A combined experimental–numerical rheometric and mechanical characterization of EPM/EPDM rubber for medium voltage cable applications vulcanized with peroxides



The vulcanization of medium and high voltage (M-H V) cables is an important industrial application where manufacturers use principally EPM/EPDM, crosslinked polyethylene (XLPE) and now also thermoplastic rubbers. In the present article, an EPDM compound for medium voltage cables—normally distributed to producers in pellets and ready to be cured—is considered and several experimental tests (rheometer curves and mechanical characterizations) are conducted changing controlled curing temperature, peroxide type and peroxide concentration. In particular, tests are replicated in a temperature range between 160 and 200°C, with data provided every 20°C, using two different peroxides, a mixture of three commercial peroxides at five different concentrations. A huge amount of experimental data (cure curves) is obtained (one for each temperature, peroxide used and concentration) and results are critically compared one each other, to have a quantitative insight into the most effective temperature and peroxide to be used during this kind of vulcanization, with the aim of maximizing vulcanization velocity, final torque reached and mechanical properties of cured rubber. The comprehensive experimental study proposed is finally assessed from a numerical point of view, utilizing a complex kinetic scheme constituted by reactions occurring in series and parallel, which allows estimating numerically the vulcanization degree by means of a single second order nonlinear differential equation, with unknown parameters determined through non-linear least squares fitting, with target data represented by experimental rheoemeter curves. The experimental fitting is almost perfect for all the cases analyzed and is aimed at predicting (without an expensive experimentation) the most suitable production parameters (e.g., curing time and temperature) to guarantee improved mechanical properties and a good aging resistance of the items. In addition, the numerical approach could allow finding the most suitable recipe, also in presence of mixtures of peroxides, able to provide items with a uniform vulcanization level. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40075.