Composites based on neat and modified asphaltenes and paraffin: Structure, rheology and heat conductivity

Abstract The work is devoted to evaluation of the thermal conductivity of composites based on asphaltenes and paraffin as a phase change material. Asphaltenes with different structural characteristics, obtained by chemical modification and fractionation were used to improve the heat conductivity of paraffin. Modification of asphaltenes with sulfuric acid and oleum made it possible to obtain samples with increased content of condensed structure fragments and minimum content of aliphatic ones. The form of modified asphaltenes neutralized with diethanolamine was also investigated. Asphaltene molecules with increased aliphatic content were isolated by fractionation with toluene / acetone mixtures. Structural, thermophysical and rheological properties of composites based on paraffin and these types of asphaltenes are analyzed. It is shown that the introduction of asphaltenes into the paraffin matrix does not violate its ability to crystallize, but leads to a decrease in the degree of crystallinity and an increase in the crystallization temperature. The increased content of the condensed structures in modified asphaltenes leads to strong agglomeration, and as a result, to a decrease in the thermal conductivity of the composite material at room temperature. The introduction of asphaltenes with high aliphatic fragments content ensures their more uniform distribution in the paraffin matrix, which contributes to an increase in the thermal conductivity of the system.