Wall Slip-Free Viscosity Determination of Filled Rubber Compounds Using Steady-State Shear Measurements.

Area of Science:

• Polymer Science
• Materials Science
• Rheology

Background:

• High-pressure capillary rheometers (HPCR) are used for rheological properties of plastics and rubber.
• Rubber compounds exhibit flow anomalies and non-isothermal effects, impacting measurement accuracy.
• Existing methods assume isothermal flow and wall adhesion, which are often violated in practice.

Purpose of the Study:

• To investigate the applicability of the Cox-Merz rule for rubber compounds using HPCR.
• To develop an alternative method for accurate rheological measurements of rubber compounds.
• To compare the new method with existing techniques.

Main Methods:

• Empirical rheological transfer function of the Cox-Merz rule was investigated.
• High-pressure capillary rheometer (HPCR) and closed cavity rheometer (CCR) were used.
• A new methodology using ramp tests in a CCR was developed for wall slip-free, isothermal data collection.

Main Results:

• The Cox-Merz relation could not be verified for unfilled EPDM or filled rubber compounds.
• The CCR-based ramp test methodology yielded steady-state shear viscosity data.
• The generated data showed high agreement with corrected HPCR viscosity data.

Conclusions:

• The Cox-Merz rule is not applicable for characterizing the rheology of rubber compounds.
• The developed CCR methodology provides accurate, isothermal, wall slip-free viscosity data.
• The CCR method is more efficient than traditional HPCR methods for rubber compounds.