Stability of oil-based dispersions containing poly(tetrafluoroethylene) micropowder

• Oil-PTFE-cc dispersions were prepared and their stability analyzed.
• Differences are discussed in terms of particle interactions and stability.
• Concentration of functional groups can be explained by the amount of the zeta potential vs. pH.
• The influence on tribological properties is discussed as well.
• An individual optimum level for both PTFE micropowders in the oil can be derived.

Micropowder of poly(tetrafluoroethylene) (PTFE) can be used in base oils to improve the tribological properties significantly, if oil molecules are covalently linked to primary PTFE particles in the dispersion. Enhanced properties are not only determined by the amount of PTFE micropowder added to the oil but as well by the surface charge, radical concentration, and the size and distribution of PTFE particles in the oil phase.The chemical compatibilization (=cc) between PTFE micropowder and ester oil by the use of two types of PTFE micropowder, which differ in radical concentration and the amount of functional groups is shown. The concentration of PTFE micropowder in the dispersions was varied from 5 to 20 wt%. Both the pure PTFE micropowder and the oil-PTFE-cc dispersions were characterized by ESR and FTIR spectroscopy as well as by zeta potential measurements. Rheological and tribological tests were performed on the ester oil and the oil-PTFE-cc dispersions. Qualitative differences are discussed in terms of particle interactions, dispersion stability, chemical compatibilization efficiency and the amount of functional groups.A correlation between flow properties and surface charge of the PTFE particles within the dispersions was obtained. The influence on tribological properties is discussed as well.

Stabilization of oil-PTFE-cc dispersion can be achieved by shearing the perfluoroalkyl(peroxy) radicals on the PTFE particle surface (1) and the subsequent reaction with olefinic oil molecules (2) (additional stabilization by negative charges due to functional groups and by the shearing process itself (3).Figure optionsDownload as PowerPoint slide