Degradation Pattern of Polymeric Viscosity Index Improvers in Cross-Graded Engine Lubricants

Polymeric VI improvers of cross-graded engine lubricants are prone for degradation due to both mechanical and thermal shearing. However, till now, all the engine oil specifications focus only on their resistance towards mechanical degradation. In the present study, an attempt has been made to assess the extent of polymeric degradation due to thermal shearing by using some commonly employed polymeric VI improvers and their combinations. Data generated in mechanical and thermal shearing experiments has been correlated with high temperature high shear (HT-HS) viscosity data of these sheared and unsheared oils. All these findings are further augmented by comparing relative changes in their molecular weights and molecular weight distribution profile, as obtained by gel permeation chromatographic analysis of the experimental oils.