Cold crystallization event on DSC heating curves of bitumen

Abstract

Differential scanning calorimetry (DSC) is the main technique of studying the thermal behavior and forming the structure of bitumen. One of the thermal effects on the DSC heating curves in the study of bitumen is a low-temperature exotherm. The origin and features of this phenomenon formation have not yet been investigated despite the relevance of the issue. Inaccuracy of this exotherm identification leads to an incorrect estimation of the quantitative parameters of the low-temperature glass transition and the amount of the crystalline fraction of bitumen. Using the temperature-modulated DSC (TMDSC) method, it is shown that the low-temperature exotherm is due to the cold crystallization of wax molecules. The dependences of the cold crystallization exotherm enthalpy on various experimental conditions, such as the annealing time and temperature, and the cooling rate are investigated. It is established that these conditions affect the value of the cold crystallization exotherm enthalpy through a change in the amount of the substance involved in the process. In order to avoid incorrect identification and interpretation, a comparative analysis of the conditions for the formation of cold crystallization event with another exothermic effect observed on the DSC heating curves of bitumen—the exothermic recrystallization of secondary wax crystals—was performed. The results obtained can be used as reference information for the study of bitumen by TMDSC and conventional DSC method.