Polypropylene Degradation on Co-Rotating Twin-Screw Extruders

Area of Science:

• Polymer Science and Engineering
• Materials Processing and Compounding

Background:

• Compounding additives into base polymers is crucial for creating usable plastic materials with specific properties.
• Co-rotating twin-screw extruders are commonly used for polymer compounding, but process-induced thermal and mechanical stress can cause irreversible material degradation.
• Previous studies at Kunststofftechnik Paderborn have modeled polypropylene (PP) degradation on a 28 mm twin-screw extruder.

Purpose of the Study:

• To experimentally investigate the transferability of existing polypropylene degradation models to different machine sizes (25 mm and 45 mm extruders).
• To evaluate the degradation behavior of polypropylene compounds containing titanium dioxide and carbon fibers.
• To validate and adapt a previously developed material degradation calculation model for broader applicability.

Main Methods:

• Processing of pure polypropylene on 25 mm and 45 mm screw diameter extruders.
• Processing of polypropylene compounds (with titanium dioxide and carbon fibers) on a 28 mm extruder.
• Measurement of melt flow rates (MFR) for pure PP and calculation of molar masses.
• Analysis of compounds using gel permeation chromatography (GPC).

Main Results:

• High rotational speeds, low throughputs, and high melt temperatures consistently lead to increased material degradation, consistent with prior findings.
• The previously developed material degradation model can predict degradation across different machine sizes with adjusted process coefficients.
• The study provides insights into the degradation behavior of PP when compounded with additives like titanium dioxide and carbon fibers.

Conclusions:

• The material degradation model for polypropylene is transferable to different extruder sizes, enabling broader application.
• Compounders can utilize the provided recommendations and calculation model to design material-gentle processes for polypropylene, regardless of machine size.
• Optimizing processing parameters is key to minimizing irreversible damage and maintaining polymer properties during compounding.