Polyurethane/graphene (PU/RGO) nanocomposites were prepared by in situ polymerization of the residual hydroxyl or carboxyl groups on graphene with the castor oil-based polyurethane prepolymer

and their molecular structures were characterized by FTIR and Raman spectroscopy.In addition

the thermal stability and morphological structure and resistivity-temperature behavior of PU/RGO nanocomposites were investigated by thermogravimetric analyzer (TGA)

X-ray diffraction (XRD)

scanning electron microscope (SEM) and ZC36 high resistance meter

respectively.The results indicated that the addition of the graphene led to the increase in the cross-linked network owing to the reaction of more-NCO groups of PU with graphenes

and the enhancement in physical crosslink amongst the polyurethane-based composites owing to the effect of the relative free graphene residual.As a result

the PU/RGO composites showed a slight increase in room-temperature resistivity due to the combined effect of crosslink network and physical crosslink reaction on the conductive network.When the temperature value reached a critical temperature

the rapid expansion of the volume of PU-based polymer destroyed the significant reductive network of graphene

resulting in the remarkable enhancement in the resistivity-temperature behavior of PU/RGO composites.Especially

at the loading of 3 wt% graphene hybrid filler in PU matrix

PTCR behavior of the composites was observed with resistivity increase of nearly 3 orders of magnitude.Therefore

it is expected that the PU-based composites with a few contents of graphene might be the promising PTCR materials.