Viscosity properties of mineral paraffinic base oils as a key factor in their primary biodegradability

The primary biodegradability of two types of paraffinic base oils (solvent and catalytically dewaxed oils) and their blends was evaluated using the CE C L-33-A-93 test. The biodegradability values varied between 10% and 75%. B ase oil mixtures displayed varying contents in aromatic and polar compounds and a wide range of kinematic viscosity (KV) values, from roughly 10 to 60 0 cSt (at 40 degreesC), while their viscosity indices were almost constant (90-100). The biodegradability of oils was closely related to their content in polycyclic aromatic hydrocarbons and was also decreasing with kinematic viscosity. For the two types of base oils, a linear relationship could be set between the biodegradation percentages and the logarithms of KV values. These results show that, beside overall chemical features such as the cont ents in aromatic compounds, KV may be a prominent parameter for assessing t he primary biodegradability of mineral base oils.