Using an electronic microbalance technique to study the stick–slip behavior of lubricated polypropylene fibers

By use of an electronic microbalance, fiber/fiber friction measurements were made on cleaned and lubricated polypropylene (PP) filaments. The filaments were coated with a 0.14‐μm‐thick layer of one of the five lubricants: two different hydroxylated oils (hydroxylated oleate and hydroxylated stearate) and three different ethoxylated surfactants [(i) ethoxylated 10 OE dioleate; (ii) ethoxylated 15 OE dioleate; and (iii) ethoxylated 20 OE trioleate]. Despite the thick layer of lubricant applied, stick–slip persisted. Theoretical considerations of experimental conditions (load, speed, and viscosity) show that the pressure is very high at the contact point, and this would induce film thinning and thus stick–slips arising from phase transitions. Statistical evaluations and atomic force microscopy images show that contacts between PP surfaces take place in presence of lubricants because surface asperity heights are larger than the lubricant film thickness. Oils or surfactants having similar surface tensions give different interfiber cohesion. Some explanations correlating the lubricant chemical structure and its spatial conformation, as well as its capacity to form intermolecular bonds and associative organization, to interfiber friction are given.