Synthesis and testing of eco-friendly, non-toxic cutting fluid emulsions

Abstract

The evolutions in the development of metal working fluid (MWF) from petroleum based products have brought remarkable changes to the present growing machining industry. The established MWF/Cutting fluids have reduced the machining time and increased tool life resulting in economic profits. Even though the use of petroleum oil based cutting fluid have on one side made a significant contribution to the present industry, it has on the other side have exponentially accelerated the rate of environmental pollution. Commercial Cutting Fluids (CCF) generally synthesized using mineral oil or its derivatives, are mostly highly toxic and detrimental to the health of the workers. Furthermore, unregulated and unethical disposal of used cutting fluids by industries would create an environmental disaster. This is due to the difficulties in handling and disposal of degraded or toxic used cutting fluid. Hence, there is an urgent need for the development of an alternative, sustainable, non- toxic and completely bio-degradable cutting fluid to replace the mineral oil based cutting fluid. Thus the need of the hour for an alternative base oil has made tribologists think of vegetable oil-based cutting fluids. Among vegetable oils, coconut oil has superior inherent tribological properties such as low coefficient of friction, high resistance to wear and higher thermal stability characteristics when compared to other vegetable oils. In the present work, a Green Cutting Fluid (GCF)/metal cutting fluid emulsion is developed from coconut oil using non-toxic emulsifiers and additives. Further, sustainability of the developed cutting fluid was considered and processes were selected to follow closed loop philosophy and its properties were compared to CCF of the same grade. The properties of the cutting fluid were evaluated as per standard test procedures. Emulsion stability was evaluated using Dynamic Light Scattering (DLS) equipment by measuring particle size and zeta potential, pH measurement and oven tests. All the ingredients added to make the green cutting oil was tested for toxicity following Organisation for Economic Cooperation and Development (OECD-203) acute fish toxicity test procedure. Toxicity evaluations of fresh and used metal working fluids were carried out using Fish Embryo Test- FET (OECD-236) and Skin cell viability studies to study the effect of cutting fluids in aquatic system and human skin respectively. Anti-corrosion characteristics of cutting fluid samples were evaluated as per guidelines of American Standard for Testing Materials (ASTM) D4627 standard and in house developed weight loss method. Bacteriological analysis of GCF and CCF was carried out using different culture and plating techniques. Biochemical Oxygen Demand (BOD) test and Chemical Oxygen Demand (COD) test has been carried out to evaluate biodegradability aspect of GCF and CCF. The machining capability of the newly formulated metal cutting oil emulsion was studied through drilling and turning experiments. Further, the study covers testing of the cutting fluids using the novel tool-chip-tribometer and development of a novel lathe tribometer setup that can render friction value in-situ of newly generated surfaces during machining. The results procured from emulsion stability test, toxicity test, tribological test, antibacterial test, biodegradability test, corrosion test and machining test infer coconut oil based cutting fluid to have competent properties compared to CCF. Thus, the newly developed cutting fluid from coconut oil is a potential alternative for commercially available metal working fluid.