Self-lubricating, wear resistant protic ionic liquid-epoxy resin

A new self-lubricating, wear resistant epoxy resin material (ER+DCi) has been obtained by addition of a 9 wt% of the room-temperature protic ionic liquid (PIL) tri-[bis(2-hydroxyethyl)ammonium)] citrate (DCi) to the mixture of the prepolymer and the hardener composed of a mixture of amines. The highly polar tricationic protic ammonium carboxylate ionic liquid shows a high contact angle on the resin surface and distributes inside the epoxy matrix as spheres of around 50 µm in diameter, with a mean density of approximately 38 mm^sup 2^. The presence of the ionic liquid fluid phase inside the cavities has been determined by scanning electron microscopy (SEM) observation of fracture surfaces and Fourier transform infrared spectroscopy (FTIR)-microscopy. The DCi phase reduces the residual curing enthalpy and the glass transition temperature, as determined by DSC, without significantly changing microhardness or electrical resistivity values. Dynamic mechanical analysis (DMA) shows that DCi reduces storage modulus, loss modulus and tan δ values. The tribological performance of the new material has been compared with that of the neat epoxy resin under pin-on-disc sliding conditions. ER+DCi shows more than 50% reduction of the friction coefficient with respect to neat epoxy resin, and a polished surface, in contrast with the severe wear that takes place in the case of neat epoxy resin. A self-lubrication mechanism by release of the ionic liquid lubricant under load is proposed.