Correlation between Processing Parameters, Morphology, and Properties of Injection-Molded Polylactid Acid (PLA)...

Area of Science:

• Polymer Science
• Materials Science
• Bioplastics Research

Background:

• Polylactic acid (PLA) is a versatile bioplastic used in packaging, agriculture, and medical devices.
• Understanding PLA's material properties, influenced by processing, is crucial for new applications and recyclability.
• Current research often overlooks local structural inhomogeneities, focusing only on global material properties.

Purpose of the Study:

• To investigate the morphological, thermal, and mechanical properties of injection-molded PLA at both global and local scales.
• To analyze the influence of processing parameters (melt temperature, mold temperature, cooling time) and D-isomer content on PLA's properties.
• To elucidate the relationship between local morphology, crystallization behavior, and the mechanical performance of PLA.

Main Methods:

• Injection molding of PLA tensile bars.
• Morphological, thermal, and mechanical property analysis at different length scales (global and local).
• Micromechanical investigations to correlate local microstructure with failure behavior.

Main Results:

• PLA forms crystalline structures only when cooled in a mold above its glass transition temperature (Tg).
• Lower D-isomer content in PLA leads to a higher degree of crystallinity.
• Mechanical properties from tensile tests did not correlate with overall crystallinity, indicating inhomogeneous morphology.
• Micromechanical analysis revealed a direct link between local morphology and failure behavior within PLA tensile bars.

Conclusions:

• Mold temperature above Tg is essential for PLA crystallization.
• D-isomer content significantly impacts PLA's crystallinity.
• Local structural variations within PLA are critical for understanding its mechanical performance and failure mechanisms, necessitating scale-dependent analysis.