Thermal Fractionation Technique to Evaluate the Effect of Microstructure Defects on Dielectric Properties of Polypropylene

The successive self-nucleation and annealing thermal fractionation (SSA) technique offers a practical way to evaluate the chain crystallization behavior according to the length of polymer crystalline sequence. In this paper, three polypropylene resin (PP) samples with different heat resistance grades were characterized combined SSA and electrical measurement, and the relationship between molecular structure and high temperature dielectric properties of PP was established. The results indicate that the lamellar sequence length distribution coefficient can reflect the molecular interchain defects, which determines the insulation property of the PP resin. The PP-2 sample with high crystallinity and narrow lamellar sequence length distribution shows the most excellent high temperature dielectric property, which can be applied in the field of oil-immersed capacitor film. There is a good correspondence between SSA analysis results and electrical test values, which implies the SSA technique has the advantage in real-time monitoring the molecular structure to effectively evaluate the macroscopic electrical insulation property of PP resin.