Thermoresponsive Behavior of Binary Waxes

In this study, we investigated the thermoresponsive behavior of two different binary wax compositions of commercially available natural candles. The chemical nature of carbon bonds in the fatty acid chains of the natural wax component effectuate a different hygroscopic behavior, as confirmed by NMR analysis. The phase transitions of polymorphic stearin-rapeseed and stearin-coconut wax composites were tracked by DSC-TGA and VT-XRD. The reduction in the eutectic temperatures of wax composites during the second heating cycles of DSC measurements was correlated with the length of fatty acid chains in rapeseed and coconut waxes, as well as their co-crystallization kinetics with stearin. Mechanical and hygroscopic behavior of the binary waxes were examined at elevated temperatures between 23 °C and 45 °C using QCM-D. Voigt viscoelastic model was employed to reveal the soft and rigid textures of wax composites. The hydrophilic behavior of the rapeseed wax composite changed to hydrophobic when the co-crystallized and individual stearin melted above 35 °C. Activation energies required for melting wax crystals were calculated to be 51±3 kJ mol−1 for pure rapeseed wax, 373 kJ mol−1 for co-crystallized rapeseed and stearin waxes, and 244 kJ mol−1 for co-crystallized coconut and stearin waxes, using Arrhenius method with the QCM-D data.