Rheological and phase behaviour of paraffin wax/bitumen blends with thermal storage characteristics

This paper analyses the thermomechanical properties, heat storage characteristics and compatibility of bitumen blends with a paraffin wax, having a melting point around 60 °C, as phase change material. To that end, temperature sweeps in the linear viscoelastic range, technological properties, Modulated Differential Scanning Calorimetry (MDSC), and cross-polarised optical microscopy observations were carried out on blends and pure compounds. The obtained results reveal a partial compatibility between the compounds and the development of a multiphasic microstructure, where the paraffin-rich or bitumen-rich domains form the continuous phase depending on the concentration, with the phase inversion around 20 wt% wax. Below this threshold concentration, the disperse paraffin-rich phase acts as filler that reinforces the continuous bitumen matrix until it reaches the melting transition. Above the critical concentration for the phase inversion, the continuous paraffin-rich phase controls the rheological response. However, both phases retain their own identity and show their individual transitions and relaxations. Despite the partial compatibility, a high degree of crystallinity is found, especially for high paraffin contents, which would result in a significant capacity to store thermal energy, for applications such as solar thermal collection or thermoregulation materials for buildings, etc.