Thermal and mechanical properties of industrial benchmark lipstick prototypes

Abstract

We studied the thermomechanical properties of eight original, industrial-grade, and commercially available benchmark lipstick prototypes, some of which serve as international market leaders. The thermal properties, i.e., the melting peak distribution, the degree of crystallization, and the softening point, were investigated using differential scanning calorimetry. Additionally, we investigated the linear and nonlinear viscoelastic properties as well as the flow melting behavior under oscillatory shear stresses. We recorded both polymorphic melting profiles with multiple, narrow as well as single, broad melting peaks. Stable networks, less endothermic events, and a more desired extent of crystallinity validate the market popularity of some of the benchmark prototypes. We observed a prototype-dependent resistance to the deforming strain and temperature, decent short-term mechanical stability, intercycle strain thinning of both dynamic moduli at high strain amplitudes, and predominant elasticity at quasi-steady state. The temperature sweeps mainly indicated gel-like behavior. This study has both fundamental and application-oriented aspects. Namely, in addition to establishing thermomechanical reference values, we discuss them from a textural perspective and relate them to different consumer groups. Besides, we reveal the full mechanical continuum under low to high strains, give the strain tolerance limits, and present innovative concepts like the intrinsic sample elasticity. The results of this study can guide the development of next-generation lipsticks, including natural component-based samples with active ingredients.