Tailoring the tribological performance of SPEEK by sulfonation degree under water lubrication

Polyether ether ketone (PEEK) is a high-performance engineering polymer suitable for water lubricated bearings. However, some modifications are imperative due to its poor tribological performances in aqueous solutions. Herein, a novel sulfonated polyether ether ketone (SPEEK) was synthesized through nucleophilic condensation reaction with well-controlled sulfonation degree. The impact of sulfonation degree on surface hydrophilicity, mechanical strength, and tribological properties of SPEEK was thoroughly investigated. Among them, SPEEK-gamma with a sulfonation degree of 2.44 mol% exhibited superior tribological performance. Compared to neat PEEK and Thordon SXL, it showed a reduction in coefficient of friction (COF) by 33.7 % and 39.3 %, respectively, as well as a decrease in wear rate by 54.2 % and 97.8 %, respectively. The exceptional tribological properties of SPEEK-gamma can be attributed to the adsorption of hydrated Na+ cations facilitated by sulfonic acid groups (-SO3-), leading to hydration lubrication at the counterface interface while also enhancing intermolecular forces within the polymer matrix through sulfonic acid groups (-SO3-) presence. Consequently, SPEEK-gamma exhibits great potential as an underwater equipment material due to its excellent tribological properties under water lubrication conditions.