Thermal behaviour of low and high molecular weight paraffin waxes used for designing phase change materials

Two waxes, a soft petroleum wax and a hard Fischer–Tropsch paraffin wax, have been investigated to find the reasons for multiple endothermic peaks observed during heating in a DSC. DSC curves, molar mass distribution curves, and variable-temperature XRD results were compared, and it was confirmed that the first endothermic peak for the soft petroleum wax was due to a solid–solid transition, while the second endothermic peak was due to melting. However, for the hard Fischer–Tropsch paraffin wax there was no evidence of a solid–solid transition, and it was concluded that the multiple endothermic peaks in this case were due to melting of different molar mass fractions.