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Extensional rheology is a technique complementary to shear rheology, enhancing comprehension of a material’s deformation and flow behavior under different stress conditions. Although shear tests are relatively straightforward with rotational rheometers, instruments for extensional rheology have undergone numerous improvements over the last six decades to address challenges of testing molten polymers at high temperatures and difficulties in predicting sample geometry under large uniaxial extension. A powerful method for accounting for specific geometry modifications under high normal stresses is to perform extensional tests in which the crosshead speed is controlled by a feedback-loop program throughout the entire duration of the test. This method is implemented on the Versatile Accurate Deformation Extensional Rheometer (VADER 1000). However, this device is limited to relatively soft samples. Moreover, there is, today, no clear method capable of bridging the viscoelastic elongation properties of a polymer in its molten state to its properties in the solid state. We report here a methodology using an Instron tensile machine for extensional rheological tests, highlighting its capability to operate over a broad temperature range and to characterize samples that may not readily adhere to metal surfaces. We evaluate the validity of the method by analyzing elongation properties of a polydisperse polystyrene sample in its molten state. Results obtained using a constant Hencky strain rate profile on an Instron 68TM-10 instrument were found to be in very good agreement with the measurements from a VADER 1000 device and from an Extensional Viscosity Fixture on an Advanced Rheometric Expansion System.
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Boborodea, A., Sallem, N., Janssens, F., & Van Ruymbeke, E. (2026). Elongation properties of a polymer melt: How to measure its rheological response with a tensile machine? Journal of Rheology, 70(2), 269-279. https://doi.org/10.1122/8.0001133 (Original work published 2026)