ASTM D7373 Predicting Biodegradability of Lubricants Using a Bio-kinetic Model
A biodegradable substance is one which is broken down into smaller molecules by microbes. This test is intended to predict the amount of a lubricating oil that will biodegrade in a specified period of time, typically 28 days.
Traditional tests to predict biodegradability include ASTM D5864, ASTM D6139 and ASTM D6731. All three of these tests add microorganisms to the lubricant and follow the production of carbon dioxide as the lubricant breaks down. The amount of CO2 produced is used to calculate the amount of sample that has biodegraded. These tests take a month to run and have the inherent difficulties and variability of microorganism use. (Please note: Petro-Lubricant Testing Laboratories does not offer these microorganism tests).
The bio-kinetic model test offered by Petro-Lubricant Testing Laboratories does not involve microorganisms. It uses known biodegradation rates of typical base lubricants classified using chromatographic methods to predict the amount of sample that will biodegrade in 28 days.
The sample is chromatographically separated into four fractions based on polarity. Biodegradable oil components, typically polyalphaolefins and esters, elute in the first and third fractions. Using the percentage of oil in these fractions, with known biodegradation rates, the percent of oil predicted to biodegrade in 28 days is calculated and reported.
Note: This test is intended for oils. For grease samples, we will first separate the base oil from the thickener using a Koppers Extraction (ASTM D4425), and then analyze the base oil for biodegradabiltiy. Extracted oil may not give results equivalent to neat base oil because of oil soluble components in the extracted portion not otherwise present in the neat base stock.