Response surface methodology for eicosanoic acid triboproperties in castor oil

Response surface methodology with Box–Benhken (BB) design of experiment is utilized to study the antiwear (AW) and lubricity properties of eicosanoic acid in biodegradable castor oil base-stock and the results were compared with those of zinc dialkyldithiophosphate (ZDTP) and octadecanoic acid. The designs utilize load, additive concentration and temperature to develop models for the antiwear and lubricity response in a four-ball configuration. This was done by performing statistically designed experiments, estimating the coefficients in the mathematical models, predicting the response, checking for adequacy of the model and response optimization. Comparison of predicted and experimental response values outside the design conditions and for the optimal wear conditions showed good correspondence, implying that empirical models derived from response surface approach can be used to describe the tribological behavior of the additives in castor oil base-stock. Eicosanoic acid showed good tribological properties comparable to the popular octadecanoic acid and ZDTP lubricant additives, without acidic corrosion phenomenon as in ZDTP.