Chemically expanded graphite-based ultra-high molecular weight polyethylene nanocomposites with enhanced mechanical properties

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.The authors would like to acknowledge the support from M. Larsson by performing the Raman measurements. The research is financially supported by Vinnova as part of the SIO Grafen programme (reference number: 2017–03609). G.G. gratefully acknowledges the Portuguese Science Foundation (FCT) for Programme Stimulus of Scientific Employment–Individual Support (CEECIND/01913/2017) and financial support of TEMA by the projects UIDB/00481/2020 and UIDP/00481/2020; and CENTRO-01–0145-FEDER-022083–Centro Portugal Regional Operational Programme (Centro 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund. Finally, the authors would like to acknowledge the financial support via the 3D - PRINTGRAPH project (Grant agreement ID: 705875).With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe