Rheology Testing Lab
Industrial Applications
A. Rheology for Curing and Reactive Systems
Rheology testing of reactive materials that thicken with time, is well described by ASTM D4473-08. This method outlines Dynamic Mechanical Properties: Cure Behavior. The test methods can be used to measure the rate of cure and cure time as it relates to gelation. This method has applications to various industries including biomedical and industrial for glues and adhesives. How much working time is there before the material is too thick to manipulate? We can measure that.
Cure Measurement Using Rheometers
Rheometers are well designed for cure measurements using isothermal time sweeps, for example, at constant frequency and strain. One can measure the progressive increase in viscosity as the compound hardens and cures. However, available commercial rheometers are problematic in cure testing for a number of serious reasons. Most important is potential damage to sensitive transducers that follow the cure to thickening, and the setting of the cements on fixed rheometer tooling. Perhaps the most important is the hazardous nature of polymer systems used in adhesive applications. Rheometers are seldom designed for easy placement in exhaust hoods.
An alternative rheometer was designed to eliminate many of these problems, at a very reasonable price point. The rheometer was designed to be portable and affordable – the TSR Rheometer.
TSR Rheometer Background
The TSR rheometer (Thermal Scanning Rheometer) was designed and marketed by Polymer Labs many years ago. It measured cure of reactive polymers very simply using an oscillating solenoid valve attached to a spring-loaded tooling. This instrument is described in “The Applications of the Strathclyde Rheometer to a Variety of Curing Systems”. The article is published in Rheology of Food, Pharmaceutical and Biological Materials with General Rheology, Elsevier Applied Science,Ed, R.E. Baker., 1989. The instrument concept eliminated the problems with using a sensitive research grade rheometer for cure testing while obtaining comparable results. The sample holder and the test tooling are disposable.
Current Capabilities
An updated version of this instrument is available at Fluid Dynamics Testing. The rheometer can study the curing behavior of glues, bone cements, caulks, paints, coatings and dental substrates.
The graph above shows an example of data that can be obtained from the cure device, the loss modulus, G”, storage modulus, G’, and complex viscosity, n* (Eta*).
The instrument is portable and does not need dry, compressed air.
B. Rheology as a problem solving tool
There are many examples of rheology being an excellent problem solving tool. A good example is defining the consumer market place for personal and/or household care products.
When designing new products or product improvements, i.e., next generation products, what mechanical properties are pertinent? Do these properties change within premium brands, low cost generics, or specialty products? Do mechanical properties across various commercial brands vary by market share? In consumer research, do consumers prefer thick, thin, foamy, viscoelastic gel-type products?
Many of these questions can be answered by a rheology test suite for a comprehensive market analysis, domestic and/or internationally. In one example, the shear thinning of various products can be determined over a solid working range of shear rates at the temperature of interest. The graph shows the steady state viscosity at four shear rates, room temperature, for six commercial moisturizers.
