Compatibility Analysis of Isotactic Polypropylene/Elastomer Blends for Power Cable Insulation Based on Numerical Simulations

Abstract

Using elastomers to toughen the isotactic polypropylene (iPP) for power cable insulation is an economically efficient and widely recognized method. However, the selection of elastomers mostly relies on experience, and the compatibility between iPP and elastomers lacks quantitative characterization. In this paper, molecular dynamics (MD) and mesoscopic dynamics (MesoDyn) simulations were used to analyze the compatibility between iPP and elastomers. The molecular weights of iPP and two types of elastomers, propylene-based elastomer (PBE) and ethylene-octene copolymer (EOC) were measured by Gel permeation chromatography (GPC) to obtain simulation parameters. Molecular and mesoscopic models of iPP/elastomer blends were established, and the compatibility between iPP and elastomers was analyzed according to the monomer, molecular chain, and aggregated structures. The results showed that the compatibility of iPP and PBE was higher than that of iPP and EOC. The mixing energy and interaction parameter of iPP/PBE were close to 0. The solubility parameters of iPP and PBE were approximate, and the binding energy of iPP/PBE was higher than that of iPP/EOC. The dispersion of PBE Gauss chains in the iPP matrix is better than that of EOC. With the increase of the elastomer content, the order parameter of the iPP/elastomer blend increased to above 0.1, from compatible system to incompatible system. The compatibility threshold of iPP/PBE was 20 wt% of the elastomer content, while that of iPP/EOC was 10 wt% of the elastomer content. The simulation results of the compatibility were closely related to the mechanical and electrical properties of the blends. It is suggested that the simulation method can provide a reference for the determination of the types and contents of elastomers in the investigation of iPP-based cable insulation materials.