Dynamic Mechanical Spectroscopy with Cylindrical Geometry: Application to the Comparison of Various Plasticizers of Thermoplastic Starch

Dynamic mechanical spectroscopy is a common analysis for polymers. Rectangular specimens are usually used for measurement in the solid state due to their easy designing. However, in reason of the non-symmetric shape of sample, rectangular specimens do not experience linear stress on their all body, leading to overestimation of shear modulus. Corrections are required to determine the right shear modulus. In this present work, straight shear modulus determination is carried out using specimens with a cylindrical shape. The reliability of the technique is described on a biosourced polymer materials made of thermoplastic starch, plasticized by glycerol, choline chloride/urea mixture (ChCl/U), 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl) and 1-ethyl-3-imidazolium acetate ([EMIM]Ac). The technique is shown to be particularly interesting to avoid any additional shaping of the specimens prior to measurements, that can be detrimental to their properties (evaporation, degradation). A comparison between cylinder and rectangular specimen has also been made to illustrate the interest of cylinder clamping on biosourced polymer material.