Ab initio elasticity of poly(lactic acid) crystals

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Poly(lactic acid) (PLA) is a biodegradable polymer with diverse applications.
• Understanding the elastic properties of crystalline PLA is essential for material design.
• Previous studies have explored PLA's mechanical behavior, but detailed first-principles analysis of its crystalline forms is needed.

Purpose of the Study:

• To investigate the elastic properties of different crystalline forms of poly(lactic acid).
• To calculate the stiffness and compliance matrices for poly(l-lactic acid) (PLLA) alpha- and beta-forms, and its stereocomplex (sc).
• To analyze the mechanical anisotropy of crystalline PLA and its contribution to fiber properties.

Main Methods:

• First-principles pseudopotential plane wave method.
• Generalized gradient approximation (GGA) within density functional theory (DFT).
• Finite strain technique for elastic property calculations.
• Cylindrically symmetric polycrystalline aggregate model for fiber analysis.

Main Results:

• Crystalline poly(lactic acid) demonstrates high mechanical anisotropy.
• Elastic constants (stiffness and compliance matrices) were computed for PLLA alpha-, beta-, and sc-forms.
• The study estimated the crystalline phase's contribution to the elastic modulus anisotropy in uniaxially oriented PLA fibers.

Conclusions:

• Crystalline poly(lactic acid) exhibits significant inherent mechanical anisotropy.
• The calculated elastic properties provide fundamental data for predicting and enhancing PLA material performance.
• This research offers insights into the structure-property relationships governing PLA's mechanical behavior.