Degradation of Polypropylene and Polypropylene Compounds on Co-Rotating Twin-Screw Extruders

Area of Science:

• Polymer Science
• Materials Engineering
• Chemical Engineering

Background:

• Polypropylene (PP) undergoes degradation from thermal, mechanical, and oxygen exposure during twin-screw extrusion.
• Previous mathematical models predicted PP degradation but required adjustments for different extruder sizes.
• Filled PP compounds present unique challenges due to altered thermodynamic and rheological properties.

Purpose of the Study:

• To modify and validate a mathematical model for predicting polypropylene degradation during twin-screw extrusion.
• To investigate the degradation behavior of filled PP compounds (PP/TiO2).
• To assess the model's applicability to filled PP compounds and identify discrepancies.

Main Methods:

• Processing of neat PP and PP/TiO2 compounds using a co-rotating twin-screw extruder under varied operating parameters.
• Determination of polymer degradation via melt flow rate (MFR) and gel permeation chromatography (GPC) measurements.
• Modification of a pre-existing mathematical model by adjusting sensitivity parameters for extruder size independence.

Main Results:

• Increased temperatures, screw speeds, and decreased throughputs generally led to higher PP degradation, consistent with prior research.
• The modified model accurately predicted degradation for neat PP across different extruder sizes.
• The model showed poor agreement with measured degradation for PP/TiO2 compounds, indicating altered degradation mechanisms.

Conclusions:

• The developed mathematical model effectively predicts polypropylene degradation, independent of extruder size.
• The presence of fillers (TiO2) significantly alters the thermodynamic and rheological properties of PP, impacting its degradation behavior.
• Further model refinement is necessary to accurately capture the degradation of filled polymer compounds.