An insight into simultaneous phase transition phenomena and melt-rheology of low-density polyethylene/ethylene–vinyl acetate copolymer/expanded graphite nanocomposites through continuous extrusion foaming process

Abstract

In the present article, the influences of expanded graphites (EGs) with small, medium, and large aspect ratios (SEG, MEG, and LEG, respectively) on the foamability of low-density polyethylene (LDPE)/ethylene–vinyl acetate copolymer (EVA) blend obtained from continuous extrusion foaming process were studied. The addition of EGs to the PE/EVA blend resulted in foams with smaller cells and higher cell densities. Among the different nanofillers used, EG with larger aspect ratio caused the formation of PE/EVA foams with higher void fraction, smaller cell size and larger cell density. EG nanoplatelets assisted bubble nucleation and acted as an impermeable barrier against the gas removal from the melt, where LEG behaved more successfully due to having a larger surface area with the melt. During the bubble nucleation and growth stages, PE/EVA liquid–liquid and solid–liquid phase separations took place concurrently. The presence of EG nanofillers influenced the PE/EVA phase separation and increased the mutual solubility of the polymeric constituents in each other. Besides, EG nanolayers enhanced the viscoelastic properties of PE/EVA melt, and thus prevented cell wall rupture and gas release from the melt.