Mechanical Enhancement of Biaxially Cold Rolled Poly (L‐Lactic Acid): Influence of Crystallinity and Short‐Term Physical Aging

Amorphous and semicrystalline PLLA plaques were biaxially rolled at room temperature and characterized over 2 weeks to assess changes in their tensile, flexural, and impact properties. Results demonstrate that rolling induces a brittle‐to‐ductile transition, significantly enhancing mechanical toughness across all measured parameters. Amorphous PLLA exhibited a 600% increase in tensile toughness that diminished to control values 6 days after rolling, while maintaining a 270% increase in flexural toughness and a 45% increase in impact strength. In contrast, low crystallinity PLLA (37% ± 1%) demonstrated a stable 1350% and 430% increase in tensile and flexural toughness, respectively, after rolling. Moderate crystallinity PLLA (46% ± 6%) demonstrated a 290% increase in tensile toughness and up to a 140% increase in impact strength after rolling. The degree of crystallinity and applied force direction were found to be critical factors in determining the deformation mechanism and aging behavior. This work demonstrates that biaxial cold rolling offers an environmentally friendly alternative to chemical modifications for enhancing the mechanical properties of PLLA, providing tunable property improvements based on crystallinity and rolling parameters that can expand the applications of this biodegradable polymer in packaging, agriculture, and biomedical fields.