Rheology and microstructure of lithium lubricating greases modified with a reactive diisocyanate-terminated polymer: Influence of polymer addition protocol

Moreno, G.; Valencia, C.; de-Paz, M.-Violante; Franco, J.M.; Gallegos, C.

doi:10.1016/j.cep.2006.11.006

Cited by 19 publications

(18 citation statements)

References 17 publications

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“…They used the non-contact mode to successfully examine nonwashed samples, although some discrepancies in both types of observations were detected. However, suitable microstructural observations were previously obtained with lithium greases by using the tapping mode, once the sample was heated up to a temperature below the dropping point and, then, cooled down to room temperature in order to obtain a very smooth surface [16,17]. This protocol was followed in this study.…”

Section: Afm Observationsmentioning

confidence: 99%

“…In spite of some experimental difficulties, this technique provides a great advantage. Thus, grease samples do not need to be perturbed to carry out suitable microstructural observations [16,17], since the experiments can be performed under atmospheric pressure. In this paper, different microstructures presented by a set of commercial and model lubricating greases were examined using the AFM technique.…”

Section: Introductionmentioning

confidence: 99%

“…The most common criticism associated to SEM or TEM observations is that both techniques are vacuum based, and grease sample has to be submitted to either a freezing treatment or oil removing, thus distorting the original microstructure. Up to now, little work has been carried out on the characterisation of grease microstructure by means of atomic force microscopy (AFM) [15][16][17]. In spite of some experimental difficulties, this technique provides a great advantage.…”

Section: Introductionmentioning

confidence: 99%

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Atomic Force Microscopy and Thermo-Rheological Characterisation of Lubricating Greases

et al. 2010

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In this work, non-perturbed microstructures of several commercial and model lubricating greases, differing in nature and concentration of the thickener agent, were examined using the atomic force microscopy (AFM) technique. Grease microstructure mainly depends on the nature of the thickener employed and, also, on thickener concentration and viscosity of the base oil. Thermal-induced changes in the viscoelastic response of lubricating greases have been investigated by using different rheological techniques in a temperature range of 0-175°C. Small-amplitude oscillatory shear (SAOS) measurements were carried out to determine the mechanical spectra of the different samples studied. Lubricating grease rheological thermal susceptibility was analysed by following the evolution of the plateau modulus with temperature. SAOS functions dramatically decrease, in most cases, above a characteristic temperature, which depends on nature and/or concentration of the thickener used and therefore on grease microstructure. The thermo-mechanical reversibility of grease microstructure has been studied by carrying out triple-step-shear stress tests (shear stresses inside and outside of the linear viscoelasticity range), at different temperatures. The degree of lubricating grease non-reversible structural breakdown, which increases with temperature, depends on the shear stress applied above the linear viscoelasticity limits.

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Section: Afm Observationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Atomic Force Microscopy and Thermo-Rheological Characterisation of Lubricating Greases

et al. 2010

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“…Furthermore, recent advances in AFM have enabled highspeed imaging of soft samples allowing the direct visualization of biomolecules [24,25]. So far, some specific observations of grease microstructures by means of atomic force microscopy have been previously reported [12,15,18,[26][27][28][29]. However, it still remains difficult to image the nanoscale topography of lubricating grease samples by AFM, because some artifacts can arise due to non-desired interactions between the tip and the sample as a consequence of several factors such as tip geometry, lateral forces or grease textural and rheological properties.…”

Section: Introductionmentioning

confidence: 99%

“…In this sense, Hurley and Cann [11] were not able to obtain good observations in non-washed samples using the contact mode. Some of these problems can be avoided by heating the grease sample below the dropping point and then cooling down to obtain smooth enough films [18,26,27]. However, this pre-heating protocol must be also optimized to avoid any change in the thickener-oil interaction balance.…”

Section: Introductionmentioning

confidence: 99%

AFM and SEM Assessment of Lubricating Grease Microstructures: Influence of Sample Preparation Protocol, Frictional Working Conditions and Composition

2016

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The microstructure of lubricating greases greatly conditions their in-service performance. In that sense, optimal testing protocols are required in order to accomplish their correct morphological characterization. This study explores and compares the suitability of Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) techniques for imaging six different commercial metallic soap-based greases and two novel biopolymer-based formulations. Pros and cons of both techniques as well as the effect of sample preparation protocol were analyzed. The results revealed a wide variety of morphological characteristics depending on composition. Thus, the four anhydrous calcium-based greases demonstrated two clearly distinct microstructures (fibrous and granular) determined by the type of base oil employed. With regard to the lithium complex greases, the typically reported microstructure characterized by welldefined entangled and fibrous network was observed in both AFM and SEM techniques.As for the two biopolymer-based greases, fiber networks were also encountered.Besides this, selected greases were subjected to different tribological tests, and the effect of high-shear frictional working treatments on their microstructure was also analyzed. As a result of the friction and internal wear, the AFM results evidenced microstructural changes which depended on grease composition. Overall, the combined use of AFM and SEM techniques was demonstrated to be a powerful approach to microstructurally characterize lubricating greases.

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

Moreno

Franco

Valencia

et al. 2010

J of Applied Polymer Sci

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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.

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Rheology and microstructure of lithium lubricating greases modified with a reactive diisocyanate-terminated polymer: Influence of polymer addition protocol

Cited by 19 publications

References 17 publications

Atomic Force Microscopy and Thermo-Rheological Characterisation of Lubricating Greases

Atomic Force Microscopy and Thermo-Rheological Characterisation of Lubricating Greases

AFM and SEM Assessment of Lubricating Grease Microstructures: Influence of Sample Preparation Protocol, Frictional Working Conditions and Composition

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

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