Studies on competitive interactions and blending order of engine oil additives by variable temperature 31P-NMR and IR spectroscopy

Interactions between various engine oil additives including dispersant, detergent, antiwear/antioxidant, and viscosity index improvers have been investigated through changes in the P-31- NMR and IR spectra. Significant changes in the P-31-NMR and IR spectra of zinc dialkyldithiophosphere (ZDDP) have been observed by varying the blending order of additives. Dispersant-detergent (polyisobutylene succinimide-calcium overbased sulfonate) and viscosity index improver-detergent (dispersant olefin copolymer-calcium overbased sulphonate) interactions were found to be strong and irreversible in nature. Variable temperature P-31-NMR spectra have provided enough evidence to suggest that the actual performance of an additive may riot be decided by its bulk interactions with other additives at room temperature, and that tribochemical reactions occurring at higher temperature play a greater role.