Extrusion Rheology vs Standard Rheometers – An Overview

This webinar provides a comprehensive comparison of extrusion-based rheology and conventional rotational rheometry for characterizing thermoplastic polymer flows. The current ASTM D5422 standard employs round capillary die heads in extrusion systems to measure shear viscosity at processing-relevant rates. Recent adaptations incorporate slot capillary dies, enabling accurate viscosity determination at lower shear rates (down to 0.1 s⁻¹) without Bagley entrance corrections, thus simplifying data interpretation and enhancing precision for low-viscosity or shear-sensitive materials.

A new addition is the dual- or three-stage slot capillary die, which simultaneously yields shear viscosity and elongational viscosity from a single extrusion run. This innovation captures extensional flow behavior critical to processes like film blowing, fiber spinning, and blow molding—data traditionally inaccessible via standard capillary methods.

The study evaluates three thermoplastics—LDPE, flexible PVC, and rigid PVC—using an instrumented extruder with interchangeable dies. Results are benchmarked against viscosity curves obtained on an Anton Paar MCR703 rheometer. Shear rate overlap is analyzed across five decades (0.01–10,000 s⁻¹), revealing extrusion’s superiority in high-shear process simulation and rheometer’s advantage in low-shear structural insight.

Key takeaways include:

1. Distinct shear range capabilities, with extrusion excelling above 100 s⁻¹
2. Complementary roles in predicting die swell, melt fracture, and final product defects
3. Strengths (extrusion: realistic processing conditions; rheometer: absolute viscosity) and weaknesses (extrusion: wall slip risks; rheometer: limited rate range)
4. Integrated workflows for robust formulation development and quality control