Enhancing Mechanical and Thermal Performance of Injection-Molded PLA via Nucleation and Processing Optimization

Area of Science:

• Materials Science
• Polymer Science
• Chemical Engineering

Background:

• Polylactic acid (PLA) is a biodegradable polymer with limited thermal stability.
• Improving PLA's heat deflection temperature (HDT) is crucial for expanding its applications, particularly in food packaging.

Purpose of the Study:

• To investigate the combined effects of orotic acid (OA) nucleation and injection molding parameters on PLA's crystallization and thermo-mechanical performance.
• To achieve high-crystallinity and high-HDT PLA without requiring post-annealing.

Main Methods:

• Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) to analyze crystallization behavior.
• Mechanical testing (tensile and flexural) to evaluate thermo-mechanical properties.
• Heat deflection temperature (HDT) measurements to assess thermal performance under varying processing conditions.

Main Results:

• 2 wt% OA significantly accelerated PLA crystallization, reaching 52-53% crystallinity under optimized low packing pressure and long hold times.
• Tensile modulus increased with hold time, while tensile strength decreased due to skin layer relaxation.
• Flexural strength increased with packing pressure; flexural modulus decreased with decreasing crystallinity under higher pressure.
• Optimized PLA-OA samples exhibited significantly improved HDT, ranging from 100 °C to 131 °C, compared to the baseline 58 °C.
• Highest HDT values correlated with high crystallinity, extended lamellar development, and strong α-phase formation.

Conclusions:

• Combining OA nucleation with controlled injection molding is an effective strategy to produce high-crystallinity, high-HDT PLA.
• This approach eliminates the need for post-annealing, offering a more efficient route for manufacturing thermally stable PLA.
• The developed PLA-OA materials are suitable for demanding applications like hot-fill and reheatable food packaging.