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Metal cutting fluids (MCFs) or cutting fluids are widely applied industrial products traditionally based on hydrocarbons. However, hydrocarbon-based cutting fluids have low thermal stability and tend to vaporize during application, causing environmental and human health problems. One of the most promising cutting fluids is based on vegetable oils, due to the high level of biodegradability and low toxicity, although vegetable oils have unsaturations that reduce their oxidation stability. This work evaluated the thermal and rheological behaviors of two chemically modified cottonseed oils: epoxidized fluid and hydroxylated fluid, besides unmodified cottonseed oil and commercial cutting fluid. The thermogravimetric analysis showed that the commercial cutting fluid starts volatization at low temperature (100°C) while all cutting fluid derivatives of cottonseed oil have thermal resistance higher than 300°C under inert atmosphere. All cutting fluids had Newtonian behavior (power-law index = 1), with viscosity up to 0.12 ± 0.05 Pa s. The small differences indicate similar lubricity. As expected, the viscosity decreased with temperature for all fluids. The apparent activation energies decreased in the order commercial cutting fluid [ epoxidized fluid [ cottonseed oil [ hydroxylated fluid. Lower apparent activation energy of hydroxylated fluid indicated better heat transfer of this fluid due to better convection. Real drilling experiments indicated lower tool wear with the use of the epoxidized fluid.

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