Room Temperature Production of Polyurea-Based Lubricants: Using L-Serine Derivatives, 1,5 Pentamethylene Diisocyanate, and a Planetary Ball Mill

In this work, we produced a new polyurea (PU)-based thickener based on serine derivatives (ethanolamine or L-Serine ethyl ester) and 1,5 pentamethylene diisocyanate (PDI), using castor oil as base oil and methylene diphenyl diisocyanate (MDI) as a reference. Polymerization was carried out in a planetary ball mill at room temperature for 75 min. The polymerization degree of the PU thickener was examined via 1H NMR, which ranged between 1.8 and 14.6 repeating units after the extraction of the base oil. Rheological analysis showed gel formation for ten out of twelve samples, which was strongly dependent on the polymerization degree and thickener amount. The decomposition temperature of the MDI-based PU greases was consistently roughly 20 °C higher than that of PDI-based systems. The lubricants were further evaluated through rheology experiments before and after the gels underwent an annealing process at 100 °C for 1 h (amplitude and frequency test), indicating a strong increase in the storage modulus G’, whereas the yield point γF remained constant or decreased.