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Crispulo Gallegos - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of different polyolefins as rheology modifier additives in Lubricating Grease formulations
Materials Chemistry and Physics, 2011Co-Authors: J. E. MartÃn-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo GallegosAbstract:The purpose of the present work is to evaluate the effect that different polyolefins, used as additives in small proportions, exert on the rheological properties of standard lithium Lubricating Greases. Grease formulations containing several polyolefins, differing in nature and molecular weight, were manufactured and rheologically characterized. The influence of the type of polymer, molecular weight, crystallinity degree and vinyl acetate content has been analyzed. Small-amplitude oscillatory shear (SAOS) and viscous flow measurements, as well as calorimetric (DSC) and thermogravimetric (TGA) analysis, were carried out. In general, the addition of polymers such as HDPE, LDPE, LLDPE and PP to lithium Lubricating Greases significantly increases the values of the rheological parameters analyzed, consistency and mechanical stability. However, the use of polyolefins as rheology modifiers does not significantly affect the friction coefficient determined in a tribological contact. The crystallinity degree, mainly dependent on the nature of the polymer, has been found the most highly influencing parameter on the rheology of the Lubricating Greases studied. However, the rheological modification exerted by EVA copolymers mainly depends on the vinyl acetate content. Thus, a negative effect in both apparent viscosity and linear viscoelastic functions of Greases was obtained when polymer vinyl acetate content is higher than 28% (w/w). © 2011 Elsevier B.V. All rights reserved.
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Atomic Force Microscopy and Thermo-Rheological Characterisation of Lubricating Greases
Tribology Letters, 2010Co-Authors: M C Sanchez, Crispulo Gallegos, José M. Franco, Concepción Valencia, F. Urquiola, R. UrcheguiAbstract: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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Rheology of Lubricating Greases modified with reactive NCO-terminated polymeric additives
Journal of Applied Polymer Science, 2010Co-Authors: G Moreno, José M. Franco, Concepción Valencia, Crispulo GallegosAbstract: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, rheo-destruction 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. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
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Recycled and virgin LDPE as rheology modifiers of lithium Lubricating Greases: A comparative study
Polymer Engineering and Science, 2008Co-Authors: J.e. Martín-alfonso, Carlos Valencia, M C Sanchez, J M Franco, Crispulo GallegosAbstract:In this work, a new application for recycled low-density polyethylene (LDPE), as rheology modifier of standard lithium Lubricating Grease formulations, was studied. The effectiveness of this additive was compared with that achieved with a virgin LDPE. With this aim, both types of polymers were added to the formulation during the manufacturing process of Greases, following the same standard protocol, to reinforce the role of the thickening agent, the lithium 12-hidroxystearate. The effect that both lithium soap and LDPE concentrations exert on the rheology of Lubricating Grease formulations and its relationship with Grease microstructure were discussed. Lubricating Greases were rheologically characterized through small-amplitude oscillatory shear and viscous flow measurements. In addition to these, scanning electron microscopy observations and mechanical stability tests were also carried out. In all cases, an increase in soap concentration yields higher values of apparent viscosity and linear viscoelasticity functions. On the other hand, the values of the rheological functions obtained for recycled LDPE-based Lubricating Greases are, in general, higher than those obtained for virgin LDPE-based Grease formulations. However, the structural skeleton developed in Greases containing recycled LDPE demonstrates less resistance to severe working conditions, showing lower mechanical stability than virgin LDPE-based Grease formulations. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
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Rheology and microstructure of lithium Lubricating Greases modified with a reactive diisocyanate-terminated polymer: Influence of polymer addition protocol
Chemical Engineering and Processing: Process Intensification, 2008Co-Authors: G Moreno, M. V. de Paz, Carlos Valencia, J M Franco, Crispulo GallegosAbstract:This work deals with the influence that the addition of poly(1,4-butanediol) tolylene 2,4-diisocyanate terminated prepolymer (PBTDI) at different stages during the manufacturing process of a traditional lithium Lubricating Grease exerts on its rheological and morphological characteristics. With this aim, the reaction between terminal isocyanate groups and the hydroxy group located in the hydrocarbon chain of the 12-hydroxystearate lithium soap was intended to be promoted during Lubricating Grease processing. Several PBTDI-based Greases just differing in the process stage at which this polymer was added were prepared. The polymer used and the final Lubricating Greases were characterized by FTIR spectroscopy and DSC techniques. The effect of PBTDI addition at different processing stages was tested on final Greases by performing small-amplitude oscillatory shear (SAOS) measurements as well as atomic force microscopy (AFM) observations. Addition of PBTDI significantly increased the values of the linear viscoelasticity functions when it was added during the final cooling stage of the manufacturing process. It was demonstrated that this increment in relation to the values found for the additive-free Lubricating Grease was only observed when PBTDI chemically interacted with the soap network. However, the effectiveness of PBTDI as rheology modifier was much lower when the addition took place at earlier steps of the manufacturing process. Some competitive reactions due to either the presence of water or the high temperatures applied have been proposed to explain this loss of effectiveness depending on the Lubricating Grease processing stage at which PBTDI was added. ?? 2006 Elsevier B.V. All rights reserved.
J M Franco - One of the best experts on this subject based on the ideXlab platform.
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evaluation of different polyolefins as rheology modifier additives in Lubricating Grease formulations
Materials Chemistry and Physics, 2011Co-Authors: J E Martinalfonso, M C Sanchez, J M Franco, C Valencia, C GallegosAbstract:Abstract The purpose of the present work is to evaluate the effect that different polyolefins, used as additives in small proportions, exert on the rheological properties of standard lithium Lubricating Greases. Grease formulations containing several polyolefins, differing in nature and molecular weight, were manufactured and rheologically characterized. The influence of the type of polymer, molecular weight, crystallinity degree and vinyl acetate content has been analyzed. Small-amplitude oscillatory shear (SAOS) and viscous flow measurements, as well as calorimetric (DSC) and thermogravimetric (TGA) analysis, were carried out. In general, the addition of polymers such as HDPE, LDPE, LLDPE and PP to lithium Lubricating Greases significantly increases the values of the rheological parameters analyzed, consistency and mechanical stability. However, the use of polyolefins as rheology modifiers does not significantly affect the friction coefficient determined in a tribological contact. The crystallinity degree, mainly dependent on the nature of the polymer, has been found the most highly influencing parameter on the rheology of the Lubricating Greases studied. However, the rheological modification exerted by EVA copolymers mainly depends on the vinyl acetate content. Thus, a negative effect in both apparent viscosity and linear viscoelastic functions of Greases was obtained when polymer vinyl acetate content is higher than 28% (w/w).
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Evaluation of different polyolefins as rheology modifier additives in Lubricating Grease formulations
Materials Chemistry and Physics, 2011Co-Authors: J. E. MartÃn-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo GallegosAbstract:The purpose of the present work is to evaluate the effect that different polyolefins, used as additives in small proportions, exert on the rheological properties of standard lithium Lubricating Greases. Grease formulations containing several polyolefins, differing in nature and molecular weight, were manufactured and rheologically characterized. The influence of the type of polymer, molecular weight, crystallinity degree and vinyl acetate content has been analyzed. Small-amplitude oscillatory shear (SAOS) and viscous flow measurements, as well as calorimetric (DSC) and thermogravimetric (TGA) analysis, were carried out. In general, the addition of polymers such as HDPE, LDPE, LLDPE and PP to lithium Lubricating Greases significantly increases the values of the rheological parameters analyzed, consistency and mechanical stability. However, the use of polyolefins as rheology modifiers does not significantly affect the friction coefficient determined in a tribological contact. The crystallinity degree, mainly dependent on the nature of the polymer, has been found the most highly influencing parameter on the rheology of the Lubricating Greases studied. However, the rheological modification exerted by EVA copolymers mainly depends on the vinyl acetate content. Thus, a negative effect in both apparent viscosity and linear viscoelastic functions of Greases was obtained when polymer vinyl acetate content is higher than 28% (w/w). © 2011 Elsevier B.V. All rights reserved.
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Recycled and virgin LDPE as rheology modifiers of lithium Lubricating Greases: A comparative study
Polymer Engineering and Science, 2008Co-Authors: J.e. Martín-alfonso, Carlos Valencia, M C Sanchez, J M Franco, Crispulo GallegosAbstract:In this work, a new application for recycled low-density polyethylene (LDPE), as rheology modifier of standard lithium Lubricating Grease formulations, was studied. The effectiveness of this additive was compared with that achieved with a virgin LDPE. With this aim, both types of polymers were added to the formulation during the manufacturing process of Greases, following the same standard protocol, to reinforce the role of the thickening agent, the lithium 12-hidroxystearate. The effect that both lithium soap and LDPE concentrations exert on the rheology of Lubricating Grease formulations and its relationship with Grease microstructure were discussed. Lubricating Greases were rheologically characterized through small-amplitude oscillatory shear and viscous flow measurements. In addition to these, scanning electron microscopy observations and mechanical stability tests were also carried out. In all cases, an increase in soap concentration yields higher values of apparent viscosity and linear viscoelasticity functions. On the other hand, the values of the rheological functions obtained for recycled LDPE-based Lubricating Greases are, in general, higher than those obtained for virgin LDPE-based Grease formulations. However, the structural skeleton developed in Greases containing recycled LDPE demonstrates less resistance to severe working conditions, showing lower mechanical stability than virgin LDPE-based Grease formulations. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
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Rheology and microstructure of lithium Lubricating Greases modified with a reactive diisocyanate-terminated polymer: Influence of polymer addition protocol
Chemical Engineering and Processing: Process Intensification, 2008Co-Authors: G Moreno, M. V. de Paz, Carlos Valencia, J M Franco, Crispulo GallegosAbstract:This work deals with the influence that the addition of poly(1,4-butanediol) tolylene 2,4-diisocyanate terminated prepolymer (PBTDI) at different stages during the manufacturing process of a traditional lithium Lubricating Grease exerts on its rheological and morphological characteristics. With this aim, the reaction between terminal isocyanate groups and the hydroxy group located in the hydrocarbon chain of the 12-hydroxystearate lithium soap was intended to be promoted during Lubricating Grease processing. Several PBTDI-based Greases just differing in the process stage at which this polymer was added were prepared. The polymer used and the final Lubricating Greases were characterized by FTIR spectroscopy and DSC techniques. The effect of PBTDI addition at different processing stages was tested on final Greases by performing small-amplitude oscillatory shear (SAOS) measurements as well as atomic force microscopy (AFM) observations. Addition of PBTDI significantly increased the values of the linear viscoelasticity functions when it was added during the final cooling stage of the manufacturing process. It was demonstrated that this increment in relation to the values found for the additive-free Lubricating Grease was only observed when PBTDI chemically interacted with the soap network. However, the effectiveness of PBTDI as rheology modifier was much lower when the addition took place at earlier steps of the manufacturing process. Some competitive reactions due to either the presence of water or the high temperatures applied have been proposed to explain this loss of effectiveness depending on the Lubricating Grease processing stage at which PBTDI was added. ?? 2006 Elsevier B.V. All rights reserved.
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Development of new Lubricating Grease formulations using recycled LDPE as rheology modifier additive
European Polymer Journal, 2007Co-Authors: J. E. MartÃn-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo GallegosAbstract:The recovery of plastic waste but also its applicability in product development may be an incentive to industry, since the use of such plastics represents a cheaper source of raw material. The aim of the present paper is to study the feasibility of recycling polyolefins as additives to improve the rheological properties of lithium 12-hydroxystearate Lubricating Greases. The effects that both soap and recycled low-density polyethylene (LDPE) concentration exert on the rheology of lithium Lubricating Greases and its relationship with Grease microstructure are discussed in this work. In this way, different Lubricating Grease formulations were manufactured by modifying the concentration of lithium 12-hydroxystearate and content of recycled LDPE, according to a RSM statistical design. These Lubricating Greases were rheologically characterized through small-amplitude oscillatory shear (SAOS) and viscous flow measurements. In addition to these, scanning electronic microscopy (SEM) observations and mechanical stability tests were also carried out. Recycled LDPE was found to be an effective additive to modify Grease rheology, acting as filler in the soap entangled microstructure. The values of both apparent viscosity and viscoelastic functions in the linear viscoelastic region increase with soap and recycled polymer concentrations. However, the addition of recycled LDPE distort the microstructural network of these Greases resulting Greases with less relative elastic characteristics and poorer mechanical properties as LDPE content increases. ?? 2006 Elsevier Ltd. All rights reserved.
C Gallegos - One of the best experts on this subject based on the ideXlab platform.
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evaluation of different polyolefins as rheology modifier additives in Lubricating Grease formulations
Materials Chemistry and Physics, 2011Co-Authors: J E Martinalfonso, M C Sanchez, J M Franco, C Valencia, C GallegosAbstract:Abstract The purpose of the present work is to evaluate the effect that different polyolefins, used as additives in small proportions, exert on the rheological properties of standard lithium Lubricating Greases. Grease formulations containing several polyolefins, differing in nature and molecular weight, were manufactured and rheologically characterized. The influence of the type of polymer, molecular weight, crystallinity degree and vinyl acetate content has been analyzed. Small-amplitude oscillatory shear (SAOS) and viscous flow measurements, as well as calorimetric (DSC) and thermogravimetric (TGA) analysis, were carried out. In general, the addition of polymers such as HDPE, LDPE, LLDPE and PP to lithium Lubricating Greases significantly increases the values of the rheological parameters analyzed, consistency and mechanical stability. However, the use of polyolefins as rheology modifiers does not significantly affect the friction coefficient determined in a tribological contact. The crystallinity degree, mainly dependent on the nature of the polymer, has been found the most highly influencing parameter on the rheology of the Lubricating Greases studied. However, the rheological modification exerted by EVA copolymers mainly depends on the vinyl acetate content. Thus, a negative effect in both apparent viscosity and linear viscoelastic functions of Greases was obtained when polymer vinyl acetate content is higher than 28% (w/w).
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Rheology and microstructure of lithium Lubricating Greases modified with a reactive diisocyanate-terminated polymer: Influence of polymer addition protocol
Chemical Engineering and Processing, 2008Co-Authors: G Moreno, José M. Franco, Concepción Valencia, C GallegosAbstract:Abstract This work deals with the influence that the addition of poly(1,4-butanediol) tolylene 2,4-diisocyanate terminated prepolymer (PBTDI) at different stages during the manufacturing process of a traditional lithium Lubricating Grease exerts on its rheological and morphological characteristics. With this aim, the reaction between terminal isocyanate groups and the hydroxy group located in the hydrocarbon chain of the 12-hydroxystearate lithium soap was intended to be promoted during Lubricating Grease processing. Several PBTDI-based Greases just differing in the process stage at which this polymer was added were prepared. The polymer used and the final Lubricating Greases were characterized by FTIR spectroscopy and DSC techniques. The effect of PBTDI addition at different processing stages was tested on final Greases by performing small-amplitude oscillatory shear (SAOS) measurements as well as atomic force microscopy (AFM) observations. Addition of PBTDI significantly increased the values of the linear viscoelasticity functions when it was added during the final cooling stage of the manufacturing process. It was demonstrated that this increment in relation to the values found for the additive-free Lubricating Grease was only observed when PBTDI chemically interacted with the soap network. However, the effectiveness of PBTDI as rheology modifier was much lower when the addition took place at earlier steps of the manufacturing process. Some competitive reactions due to either the presence of water or the high temperatures applied have been proposed to explain this loss of effectiveness depending on the Lubricating Grease processing stage at which PBTDI was added.
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development of new Lubricating Grease formulations using recycled ldpe as rheology modifier additive
European Polymer Journal, 2007Co-Authors: J E Martinalfonso, M C Sanchez, J M Franco, C Valencia, C GallegosAbstract:The recovery of plastic waste but also its applicability in product development may be an incentive to industry, since the use of such plastics represents a cheaper source of raw material. The aim of the present paper is to study the feasibility of recycling polyolefins as additives to improve the rheological properties of lithium 12-hydroxystearate Lubricating Greases. The effects that both soap and recycled low-density polyethylene (LDPE) concentration exert on the rheology of lithium Lubricating Greases and its relationship with Grease microstructure are discussed in this work. In this way, different Lubricating Grease formulations were manufactured by modifying the concentration of lithium 12-hydroxystearate and content of recycled LDPE, according to a RSM statistical design. These Lubricating Greases were rheologically characterized through small-amplitude oscillatory shear (SAOS) and viscous flow measurements. In addition to these, scanning electronic microscopy (SEM) observations and mechanical stability tests were also carried out. Recycled LDPE was found to be an effective additive to modify Grease rheology, acting as filler in the soap entangled microstructure. The values of both apparent viscosity and viscoelastic functions in the linear viscoelastic region increase with soap and recycled polymer concentrations. However, the addition of recycled LDPE distort the microstructural network of these Greases resulting Greases with less relative elastic characteristics and poorer mechanical properties as LDPE content increases.
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thermorheological behaviour of a lithium Lubricating Grease
Tribology Letters, 2006Co-Authors: M A Delgado, M C Sanchez, J M Franco, C Valencia, C GallegosAbstract:Thermal-induced changes in the viscous and viscoelastic responses of Lubricating Greases have been investigated through different rheological techniques in a temperature range of 0–175 °C. Small-amplitude oscillatory shear and viscous flow measurements were carried out on a model conventional lithium Lubricating Grease prepared by inducing the in situ saponification reaction between 12-hydroxystearic acid and hydrated lithium hydroxide. The linear viscoelasticity functions dramatically decrease above 110 °C, but not below this critical temperature, which determines the maximum recommended operating temperature in relation to its durability and resistance under working conditions. Two different regions, below and above this critical temperature, in the plateau modulus versus temperature plot have been detected. From this thermal dependence, a much larger thermal susceptibility of the Lubricating Grease at temperatures above 110 °C is apparent. The thermo-mechanical reversibility of this material has been studied by applying different combined stress–temperature protocols. Regarding the viscous flow, a minimum in the shear stress versus shear rate plots appeared at temperatures above 60 °C, more pronounced as temperature increases, resulting from material instabilities. The experimental results obtained have been explained on the basis of the thermo-mechanical degradation of the Lubricating Grease microstructure.
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on the drag reduction for the two phase horizontal pipe flow of highly viscous non newtonian liquid air mixtures case of Lubricating Grease
International Journal of Multiphase Flow, 2006Co-Authors: M J Ruizviera, M A Delgado, M C Sanchez, J M Franco, C GallegosAbstract:Abstract The prediction of the pressure drop gradient and the evaluation of the drag reduction phenomenon observed during the piping multiphase flow of a Lubricating Grease/air mixture have been investigated. With this aim, viscous flow tests in rotational rheometers and pressure drop measurements in pipelines have been carried out using different geometries with both smooth and rough surfaces. The Sisko model has been used to predict the pressure drop gradient. The drag ratio, as a function of air flow rate, for highly viscous pastes such as Lubricating Greases, significantly differs, qualitative and quantitatively, from that found in the literature for other non-Newtonian fluids with viscosities of around 200 times lower. The pressure drop gradient in the intermittent multiphase flow regime can be predicted by modifying the classical approach of Lockhart and Martinelli with an empirical correction factor. An empirical model, with a combination of power-law and sigmoidal-type equations, has been proposed to describe the experimental evolution of the drag ratio as a function of Re L ′ / Re TP ′ . The accuracy of the proposed model has been tested by estimating the classical Fanning friction factor for a non-Newtonian fluid, f = 16/Re′, once the pressure loss has been corrected with the drag ratio previously obtained.
Carlos Valencia - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of different polyolefins as rheology modifier additives in Lubricating Grease formulations
Materials Chemistry and Physics, 2011Co-Authors: J. E. MartÃn-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo GallegosAbstract:The purpose of the present work is to evaluate the effect that different polyolefins, used as additives in small proportions, exert on the rheological properties of standard lithium Lubricating Greases. Grease formulations containing several polyolefins, differing in nature and molecular weight, were manufactured and rheologically characterized. The influence of the type of polymer, molecular weight, crystallinity degree and vinyl acetate content has been analyzed. Small-amplitude oscillatory shear (SAOS) and viscous flow measurements, as well as calorimetric (DSC) and thermogravimetric (TGA) analysis, were carried out. In general, the addition of polymers such as HDPE, LDPE, LLDPE and PP to lithium Lubricating Greases significantly increases the values of the rheological parameters analyzed, consistency and mechanical stability. However, the use of polyolefins as rheology modifiers does not significantly affect the friction coefficient determined in a tribological contact. The crystallinity degree, mainly dependent on the nature of the polymer, has been found the most highly influencing parameter on the rheology of the Lubricating Greases studied. However, the rheological modification exerted by EVA copolymers mainly depends on the vinyl acetate content. Thus, a negative effect in both apparent viscosity and linear viscoelastic functions of Greases was obtained when polymer vinyl acetate content is higher than 28% (w/w). © 2011 Elsevier B.V. All rights reserved.
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Recycled and virgin LDPE as rheology modifiers of lithium Lubricating Greases: A comparative study
Polymer Engineering and Science, 2008Co-Authors: J.e. Martín-alfonso, Carlos Valencia, M C Sanchez, J M Franco, Crispulo GallegosAbstract:In this work, a new application for recycled low-density polyethylene (LDPE), as rheology modifier of standard lithium Lubricating Grease formulations, was studied. The effectiveness of this additive was compared with that achieved with a virgin LDPE. With this aim, both types of polymers were added to the formulation during the manufacturing process of Greases, following the same standard protocol, to reinforce the role of the thickening agent, the lithium 12-hidroxystearate. The effect that both lithium soap and LDPE concentrations exert on the rheology of Lubricating Grease formulations and its relationship with Grease microstructure were discussed. Lubricating Greases were rheologically characterized through small-amplitude oscillatory shear and viscous flow measurements. In addition to these, scanning electron microscopy observations and mechanical stability tests were also carried out. In all cases, an increase in soap concentration yields higher values of apparent viscosity and linear viscoelasticity functions. On the other hand, the values of the rheological functions obtained for recycled LDPE-based Lubricating Greases are, in general, higher than those obtained for virgin LDPE-based Grease formulations. However, the structural skeleton developed in Greases containing recycled LDPE demonstrates less resistance to severe working conditions, showing lower mechanical stability than virgin LDPE-based Grease formulations. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
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Rheology and microstructure of lithium Lubricating Greases modified with a reactive diisocyanate-terminated polymer: Influence of polymer addition protocol
Chemical Engineering and Processing: Process Intensification, 2008Co-Authors: G Moreno, M. V. de Paz, Carlos Valencia, J M Franco, Crispulo GallegosAbstract:This work deals with the influence that the addition of poly(1,4-butanediol) tolylene 2,4-diisocyanate terminated prepolymer (PBTDI) at different stages during the manufacturing process of a traditional lithium Lubricating Grease exerts on its rheological and morphological characteristics. With this aim, the reaction between terminal isocyanate groups and the hydroxy group located in the hydrocarbon chain of the 12-hydroxystearate lithium soap was intended to be promoted during Lubricating Grease processing. Several PBTDI-based Greases just differing in the process stage at which this polymer was added were prepared. The polymer used and the final Lubricating Greases were characterized by FTIR spectroscopy and DSC techniques. The effect of PBTDI addition at different processing stages was tested on final Greases by performing small-amplitude oscillatory shear (SAOS) measurements as well as atomic force microscopy (AFM) observations. Addition of PBTDI significantly increased the values of the linear viscoelasticity functions when it was added during the final cooling stage of the manufacturing process. It was demonstrated that this increment in relation to the values found for the additive-free Lubricating Grease was only observed when PBTDI chemically interacted with the soap network. However, the effectiveness of PBTDI as rheology modifier was much lower when the addition took place at earlier steps of the manufacturing process. Some competitive reactions due to either the presence of water or the high temperatures applied have been proposed to explain this loss of effectiveness depending on the Lubricating Grease processing stage at which PBTDI was added. ?? 2006 Elsevier B.V. All rights reserved.
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Development of new Lubricating Grease formulations using recycled LDPE as rheology modifier additive
European Polymer Journal, 2007Co-Authors: J. E. MartÃn-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo GallegosAbstract:The recovery of plastic waste but also its applicability in product development may be an incentive to industry, since the use of such plastics represents a cheaper source of raw material. The aim of the present paper is to study the feasibility of recycling polyolefins as additives to improve the rheological properties of lithium 12-hydroxystearate Lubricating Greases. The effects that both soap and recycled low-density polyethylene (LDPE) concentration exert on the rheology of lithium Lubricating Greases and its relationship with Grease microstructure are discussed in this work. In this way, different Lubricating Grease formulations were manufactured by modifying the concentration of lithium 12-hydroxystearate and content of recycled LDPE, according to a RSM statistical design. These Lubricating Greases were rheologically characterized through small-amplitude oscillatory shear (SAOS) and viscous flow measurements. In addition to these, scanning electronic microscopy (SEM) observations and mechanical stability tests were also carried out. Recycled LDPE was found to be an effective additive to modify Grease rheology, acting as filler in the soap entangled microstructure. The values of both apparent viscosity and viscoelastic functions in the linear viscoelastic region increase with soap and recycled polymer concentrations. However, the addition of recycled LDPE distort the microstructural network of these Greases resulting Greases with less relative elastic characteristics and poorer mechanical properties as LDPE content increases. ?? 2006 Elsevier Ltd. All rights reserved.
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Influence of soap concentration and oil viscosity on the rheology and microstructure of Lubricating Greases
Industrial and Engineering Chemistry Research, 2006Co-Authors: M A Delgado, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo GallegosAbstract:The effects that both soap concentration and base oil viscosity exert on the rheology of Lubricating Greases and its relationship with Grease microstructure are discussed in this work. With this aim, different Lubricating Grease formulations were manufactured by modifying the concentration of lithium 12-hydroxystearate and the viscosity of the base oil, according to an RSM statistical design. These Lubricating Greases were rheologically characterized through small-amplitude oscillatory shear (SAOS) and viscous flow measurements. In addition to these, scanning electronic microscopy (SEM) observations and mechanical stability tests were also carried out. It has been found that the structural skeleton (size and shape of the disperse phase particles) was highly influenced by the base oil viscosity. In this sense, the values of the viscoelastic functions in the linear viscoelastic region and the mechanical stability of the Lubricating Greases increase as the viscosity of the base oil decreases. An opposite tendency was observed during viscous flow tests at high shear rates, when the Grease microstructure was mostly destroyed. On the other hand, the microstructural network of these Greases becomes stronger as soap concentration increases. These results have been explained taking into account the balance between the solvency of the thickener in the base oil and the level of entanglements formed by soap fibers, which influence the Lubricating Grease network.
M. C. Sánchez - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of different polyolefins as rheology modifier additives in Lubricating Grease formulations
Materials Chemistry and Physics, 2011Co-Authors: J. E. MartÃn-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo GallegosAbstract:The purpose of the present work is to evaluate the effect that different polyolefins, used as additives in small proportions, exert on the rheological properties of standard lithium Lubricating Greases. Grease formulations containing several polyolefins, differing in nature and molecular weight, were manufactured and rheologically characterized. The influence of the type of polymer, molecular weight, crystallinity degree and vinyl acetate content has been analyzed. Small-amplitude oscillatory shear (SAOS) and viscous flow measurements, as well as calorimetric (DSC) and thermogravimetric (TGA) analysis, were carried out. In general, the addition of polymers such as HDPE, LDPE, LLDPE and PP to lithium Lubricating Greases significantly increases the values of the rheological parameters analyzed, consistency and mechanical stability. However, the use of polyolefins as rheology modifiers does not significantly affect the friction coefficient determined in a tribological contact. The crystallinity degree, mainly dependent on the nature of the polymer, has been found the most highly influencing parameter on the rheology of the Lubricating Greases studied. However, the rheological modification exerted by EVA copolymers mainly depends on the vinyl acetate content. Thus, a negative effect in both apparent viscosity and linear viscoelastic functions of Greases was obtained when polymer vinyl acetate content is higher than 28% (w/w). © 2011 Elsevier B.V. All rights reserved.
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Development of new Lubricating Grease formulations using recycled LDPE as rheology modifier additive
European Polymer Journal, 2007Co-Authors: J. E. MartÃn-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo GallegosAbstract:The recovery of plastic waste but also its applicability in product development may be an incentive to industry, since the use of such plastics represents a cheaper source of raw material. The aim of the present paper is to study the feasibility of recycling polyolefins as additives to improve the rheological properties of lithium 12-hydroxystearate Lubricating Greases. The effects that both soap and recycled low-density polyethylene (LDPE) concentration exert on the rheology of lithium Lubricating Greases and its relationship with Grease microstructure are discussed in this work. In this way, different Lubricating Grease formulations were manufactured by modifying the concentration of lithium 12-hydroxystearate and content of recycled LDPE, according to a RSM statistical design. These Lubricating Greases were rheologically characterized through small-amplitude oscillatory shear (SAOS) and viscous flow measurements. In addition to these, scanning electronic microscopy (SEM) observations and mechanical stability tests were also carried out. Recycled LDPE was found to be an effective additive to modify Grease rheology, acting as filler in the soap entangled microstructure. The values of both apparent viscosity and viscoelastic functions in the linear viscoelastic region increase with soap and recycled polymer concentrations. However, the addition of recycled LDPE distort the microstructural network of these Greases resulting Greases with less relative elastic characteristics and poorer mechanical properties as LDPE content increases. ?? 2006 Elsevier Ltd. All rights reserved.
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Influence of soap concentration and oil viscosity on the rheology and microstructure of Lubricating Greases
Industrial and Engineering Chemistry Research, 2006Co-Authors: M A Delgado, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo GallegosAbstract:The effects that both soap concentration and base oil viscosity exert on the rheology of Lubricating Greases and its relationship with Grease microstructure are discussed in this work. With this aim, different Lubricating Grease formulations were manufactured by modifying the concentration of lithium 12-hydroxystearate and the viscosity of the base oil, according to an RSM statistical design. These Lubricating Greases were rheologically characterized through small-amplitude oscillatory shear (SAOS) and viscous flow measurements. In addition to these, scanning electronic microscopy (SEM) observations and mechanical stability tests were also carried out. It has been found that the structural skeleton (size and shape of the disperse phase particles) was highly influenced by the base oil viscosity. In this sense, the values of the viscoelastic functions in the linear viscoelastic region and the mechanical stability of the Lubricating Greases increase as the viscosity of the base oil decreases. An opposite tendency was observed during viscous flow tests at high shear rates, when the Grease microstructure was mostly destroyed. On the other hand, the microstructural network of these Greases becomes stronger as soap concentration increases. These results have been explained taking into account the balance between the solvency of the thickener in the base oil and the level of entanglements formed by soap fibers, which influence the Lubricating Grease network.
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Relationship Among Microstructure, Rheology and Processing of a Lithium Lubricating Grease
Chemical Engineering Research and Design, 2005Co-Authors: M A Delgado, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo GallegosAbstract:The overall objective of this work was to evaluate the evolution of the microstructure and rheology of a Lubricating Grease during its manufacturing process. With this aim, lithium Lubricating Greases were prepared by inducing the saponification reaction between 12-hydroxystearic acid and hydrated lithium hydroxide within a naphtenic Lubricating oil medium, applying a controlled-temperature programme. The manufacturing process was followed through the mixing rheometry technique by measuring the evolution of torque with processing time. Samples of incipient and finished Grease were taken from the stirred tank at different processing times. Rheological (linear viscoelasticity and viscous flow) and mechanical stability tests, as well as morphological studies, were carried out on each sample. The changes found in the microstructure and rheology of a Lubricating Grease during its processing have been related to the soap concentration in the reacting mixture, the waxy soap transition at high temperatures and the further cooling steps. From the experimental results obtained, we may conclude that a suitable lithium Lubricating Grease is a highly structured system, based on the development of a three-dimensional network due to the presence of metallic soap crystallites.
