Deep Trap Origins, Characteristics, and Related Mechanisms in Chemically Grafted Polypropylene with Enhanced Direct Current Volume Resistivity

Deep traps play an important role in the high-temperature dielectric properties enhancement of chemically grafting-modified polypropylene (PP), which is fairly promising in the field of insulation material application. This study quantitatively investigates the deep traps of methyl methacrylate (MMA)-grafted PP from three points of view: thermally stimulated depolarization current (TSDC), quantum chemistry computation, and direct current (DC) volume resistivity. The TSDC results indicate that grafted MMA groups can deepen the original trap level of PP and introduce a new deep trap level at about 2.0 eV. The trap origin and positive effect on macroscopic DC resistivity are analyzed and verified by quantum chemistry computation and space charge limited current (SCLC) theory, respectively. We interpret the deep trap of MMA-grafted PP from different perspectives and try to establish the correlations among trap origins, characteristics, and macroscopic manifestation. This work is expected to advance the understanding on trap characteristics of grafting-modified PP and promote the related mechanism research.