Formulation and evaluation of emulsifier systems for petroleum- and bio-based semi-synthetic metalworking fluids.

Abstract

Metalworking fluids (MWFs) are essential to manufacturing for cooling and lubrication. Most MWFs are oil-in-water emulsions that pose human and environmental hazards throughout their life cycle. One strategy to reduce these hazards is to optimize MWF formulations for long-term emulsion stability under typical field conditions including hardwater. Fundamental research to quantify relationships between the physiochemical properties of MWF emulsifier systems, emulsion stability in hardwater, and MWF performance has been limited. This research evaluates the effectiveness of common commercial emulsifier systems to maintain emulsion stability under hardwater conditions. The results indicate that increasing cation concentration and charge results in increasing emulsion sizes and decreasing zeta potential where monovalent cations have little impact on emulsion destabilization while higher charge cations have a significant impact. Given the ineffectiveness of these emulsifier systems to maintain emulsion stability in hardwater, an investigation into the design of emulsifier systems for improved hardwater stability was conducted. This investigation quantifies the impact of emulsifier system properties on hardwater stability. Results from 2500 formulations indicate that the use of a twin-headed anionic surfactant can provide improved hardwater stability for both petroleum- and bio-based formulations. The machining performance of MWF formulations based on the new emulsifier systems was compared to commercial MWFs. Machining performance was evaluated by a new method designed to minimize sources of variability and to correlate with expected field performance. Results from machining performance tests indicate that the MWFs designed for hardwater stability are competitive with current MWF products. Since both petroleum- and bio-based MWFs were successfully formulated for hardwater stability, an analysis of the life cycle energy and emissions was conducted for three end of life handling strategies (disposal, oil recycling, oil incineration) to support feedstock selection decisions. The results suggest that there is a trade-off between emissions categories and energy consumption depending on MWF feedstock. This analysis also demonstrates the oil reclamation for reconstitution as MWF most favorably reduces MWF life cycle emissions and energy consumption. These results can be used to minimize MWF life cycle emissions and energy consumption through informed feedstock selection and the design of emulsifier systems for long-term stability in hardwater.