Correlation between Processing Parameters and Degradation of Different Polylactide Grades during Twin-Screw Extrusion

Area of Science:

• Polymer Science
• Materials Engineering
• Chemical Processing

Background:

• Polylactide (PLA) is a biodegradable polyester with growing applications.
• Understanding the impact of processing parameters on PLA's properties is crucial for its effective utilization.
• Oxidative and thermomechanical degradation can compromise PLA's performance.

Purpose of the Study:

• To investigate the effect of twin-screw extrusion parameters on PLA structure and properties.
• To identify critical processing parameters influencing PLA degradation.
• To evaluate the impact of degradation on PLA quality, focusing on discoloration and molecular weight changes.

Main Methods:

• Twin-screw extrusion processing.
• Fourier-transform infrared spectroscopy (FT-IR) for structural analysis.
• Oscillatory rheological analysis to assess melt properties.
• Differential scanning calorimetry (DSC) for thermal analysis.
• Color analysis on the CIELab scale to quantify discoloration.

Main Results:

• High processing temperatures and shear conditions can induce degradation in PLA.
• PLA grades with a high mass flow index (MFI) and low viscosity exhibit reduced residence time in the extruder.
• Shorter residence time effectively limits discoloration and molecular weight reduction.
• Initial molecular weight is less critical than MFI for mitigating degradation during melt mixing.

Conclusions:

• Optimizing PLA processing involves selecting grades with appropriate melt flow characteristics.
• High MFI and low viscosity are key to minimizing degradation during high-temperature extrusion.
• Processing parameters significantly influence PLA's structural integrity and aesthetic properties.