A molecular dynamics-based investigation on tribological properties of functionalized graphene reinforced thermoplastic polyurethane nanocomposites

Abstract

Tribo-mechanical properties of pure thermoplastic polyurethane and functionalized monolayer graphene-reinforced thermoplastic polyurethane polymer nanocomposites are investigated by molecular dynamics simulations. Initially, the mechanical properties of the thermoplastic polyurethane and functionalized monolayer graphene-reinforced thermoplastic polyurethane nanocomposites are measured by applying constant stain method. Subsequently, interfacial layer models are developed to apply confined shear on the iron layers to find out the coefficient of friction and the abrasion rate of pure thermoplastic polyurethane and functionalized monolayer graphene-reinforced thermoplastic polyurethane nanocomposites. The results imply that by the incorporation of 0.5 wt.% functionalized monolayer, graphene shows the increase of 20% in Young’s modulus, 15% in shear modulus and 6.66% in bulk modulus of pure thermoplastic polyurethane, respectively, which are in good agreement with the previous experimental studies. Maximum enhancement of mechanical properties can be obtained up to 3 wt.% addition of functionalized monolayer graphene addition in thermoplastic polyurethane matrix. Further, it is observed that 3 wt.% of functionalized monolayer graphene-reinforced thermoplastic polyurethane nanocomposite results in minimum coefficient of friction (0.42) and abrasion rate (19%) under constant normal load (5 kcal/mol/Å) and maximum sliding velocity (11 m/s). However, further reduction in minimum values of coefficient of friction and abrasion rate at 3 wt.% of functionalized monolayer graphene-reinforced thermoplastic polyurethane nanocomposites is seen under the minimum sliding velocity (1 m/s) considered with the same normal load condition. Finally, the inherent mechanisms for enhancement of tribo-mechanical properties in functionalized monolayer graphene-reinforced thermoplastic polyurethane nanocomposites are analysed by the atomic density profile, free volume and Connolly surface at the atomic level.