The Effects of Particle Size on the Morphology and Properties of Polyimide/Nano-Al ₂ O ₃ Composite Films

Polyimide/nano-sized Al ₂ O ₃ composite films based on pyromellitic dianhydride(PMDA) and 4,4'-oxydianiline(ODA) were synthesized by incorporation with different particle sizes of nano-Al ₂ O ₃ via in situ polymerization. The morphology and structure of composite films were studied by scanning electronic microscopy (SEM). The properties including the tensile strength, corona resistance, electric breakdown strength and dielectric properties were investigated. Results indicated that the size of Al ₂ O ₃ nano-particles had a great effect on the microstructures of composite films. The smaller size of the Al ₂ O ₃ particles, the more regularity of composite films were obtained. Properties testing results indicated that by increasing the Al ₂ O ₃ particles' dimension would decrease the mechanical properties and electric breakdown strength of composite films, while the dielectric constant remain nearly stable. Results also showed that after Al ₂ O ₃ addition, the corona resistance of composite films was improved, compared with that of pure PI films. The longest corona resistance time was obtained when the smallest Al ₂ O ₃ particles was used, which had a three times longer than PI composite film with largest Al ₂ O ₃ addition.