Surface modification of synthetic montmorillonite as thickener: rheological behavior and tribological properties at high load and high temperature

Organic montmorillonite, a typical clay mineral, has been used as a high temperature grease thickener. Although naturally occurring montmorillonite (MMT) is commercially available, a readily synthesizable alternative is needed to achieve uniform elemental composition and controllable physical and chemical properties. Synthetic MMT with a crystal structure similar to that of naturally occurring MMT was prepared by a one-step hydrothermal method. Different organic MMT samples were subjected to alkyl chain intercalation by dodecyl trimethyl ammonium chloride, tetradecyl trimethyl ammonium chloride, cetyl trimethyl ammonium chloride and octadecyl trimethyl ammonium chloride (OTAC-MMT). Synthetic MMT greases were prepared using the four alkyl chains intercalated organic MMT samples as thickeners. Due to the longest alkyl chain of OTAC, OTAC-MMT with the smallest particle size had the most different arrangement of interlayer molecules, the largest basal spacing, the highest hydrophobicity and the highest organic content. The rheological behaviour and tribological results showed that OTAC-MMT grease had the best mechanical stability, colloidal stability and thermal stability among the four synthetic MMT greases. In addition, OTAC-MMT had stable and good anti-wear and anti-friction properties under high temperature and high load conditions. This study is expected to promote the expansion of synthetic MMT applications in grease manufacturing and related potential applications in the near future.