Overcoming Rheological Challenges Associated with Characterizing Soft Polymeric Samples

Polymer-based products are widely used in a plethora of industries ranging from packaging, automotive, medicine, and architecture to home care. Mechanical and thermal analysis methods are essential to guarantee good quality and performance of the final products. Modern rheometers offer the user a wide range of both rotational and oscillation-based tests. Oscillatory measurements allow characterizing the viscoelastic properties of the polymer within a broad range of frequencies and temperatures. Time-temperature superposition (TTS) is of great interest to characterize samples over a wide range of temperatures and frequencies. 

One often runs into rheometric limitations while performing such tests on soft polymeric materials. In this webinar, a pressure-sensitive adhesive (PSA) will be used as a model soft polymeric material. For instance, due to the huge range of temperature and frequency which are probed one has to change the configuration which includes changing the plate diameter and using a new sample. When performing torsional tests, one challenge is that both, the sample between the plates as well as the components of the rheometer (such as measuring system and motor) are exposed to torsional stresses. If the sample is rather liquid and much less stiff than the measuring system, all torsional energy is absorbed by the sample, i.e. the deflection angle of the motor is the same as the deflection angle of the sample. However, if the sample is very stiff, e.g. soft polymers exposed to very low temperatures, the rheometer components are also torsionally twisted resulting in a deflection angle of the sample being less than the deflection angle at the motor. Another challenge is oscillating at high frequencies. Due to the inertia of the moving rheometer components and the sample, the torque necessary to accelerate the measuring system becomes eventually much larger than the sample torque. This can lead to spurious results and one has to account for such effects. 

In this presentation, we will show the strategy to perform TTS measurements on a soft polymeric system (pressure-sensitive adhesive) over a huge temperature (200°C) and moduli (6-7 decades) range without having to change the configuration and/or the sample.