Production and characterization of novel EPDM/NBR panels with paraffin for potential thermal energy storage applications

Innovative panels suitable for the thermal management of closed systems with potential applications for buildings have been produced combining an Ethylene-Propylene Diene Monomer (EPDM) rubber with a paraffin wax having a melting temperature of 28 °C. The compounded material was confined in a Nitrile Butadiene Rubber (NBR) envelope that impeded any paraffin leakage. According to differential scanning calorimetry, the effective thermal energy efficiency of the PCM (PCMeff) in the panel, was 37 wt% with a melting enthalpy of about 100 J/g. The homogeneous distribution of paraffin within the elastomeric matrix was verified both through scanning electron microscopy and through temperature monitoring of the panel’s surface during heating/cooling cycles, performed by an infrared camera. It was also observed that the thermal conductivity of the panels was the same above or below the melting point of paraffin with values of about 0.15 W/m·K. Shore A hardness tests revealed the dependence on the temperature due to the presence of paraffin that acted as softener above its melting point and as hardener below. The evaluation of the thermal energy storage performance of the panels was verified by monitoring the internal temperature of testing boxes (310x310x310 mm3) insulated with these elastomeric panels during heating/cooling cycles performed in a temperature interval from 16 to 31 °C (typical summer conditions in Trento, Italy). The presence of paraffin within the elastomeric panels allowed to keep the internal temperature of the box always lower than 27 °C, with a delay of the peak temperature of about 1 h with respect to a reference non-insulated box. The results of testing boxes have been confirmed after 15 months, showing the reproducibility and the stability of the assembled lab configuration.