Electret Composite Materials Based on Polyethylene and Petroleum Asphaltenes

Petroleum asphaltenes as well as their derivatives obtained by sulfonation are studied as model fillers in this work. There corresponding particle size (distribution), specific surface area, and elemental composition are described. It is found that the introduction of petroleum components into a polyethylene (PE) matrix improves its electret characteristics (for example, the surface charge density value for PE after 30 days of storage is reduced to $0.07~\mu $ C/m2, whereas PE compositions with asphaltenes reached $0.190~\mu $ C/m2 and samples with modified asphaltenes $0.382~\mu $ C/m2). An increase in the number of sulfonic groups during the modification of asphaltenes leads to the creation of additional charge traps with even higher energies. This, in turn, leads to a significant (almost 2 times) improvement of the PE composites’ electret characteristics. The best electret properties are obtained for a polyethylene composition with 7.5 wt.% sulfonated asphaltenes (SA). The introduction of asphaltenes and SAs increases the thermal stability of the PE electrets by increasing the thermal resistance of the polymer itself. It can be explained by the fact that asphaltenes are more resistant to thermal degradation, and SAs increase the thermal stability of polyethylene even more effectively. The obtained composites can be considered as model systems, as they provide a way to further enhance the thermal stability for polymers electret with traditional fillers by means of particles surface chemical modification.