Tribological study of epoxide-functionalized alkali lignin-based gel-like biogreases

The frictional and wear properties of novel bio-based greases consisting of epoxide-functionalized alkali lignins (EALs) dispersions in castor oil were examined. EALs used as thickeners were obtained by chemical modification of alkali lignin (AL) with poly (ethylene glycol) diglycidyl ether (PEGDE). The thickener concentrations and epoxy indices used spanned the ranges 2.5–10 wt% and 0.28–0.79 mol/kg, respectively. The influence of both variables on friction and wear was studied. Comparing the frictional behaviour of the biogreases and the base oil revealed that the influence of the thickener on lubrication performance differed with temperature, load, and sliding velocity. The thickener effectively reduced friction and wear, but especially at low concentrations (5 wt% or lower) and high epoxy indices (up to 0.79 mol/kg).