Mechanical and stress relaxation behavior of Santoprene® thermoplastic elastomer/boehmite alumina nanocomposites produced by water-mediated and direct melt compounding

Thermoplastic dynamic vulcanizate (TPV) was filled with synthetic boehmite alumina (BA) via water-mediated (WM) and direct melt compounding (DM) techniques. According to the WM an aqueous BA dispersion was injected into the molten TPV in a twin-screw extruder to prepare the related nanocomposite with 5 wt.% BA content. In DM the BA powder was mixed to the TPV granules in the hopper of the extruder. The dispersion of the BA was studied by atomic force microscopy (AFM), and discussed. The mechanical and thermo-mechanical properties of the composites were determined in uniaxial static tensile, dynamic-mechanical thermal analysis (DMTA), and short-time stress relaxation tests (performed at various temperatures). It was found that the WM technique yielded a finer BA dispersion in TPV than the DM one. Incorporation of BA increased the stiffness, elongation at break and relaxation modulus compared to the neat TPV. Effect of the BA incorporation route was most pronounced for the stress relaxation results. Master curves, displaying the relaxation modulus vs. time, were constructed by applying the time–temperature-superposition principle. It was established that the Williams–Landel–Ferry equation (WLF), and the generalized Maxwell model are fairly applicable to the stress relaxation results.