Development of reactive prepolymers with terminal NCO groups as rheology modifiers of lithium lubricating greases.
Chemical Product Design and Engineering (CPD&E)
Chemical Product Design & Engineering - Poster (CPD&E - P)
Keywords: polymer, rheology, lubricating greases, isocyanate
Lubricating greases are highly structured suspensions consisting of a thickener dispersed in mineral or synthetic oils. Particularly, lithium 12-hydroxystearate soap is the most widely used thickening agent. Greases also contain some performance additives. Among these additives, the use of polymeric materials is a common practice in the lubrication industry to modify the rheological properties of greases by reinforcing the role of the thickening agent [1,2]. The use of reactive diisocyanate-terminated polymers can be satisfactorily used as rheology modifiers of lubricating greases [3] by promoting the reaction between terminal isocyanate groups and the hydroxyl groups located in the hydrocarbon chain of the 12-hydroxystearate lithium soap. It was demonstrated that the poly (1,4-butanediol) tolylene 2,4-diisocyanate (PBTDI) with a relatively low molecular weight shows a similar effectiveness to that achieved with non-reactive polymers of much higher molecular weights.
The main objective of this work is to develop new diisocyanate-terminated prepolymers which can be potentially used as additive of greases by studying the influence of some structural parameters such as molecular weight and functionality on the rheological response of the final product. These polymers are manufactured with polyetherols and polymeric 4,4’-diphenyl methane diisocyanate (MDI). Polymers are added to grease formulation during the final cooling ramp applied in the manufacturing process [4]. The polymeric materials used and/or resulting lubricating greases were characterized by FTIR spectroscopy, differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and atomic force microscopy (AFM). The effectiveness of such additives was tested on final greases by performing small-amplitude oscillatory shear (SAOS) and viscous flow measurements as well as standardized mechanical stability tests.
Results show that the addition of reactive isocyanate-terminated prepolymers increased significantly the values of the linear viscoelastcity functions of greases. In general, the higher the polymer molecular weight, the higher this increment in SAOS functions is. However, lower effectiveness were found for greases containing the polymer with the highest molecular weight (Mw=4700) as additive. Moreover, results are highly affected by the ageing of greases. Rheological functions evolve for several months, which indicate that the kinetics of the reaction promoted is very slow.
References
[1] Al-Sammerral, V., J. Appl. Polym. Sci. 1986, 31, 1-6.
[2] Verstrate, G., Struglinski, M. J. ACS Symp. Ser. 1991, 462, 256-272.
[3] G. Moreno, C. Valencia, M.V. de Paz, J.M. Franco, C. Gallegos, Ind. Eng. Chem. Res. 45 (2006) 4001–4010.
[4] G. Moreno, C. Valencia, M. V. de Paz, J. M. Franco, C. Gallegos, Chem. Eng. Process. (2007) in press. (doi: 10.1016/j.cep.2006.11.006).
Presented Wednesday 19, 13:30 to 15:00, in session Chemical Product Design & Engineering - Poster (CPD&E - P).
