Environment-friendly polymeric boundary lubricants for mechanical bearing systems

Abstract

Every mechanical system has sliding components which experience friction and if proper lubrication is not provided, the component will wear and this will eventually lead to failure. Reducing friction and wear will further help in conserving energy. The current methods of lubrication for many contacting surfaces in mechanical systems are the use of protective hard coatings on surfaces and the use of lubricants added with appropriate additives. Commonly used additives in the lubricants are ZDDP (zinc dialkyl dithiophosphate) and MoDTC (molybdenum dialkyl dithiocarbamate) etc. However, the additives used in the lubricants are a major source of air pollution which causes health hazards and contributes to global warming. Hence, there is a greater need to modify the lubrication strategies where the use of lubricant additives is reduced or fully eliminated. Therefore, the present research strategy is developed with one major goal: To provide energy saving and environmental-friendly lubrication method whereby to fully eliminate the use of harmful additives as well as reduce the amount of lubricants needed. Lately, polymers have been used as protective coatings in many applications due to their low production cost, ease of deposition onto intricate shapes and good corrosion resistance. The present study focuses on exploring the feasibility of using polymer films as micro-boundary lubricant layers onto metallic substrates modified with appropriate surface pre-treatments, which are expected to enhance the lubrication characteristics and reduce the consumption of harmful additives and the amount of lubricants in sliding mechanical components. Mainly three approaches are explored: (1) Air-plasma pretreatment of the substrate to improve the adhesion between the polymer film and the substrate (2) development of nanocomposite polymer films; (3) overcoating an ultra-thin layer of perfluoropolyether (PFPE) onto the nanocomposite polymer film for achieving high wear durability under dry and base oil (lubricant without any additives) lubricating conditions. Ultra high molecular weight polyethylene (UHMWPE) is the selected polymer and single walled carbon nanotubes (SWCNTs) are used as nano filler reinforcements in this study for developing the nanocomposite film. Mechanical, thermal and tribological characterization of the developed nanocomposite film is performed. Effect of temperature, counterface material and the UV radiations on the tribological performance of the nanocomposite film is also evaluated. It is observed that the addition of SWCNTs to the UHMWPE polymer film improved the wear durability of the film significantly under dry and base oil lubricated conditions.