Extrusion foaming of multiphasic polyethylene/ethylene-vinyl acetate copolymer/carbon nanotube mixtures: Tailoring foam properties by selective localization of nanoparticles

Semi-conductive foams based on low-density polyethylene/ethylene-vinyl acetate copolymer (LDPE/EVA) blends in the presence of carbon nanotubes (CNTs) were prepared using a twin-screw extrusion process. The effects of CNTs content and localization state in the binary mixture on the physical and structural properties of LDPE/EVA/CNT foams were investigated. The results confirmed that the void fraction, cell density, bubble size and cell size distribution of foams are optimal against CNT loading. The lightest LDPE/EVA/CNT foam was obtained by the CNT localization in the LDPE matrix. This foam containing 2.5 phr of CNT had smaller cells and more uniform cell size comparing to the pure blend foam. The cell density of this foam was 1.598 × 106 cells/cm3, which is much larger than that for the blend foam, 8.64 × 105 cells/cm3. However, the CNT localization state in the dispersed EVA domains resulted in lower void fractions and cell densities comparing with the LDPE/EVA blend foam. The findings clarify the profound impact of the nanofiller localization state on the foam properties of the binary polymeric systems. Light semiconductive LDPE/EVA foams with small cells, uniform cell size and high cell densities were achieved by localizing and dispersing the CNT nanoparticles in the LDPE matrix phase.