Comparison of solid substrates to differentiate the lubrication property of dairy fluids by tribological measurement

• Tribology property of a lubricant is affected by physical properties of the substrate.
• The substrate properties include wettability, stiffness and surface roughness.
• Some tribology tests cannot be explained by the property measured in static condition.

Three popular solid substrates (surgical tape, silicone rubber and EPDM rubber) were investigated to examine the lubrication properties of water, aqueous protein solution (3.9% solids), skim (0.1% fat) and full fat (3.8% fat) milk samples with reference with their dry contacts. It was observed that the tribological properties of the test fluids were greatly affected by the physical properties of the solid substrates, particularly wettability. Surgical tape surface, having similar wettability and surface roughness to the surface of the human tongue, appeared to be the best substrate for tribological investigations because of its ability to differentiate dairy solutions with different compositions. Silicone rubber and EPDM rubber, on the other hand, showed the same friction for all the dairy fluids and were thereby not suitable for this tribology test. For very hydrophobic surface like EPDM rubber, the tribological result is governed by the entrapment of air pockets between the solid substrate and the test fluid; therefore, it cannot be explained solely by its physical properties measured in static condition.