Process Optimization of Rubber Compounds using Capillary Rheometry Viscosity Measurements

A leading rubber products manufacturer was experiencing difficulty extruding un-vulcanized rubber. Formulation (recipe) changes produced unpredictable results.

An Instron CEAST SR20 (SmartRHEO 2000) capillary rheometer was to characterize the differences of three different rubber formulations at a constant rate of shear of extrusion at several discrete shear rates. The data presented demonstrate the instrument's ability to measure un-vulcanized rubber compound processing behavior at processing temperatures, pressures and shear rates.

The information obtained allowed us to make a determination of the quality incoming stock material as “good” or “bad” and reject any “bad” lots before spending any time in blending, further testing, pilot runs, etc. thus producing significant savings (it is widely accepted that the cost of one failed pilot run is about the same cost as the purchase of a rheometer). And finally, one could make adjustments to the processing conditions that would allow the “bad” sample to be successfully run to produce high quality final product. First pass suggestions may include adjustments to the extruder temperature, extruder speed (shear rate) or extruder torque (pressure) and one may be able to blend the “bad” material with the “good” material), rerun the capillary rheometer analysis and determine the material can be successfully blended to produce a high quality final product with only minor adjustments to the processing environment. As indicated above, this requires learning more about the processing conditions and correlating these conditions to the information obtained from the rheological data.

These results demonstrated the capability and versatility of the CEAST SmartRHEO capillary rheometer and its ability to report results over 4 decades of Shear and 3 decades of viscosity for these samples. Effectively resolve viscosity profile for all three uncured rubber materials. Efficiently predict material viscosity at various processing conditions. Define the ideal processing region (100 to 1000 s-1). And obtain this information in very short time when testing at the processing shear rates.