Rheology of lubricating greases modified with reactive NCO‐terminated polymeric additives

Abstract

A comprehensive rheological characterization of lithium lubricating greases modified with NCO-terminated polymers has been performed in this work, with special emphasis on the effect of temperature. With this aim, NCO-terminated polymers were prepared from several di-and tri-functional polyols and polymeric MDI. Afterwards, the reaction between terminal isocyanate groups and 12-hydroxystearate lithium soap, used as thickener for lubricating grease formulations, was promoted. Transient and steady-state viscous flow, rheodestruction and stress relaxation tests were performed on the different samples studied. In this sense, the influence that temperature, free NCO content, molecular weight, and functionality of the reactive polymers exert on the rheological response of lubricating greases was analyzed.The most important rheological modification was achieved by using the lowest molecular weight polymer. In general, NCO-terminated polymers significantly dampen the influence of temperature on the rheological functions of the additive-free lubricating grease. In some cases, the viscosity and/or viscoelastic functions even increase with temperature, especially in formulations with residual free NCO groups. Several experimental flow problems, such as fracture and sample expelling from the measuring tool, are generally found, more frequently in formulations with high NCO content.

Design of lubricating grease formulations using recycled polypropylene from postconsumer films as thickener agent

“…Figure 5 shows polymer/oil gels viscous flow curves as a function of recycled polymer concentrations. 15,23 Sisko's model fits this flow behavior fairly well (R 2 > 0.995): where m is a parameter related to the consistency of the sample, n is the slope of the shear thinning region, and g 1 is the highshear rate-limiting viscosity. Shear rates larger than those shown in Figure 5 produce the fracture and/or sample expelling, as previously reported.…”

Linear and nonlinear viscoelasticity of oleogels based on vegetable oil and ethylene vinyl acetate copolymer/isotactic polypropylene blends

“…This time‐strain factorability has been previously used for entangled polymer systems, lithium lubricating greases modified with reactive polymers or oil‐in‐water emulsions . The damping function is a rheological parameter that can be used to evaluate the structural resistance of oleogels under shear, although, in this case, at constant applied strain.…”

Tribological behaviour of novel chemically modified biopolymer-thickened lubricating greases investigated in a steel–steel rotating ball-on-three plates tribology cell

“…Figure 2 shows the comparison at 25 ºC, which reveals very similar viscosity values, excepting for sample CH which is more viscous in all the shear rate range studied. Shear rate range is limited due to the appearance of fracture at high or moderate shear rates [43][44][45], which is favoured with 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 8 grooved measuring surfaces [46]. Resulting flow curves can be satisfactorily described by the well-known power-law model: (1) where K and n are the consistency and flow indexes, respectively.…”