Higher-Order Structure in Amorphous Poly(ethylene terephthalate)/Graphene Nanocomposites and Its Correlation with Bulk Mechanical Properties

Abstract

Graphene of two different aspect ratios, Af, was melt mixed with poly(ethylene terephthalate) (PET) to form amorphous PET/graphene composites with less than 5% crystallinity. The higher-order structure and mechanical properties of poly(ethylene terephthalate) (PET) in these composites were investigated using techniques such as differential scanning calorimetry and dynamic mechanical analysis, whereas transmission electron microscopy, melt rheology, and electrical conductivity were used to study the graphene dispersion. A decrease in heat capacity changes, ΔCp, of PET in nanocomposites at the glass transition temperature, Tg, without Tg change suggests that a rigid amorphous fraction (RAF) of PET was formed at the PET/graphene interface. The stiffening effect of graphene below 1 wt % loading is quite small in the glassy state region and independent of the Af of graphene. Above 2 wt %, graphene forms a mechanical percolation network with the RAF of PET and the PET chains are geometrically restricted by the incorporation of graphene with a high Af, resulting in an unexpectedly higher modulus of nanocomposites both below and above Tg.