An extremely uniform dispersion of MWCNTs in olefin block copolymers significantly enhances electrical and mechanical performances

Abstract

Ethylene-α-octene copolymers with different chain architectures (ethylene-α-octene random copolymer (ORC) and ethylene-α-octene block copolymer (OBC)) were adopted to prepare elastomeric composites with multi-walled carbon nanotubes (MWCNTs) through melt mixing. Extremely uniform dispersions of MWCNTs in OBC and serious aggregations of MWCNTs in ORC were observed. The percolation threshold of OBC composites was 2.5 vol%, much lower than that of ORC composites. Rheological measurements and thermodynamic analysis revealed that the uniform dispersion of MWCNTs in OBC is due to the selective localization of the nanotubes in the molten state, and the stronger volume exclusion effect of OBC crystals in nanoscopic dimensions towards nanotubes also accounts for the developed MWCNT network after crystallization. Although OBC itself showed lower stress at a certain stretching and tensile modulus than that of ORC, the percentages of reinforcement in stress at a certain stretching and tensile modulus of OBC composites were almost twice as much as that of ORC composites at the same content of MWCNTs. Elongations of OBC composites were all higher than 1600% (even when the MWCNT content was as high as 7.84 vol%) and were always at least 200% larger than that of ORC composites at the same content of MWCNTs. The results provide significant guidance for the preparation of conductive elastomeric materials with both excellent electrical performance and mechanical properties by utilizing thermoplastic polyolefin copolymers with blocky chain architectures.