Test methods under the auspices of ASTM Committee E37 on Thermal Measurements are being developed for determining the oxidative induction time (OIT) of hydrocarbons by differential scanning calorimetry (DSC) and pressure DSC. This test method,ASTM E1858, is applicable to hydrocarbons, for example, polyolefins and motor oils that oxidize exothermically in their analyzed form. The DSC method is used at ambient pressure, one atmosphere oxygen. The pressure DSC (PDSC) protocol is used at high pressure, 3.5 MPa or 500 psig, oxygen. The test specimen and reference aluminum pan are heated to a specific temperature, DSC at 195°C and PDSC at 175°C in an oxygen environment. Heat flow out of the specimen is monitored at the isothermal temperature until the oxidative reaction is manifested by heat evolution on the thermal curve.
Statistically designed experiments aided in establishing the factors affecting the OIT. Sample pan type, pressure, temperature, and oxygen flow rate were observed as significant experimental parameters. The OIT is a relative measure of oxidative stability at the test temperature. A precision and bias statement has been developed by ASTM Committee E37 and is reported based on a recent national round robin.