Polyethylene glycol (PEG) is expected as a biodegradable oil for stern tubes. In this study, its tribochemichal reaction with calcium lactate additives was examined. It was found that the friction coefficient PEG oil with calcium lactate additives was a little bit of lower than only PEG oil. Surface and lubricant oil were analyzed by Raman spectroscopy and XPS. Analysis results revealed that the iron oxide on plate surface decreased and that in the lubricant oil increased by calcium lactate additives.
