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The Effects of Particle Size on the Morphology and Properties of Polyimide/Nano-Al2O3 Composite Films

Polyimide/nano-sized Al2O3 composite films based on pyromellitic dianhydride(PMDA) and 4,4'-oxydianiline(ODA) were synthesized by incorporation with different particle sizes of nano-Al2O3 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 Al2O3 nano-particles had a great effect on the microstructures of composite films. The smaller size of the Al2O3 particles, the more regularity of composite films were obtained. Properties testing results indicated that by increasing the Al2O3 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 Al2O3 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 Al2O3 particles was used, which had a three times longer than PI composite film with largest Al2O3 addition.