Effects of Wax Components and the Cooling Rate on Crystal Morphology and Mechanical Properties of Wax-Oil Mixtures

Crystal morphologies of different binary and ternary "model mixtures" were investigated using different cooling conditions (with cooling rates from 0.1 to more than 300 degrees C min-1). Needle-like crystals tend to form in binary mixtures under fast cooling, while uncommon spherulitic crystals were observed in ternary mixtures under slow cooling. These differences in crystal morphology lead to distinct mechanical behavior of the "model mixtures". As shown by cone penetration tests, mixtures with spherulitic crystals exhibit a lower mechanical strength than those with densely arranged needle-like crystals. In addition, nanoindentation tests demonstrated that Young's modulus and plasticity limit of mixtures are higher upon faster cooling. Lipstick-shaped cast samples were studied, in which cooling rates are much higher at the surface than at the center. A gradual change in crystal morphology was observed from surface to center, correlating to the hard surface and the soft center as revealed by nanoindentation tests. This work illustrates the relationship between process thermal control, microstructure morphology, and mechanical properties for wax-oil mixtures, paving the way to the monitoring of sensorial properties by control of mixture composition and process control.