Implementing new elastomer compounds into a production process is complicated, but using torque rheometry can ease that transition. We provide practical examples to demonstrate the various process parameters that can be evaluated and analyzed by a torque rheometer prior to the initial transfer to production.
In the lab, a new material has been developed specifically to improve or adjust its properties to make better products for your company. However, hundreds of process parameters will change when the process is scaled up; larger volumes, different environments, and heavily used production equipment are all inherently different than the lab environment.
Is there a way to anticipate process changes prior to production, so that when similar results are seen in production, the process engineer knows exactly the parameters to adjust to achieve the correct result?
Torque rheometers, equipped with laboratory-scaled internal mixers, have been used in the rubber industry for decades. These instruments process small rubber samples in conditions similar to those encountered in production. Using this type of torque rheometer, many process parameters can be evaluated at laboratory scale, resulting in clearer understanding of the material properties long before the new material hits production. (See video.)
Curing
Using a torque rheometer allows testing for minimum viscosity, the onset of scorching and the rate of cure for various additives. The small volume size allows multiple polymer/additive combinations to be graded and determine which compound ingredients affect material properties.
Mastication
Rubber polymers require the mastication process to reduce their viscosity and even out variations between lots. Using a torque rheometer, the initial flow properties of the sample can be evaluated, by using the torque peak caused by the high resistance of shear while cold.
Viscosity
Strongly dependent on the shear rate, different non-Newtonian liquid elastomers of equal molecular weight may exhibit the same viscosity at high shear rates. However, by varying the shear rate to extremely slow rates, by reducing rotor speeds perhaps, differences between polymers is often detected.
Flow-Curing Behavior
Vulcanization occurs at a higher temperature in elastomers when curing agents such as sulphur are added. The vulcanization process is best monitored at its onset; important process parameters include the ways in which mixing, extrusion or injection molding affect the onset of vulcanization, which in turn, affects viscosity.
When a torque rheometer has automated extrusion-capillary, die swell behavior, and qualitative testing of extreme shapes — which all provide valuable information when solving problems in the production processing of un-vulcanized rubber — there is insight into such parameters as viscosity, elasticity, and extrudability.
Using rheology to identify which process parameters affect which properties while the material is still in the lab setting will enable process engineers to quickly evaluate and adjust production parameters. Read this application note to see how a Torque Rheometer can speed the process of scaling up to production scale.
Additional Resources
- Video: Thermo Scientific™ HAAKE™ PolyLab™ Torque Rheometer
- Brochure: Thermo Scientific™ HAAKE™ PolyLab Torque Rheometer
- Application note: Torque Rheometer can speed the process of scaling up to production scale.
Editor’s Note: This article was previously published in February 2019 but has been updated and refreshed.
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