Monitoring Antioxidant Consumption and Build-Up in Polypropylene During Open-Loop and Closed-Loop Mechanical...

Area of Science:

• Polymer Science
• Materials Science
• Chemical Engineering

Background:

• Polypropylene (PP) is susceptible to thermo-oxidative degradation during high-temperature processing.
• Antioxidants (AOs) are crucial for stabilizing PP, but their optimal quantity is critical to avoid inadequate stabilization or safety issues from excessive build-up.
• Recycled PP often contains unpredictable contaminants that can accelerate degradation.

Purpose of the Study:

• To present a modified Differential Scanning Calorimetry (DSC) method for measuring Oxidation Induction Temperature (OIT) in recycled PP.
• To ensure the safety of DSC measurements by limiting oxidation and volatile compound release.
• To correlate OIT measurements with residual intact antioxidant (AO) levels in recycled PP.

Main Methods:

• A modified DSC approach was developed to measure OIT in recycled PP, including contaminated samples.
• Measurements were performed in inert environments to ensure safety and prevent volatile compound release.
• The OIT was correlated with residual AO levels in both open- and closed-loop recycled rigid PP.

Main Results:

• The modified DSC method provides a safe and effective way to measure OIT and infer residual AO levels.
• Recycled PP from open-loop systems retains sufficient residual AOs for limited thermal reprocessing, despite contamination.
• Closed-loop recycling with added AOs in each cycle leads to significant AO build-up, maintaining PP homogeneity.

Conclusions:

• The developed OIT measurement technique is valuable for monitoring AO levels in recycled PP.
• Open-loop recycled PP possesses adequate AO for some reprocessing, while closed-loop recycling requires careful AO management to prevent over-accumulation.
• The study highlights the importance of AO monitoring in sustainable plastic recycling strategies.