Roles of polycyclic compounds in increasing breakdown strength of LDPE film

Polycyclic compounds of acene series without radicals were added to the. material of LDPE (low density polyethylene) film to investigate the roles of aromatic compounds in an increase in the breakdown strength (BDS) of the film. The additives used were naphthalene, anthracene, tetracene and pentacene (group A). De and impulse BDSs of the film with anthracene were the highest among the films with the group A additives. It was estimated from our experiments that dc breakdown of the film in this study is mainly due to the electron avalanche mechanism. Furthermore, the dependence of BDS upon the type of radical connected to anthracene (An) was measured using three kinds of additive (group B), which are 9,10-dibromoanthracene (Br-An), 9-nitroanthracene (NO-An) and I-aminoanthracene (NH-An). DcBDS of the films with radicals are arranged in the following order: (PE/NO-An) >=(PE/Br-An)>(PE/An)>(PE/NH-An). DcBDS of (PE/NO-An) was approximately 1.65 times higher than that of the film without an additive. The dependence of dcBDS upon the type of radical connected to An was,discussed using the experimental results with UV absorbance, DSC and TSC. The dependence of dcBDS on the kind of group B additive corresponds to the dependence of trap depth for electron carriers on the type of connected radical: the electron-accepting or electron-donating, or halogen type. The excitation of the additive at the collision with electron carriers is considered to increase dcBDS for all the films with the additives of group B and An. The modification of the morphology is not observed significantly in the films studied.