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The Thermal Stability of Bio-Oils, Biobased Oils and Biolubricants

According to ASTM’s publication Guide to ASTM Test Methods for the analysis of petroleum products and lubricants, 2nd Edition (2007), the thermal stability characterizes physical and chemical property changes that may affect an oil’s lubricating performance. The ASTM D2070 method is designed to test the thermal stability of oils by heating oil in the presence copper and steel rods at 135 ˚C (275 ˚F) for 168 hours.

A slightly modified approach was used to study bio-oils: while same sample preparation and heating in the presence of Cu and Fe rods were maintained, small oil samples were extracted every 24 hours for the duration of the experiment and analyzed by ASTM D6186.  Polnox 8020 shows consistent, superior performance from Day 0 to Day 7, as illustrated in Figure 1. Indeed, The oxidative stability of the oil treated with 2% Polnox® 8020 that was exposed to heat at 135 ˚C for 4 days in the presence of Cu and Fe is equivalent to oil treated with 2% commercial AO that was not exposed to heat, Cu, or Fe catalysts.

The Polnox- and commercial AO-treated oil samples were analyzed by various ASTM methods to measure their thermo-oxidative stability (OIT), change in total acid number (δTAN), and kinematic viscosity (δKV), as illustrated in Figure 2.  Dramatically increasing the thermo-oxidative stability of oil subjected to heat, oxygen in air, and pro-oxidant catalysts like copper and iron, Polnox® 8020 demonstrates remarkable protection capability compared to the commercial AO.

Figure 2:  Performance Comparison on 4th Day Sample
(Heated at 135 ˚C in the Presence of Cu and Fe Rods)

Figure 1:  Biolubricant Oil Exposed to Heat and Cu and Fe Rods

ASTM D2070 Test at 135 ˚C



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