Durable electroless deposited Ni-P films on NBR for dynamic contacts. Characterization and tribological performance

Abstract

In this paper we present a green method to deposit a low-friction Ni-P film on nitrile butadiene rubber (NBR) for dynamic contacts. NBR's surface functionalization was carried out, where metal bonding carboxylic acid derivatives were created as a consequence of aqueous chlorination. The modified surfaces were thereafter activated with silver nanoparticles (Ag-NBR) or catechol moieties following polydopamine polymerization and reduction (PDA-NBR). Furthermore, relevant physical and mechanical alterations were observed, namely surface fissures and a decrease of tensile strength of 43% and an increase of Young's Modulus by +132%. Nevertheless, the sealing ability of the rubber may not have been significantly affected as compression set was reduced by a fairly 20%. Thereafter, a low friction Ni-P film was deposited on the functionalized and activated samples via electroless plating. PDA-NBR plated NBR displays a smooth, cauliflower morphology Ni-P film whereas in Ag-NBR substrates the film has a granular feature resulting from a hierarchical structure. The Ni-P film adhesion to Ag-NBR and PDA-NBR surfaces were 0.7 ± 0.2 MPa and 1.5 ± 0.3 MPa, respectively. Tribological evaluation demonstrated that the coefficient of friction decreased from ~1.16 of NBR to a lower and steadier value for PDA-NBR than its Ag-NBR counterpart: 0.60 and 0.50 against 0.73 and 0.76 for 3 N and 5 N loads, respectively. These results show that the rubber activation treatment influences the microstructure of the deposited Ni-P film and its tribological behavior.