orientation.
• PLA films with appropriate shear history exhibited significant molecular orientation and crystallization upon annealing.
• Annealing-induced crystallization was attributed to the formation of extended chain crystals during the shear process.

Conclusions:

• Shear history is a critical factor in controlling structure development in PLA during annealing.
• The study demonstrates a method to induce molecular orientation and enhance crystallinity in PLA through controlled processing and annealing.
• This phenomenon offers potential for improving dimensional stability and rigidity in PLA-based products.