Sustainable production of high-performance bio-based hydraulic fluids from vegetable oils: Recent advances, current challenges, and future perspectives

The significant benefits of sustainability, biodegradability, and non-toxicity have led to a dramatic increase in the utilization of vegetable oil-based hydraulic fluids across various industries. Therefore, knowing how to formulate biobased high-performance hydraulic fluids for industrial application with various types of base oils (e.g., petroleum-based oils, esters, complex esters, and estolides) and their essential physical and chemical properties are the key factors. This review introduces complete information of different petroleum base oils and provides an overview of the most important performance indexes of high-performance hydraulic fluids, and the most important esters used as base stocks in hydraulic fluids. Recent advancements in chemical modification of vegetable oils as one of the most popular methods to achieve an ideal base oil for the formulation of high-performance hydraulic fluids and two examples of estolide esters and epoxidized vegetable oils are extensively reviewed. Moreover, methods for converting vegetable oils into esters with enhanced stability and fluidity are discussed, offering new avenues for utilizing bioresources and promoting green chemistry. Furthermore, current challenges and future perspectives on the production of high-performance vegetable oil-based hydraulic fluids are discussed.