Chemically expanded graphite (CEG) has recently been identified as promising reinforcement for polymer composites with the ability for commercial up-scaling. In this work, silane and polydopamine functionalized CEG were successfully synthesized and employed to prepare ultra-high molecular weight polyethylene (UHMWPE) nanocomposites with an enhanced interfacial compatibility. Characterisation of the functionalized CEG indicated a significant oxygen reduction, which gave rise to a restoration of the graphitic structure. The polydopamine functionalized CEG showed an enhanced exfoliation and dispersion in organic solvents and the polymer matrix with respect to the non-modified CEG. The silane functionalized CEG provided a higher affinity towards the matrix with polymer chains covering the CEG sheets on the fracture surfaces. The addition of functionalized CEG enhanced the mechanical properties of the UHMWPE matrix with an increase in micro-hardness of up to 25% and storage modulus of up to 58%. Furthermore, the hydrophobicity of the composites was significantly enhanced with an increase in water contact angle from 98.6° for the pure polymer to 119° for 5 wt% silane functionalized CEG. Preliminary wear experiments indicated the potential of the composites for tribological applications with a decrease in wear rate of up to 99% under water lubricated conditions.