Ethylene methyl acrylate copolymer (EMA) assisted dispersion of few-layer graphene nanoplatelets (GNP) in poly(ethylene terephthalate) (PET)

Abstract

The inclusion of ethylene methyl acrylate copolymer (EMA) during the melt mixing of composites of poly(ethylene terephthalate) (PET) and graphene nanoplatelets (GNP) results in increased melt viscosity and shear stresses acting on the molten composite. This is due to ester groups of the acrylates in the co-monomer unit of EMA reacting via transesterification with PET creating cross-linked structures, as confirmed by solid state 13C magic-angle-spinning, nuclear magnetic resonance spectroscopy (13C MAS NMR), Fourier transform infrared (FTIR) spectroscopy and, isothermal time sweep oscillatory rheology measurements. The increase in shear stresses assists the exfoliation of the GNP in the PET matrix, resulting in lower electrical and percolation threshold values. The electrical percolation decreased from a volume fraction of 0.017 to 0.005 GNP and an AC conductivity of the PET-GNP composite on inclusion of EMA as high as 10 S/m attained. The rheological percolation threshold value halved from a volume fraction of ~0.0237 to ~0.0117. Both EMA and GNP had a nucleating effect on the PET, as the crystallization temperature (Tc) of PET increased by > 20 °C and the crystalline content (Xc) by >25%.