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

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