Analysis of the Influence of Contaminants on the Biodegradability Characteristics and Ageing of Biodegradable Hydraulic Fluids

Abstract

Ongoing concerns regarding environmental protection encourage further research aimed at the development of environmentally-friendly products. Certain research activities and industrial applications have broken the paradigm of using mineral oil for hydraulic systems by providing solutions with biodegradable hydraulic fluids. Petroleum-based hydraulic fluids are not able to meet this demand due to their often toxic properties and their environmental effects. Therefore, ecologically-acceptable fluids based on natural and synthetic esters are increasingly used as pressure fluids. Knowledge of the influence of contaminants on the biodegradability characteristics and ageing of biodegradable hydraulic fluids is a prerequisite for the successful application of these fluids in hydraulic systems. Accordingly, in this study, new information obtained from commercial biodegradable fluids (hydraulic oil environmental ester synthetics (HEES)) under the influence of common contaminants (water, mineral oil, copper solid particles, and oxygen) present in current hydraulic systems has been investigated. Based on oxidation and hydrolytic stability tests, the biodegradability characteristics and ageing of biodegradable fluids are analysed, and the influence of contaminants is described. A comparison between fluid samples with different contaminants has shown that both the total acid number (TAN) and viscosity change significantly as a consequence of ageing in the presence of water and solid particles of copper, while the biodegradability characteristic was modified mainly by contamination with mineral oil.