Effect of the filler on the nanomechanical properties of polypropylene in contact with paraffinic phase change material

Abstract

As the changes on the mechanical properties with depth of indentation provide valuable information that may be suitable for design purposes, nanoindentation is an adequate technique for investigating the nanomechanical changes in the surface and in the inner polymers. This research focuses on the study of the nanomechanical properties of two grades of polypropylene (PP) after the long term exposure to an organic fluid, such as paraffin wax used as a phase change materials (PCM). PCM are used for thermal energy storage (TES) in buildings applications for passive systems or heating and cooling usages. In any of these uses PCM must be encapsulated and PP is a possibility within the container materials used. Four different samples of the polypropylene were evaluated: PP, filled polypropylene with 60% Mg(OH)2 (PP-60Mg), PP-60Mg with PCM (RT-25), and PP-60Mg with PCM (RT-42). It was studied the thermal stability by Thermogravimetrical analysis of these samples, and also it was evaluated the Hardness (H), Elastic modulus (E) and Loss modulus (Eloss) for the unfilled PP and PP-60Mg in contact with two different PCM at different temperatures (30 °C, 45 °C and 60 °C for RT-25 and 45 °C for RT-42) for 32 days. Results show that the mechanical properties H, E, and Eloss are higher for PP-60Mg than for PP. Nevertheless, these properties decrease significantly when the PP and the PP-60Mg are in contact with PCM, because it acts as a plasticizer, softening the polymer. Besides, the higher PCM's melting point, the lowest mechanical properties were observed.