Upper Peltier Plate

According to federal standards, a sample of asphalt binder needs to be fully equilibrated to within 0.1 °C of the test temperature prior to performing rheological measurements. In the plot shown above, the temperature quickly and accurately jumps from 25 °C to 85 °C within minutes of starting the experiment. The data further shows that as soon as the temperature is within 0.1 °C, the viscosity of asphalt binder is fully equilibrated. No change is seen in the viscosity, even after 20 additional minutes indicating that there is minimal lag between the set-point and real sample temperature. Whether programming temperature steps, ramps or complex thermal profiles to closely simulate processing conditions, the UPP’s fast and precise response reduces the time between tests resulting in increased productivity without compromising the measurement accuracy.

Rheology data is often used to optimize processing conditions, such as identifying operating temperatures, molding cycle times, annealing and many others. Even small errors in temperature, especially non-uniform sample temperatures, lead to erroneous data, the implementation of incorrect processing conditions, and ultimately poor product performance.

The plot shows a temperature ramp on a plastisol using three temperature system configurations, a combined convection-radiation oven (ETC), a lower Peltier Plate only, and a lower Peltier Plate with the Upper Peltier Plate (UPP). A uniform temperature profile in the sample is achieved when the sample is heated from both the top and bottom, as in the ETC and UPP. Data from ETC and UPP configurations exactly match due to uniform heating of the sample from top and bottom. The hardening temperature, observed as a sharp increase in G’, occurs at approximately 60 °C. However, when heating the sample using only the lower Peltier Plate, the sample temperature lags the heating profile resulting in a temperature gradient in the sample. This results in what appears to be a delayed onset of curing at approximately 70 °C. The UPP’s direct temperature control enables users to obtain accurate and precise rheological measurements and unmatched data repeatability, even when compared to different temperature system configurations across their organization.

An adhesive’s success and suitability hinges on its ability to bond and resist debonding from a substrate. Measuring the viscoelastic properties, such as G’, G” and tan δ, allow users to quantify performance characteristics such as cohesive strength, tack, and operating temperature range. For example, the performance window of a pressure-sensitive adhesive (PSA) is highly sensitive to the Tg which defines the lowest use temperature of the PSA.

In this PSA example, an oscillation temperature ramp test was performed at 5 °C/min. The peak of the tan δ signal is used to determine the Tg of the material at 6.90 °C, indicating the lowest use temperature. The G’ and G” signals provide quantitative metrics of the cohesive strength and tack of the material from -30 °C to 200 °C. The tack and peel behavior can be further studied using frequency sweeps at the end-use temperatures. The UPP’s simple configuration delivers accurate temperature control, even at sub-ambient temperatures without needing liquid nitrogen or mechanical chillers.