The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform
Pieter Martin Lugt - One of the best experts on this subject based on the ideXlab platform.
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The Influence of Base Oil Properties on the Friction Behaviour of Lithium Greases in Rolling/Sliding Concentrated Contacts
Tribology Letters, 2017Co-Authors: Nicolino De Laurentis, Philippa Cann, Pieter Martin Lugt, ALEN KADIRICAbstract:This study investigates the influence of base oil type and viscosity on the frictional behaviour of lithium-thickened bearing Greases. A series of model lithium Greases were manufactured by systematically varying viscosity and type of base oil, so that the influence of a single base oil property could be studied in isolation. In addition, selected Greases were blended with oleic acid, with the purpose of evaluating its effectiveness in further reducing Grease friction. Friction coefficient and film thickness were measured in laboratory ball-on-disc tribometers over a range of speeds and temperatures. For a specific oil type, the influence of base oil viscosity on friction was found to be closely related to its effect on film thickness: Greases formulated with PAO oils covering a wide range of viscosities gave very similar friction at the same nominal film thickness. For a given base oil viscosity, base oil type was found to have a strong influence on Grease friction under all test conditions. PAO-based Greases generally produced lower friction than mineral- and ester-based Greases. Addition of oleic acid to the test Greases did not significantly affect friction within the range of test conditions employed in this study. The results provide new insight into the frictional behaviour of Greases, which may be used to help inform new low-friction Grease formulations for rolling bearing applications.
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Yield Stress and Low-Temperature Start-Up Torque of Lubricating Greases
Tribology Letters, 2016Co-Authors: F. Cyriac, Pieter Martin Lugt, R. BosmanAbstract:A comprehensive study of the yield stress and start-up torque for six commonly used rolling bearing Greases is presented. Both parameters were found to depend exponentially on temperature where the exponent changes below a low-temperature “break point.” This break point was found to be related to the pourpoint of the base oil, although the start-up torques of the Greases were an order higher in magnitude than that of their corresponding bled oils. The start-up torque is mostly used to measure the low-temperature limit of a Grease. It was found here that this temperature is much lower than the break point. The start-up torque criterion is measured using a particular bearing type and conditions. The low-temperature break point for the yield stress is a more universal Grease parameter that gives useful information about the behavior of a Grease at low temperatures and can be used as one of the guidelines for Grease selection for low-temperature applications.
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Impact of Water on EHL Film Thickness of Lubricating Greases in Rolling Point Contacts
Tribology Letters, 2016Co-Authors: F. Cyriac, Pieter Martin Lugt, R. Bosman, C. H. VennerAbstract:This paper investigates the influence of water on the EHL film thickness of six commercial lubricating Greases under fully flooded and starved conditions. Although Grease can absorb large quantities of water, separation occurs due to pressure and shear, leading to free water. This does not have an impact on the film thickness under fully flooded conditions. However, water does have an effect on the film thickness under starved conditions where the differences are related to the change in oil bleed. In the presence of water, an increase in oil bleed was found for lithium, lithium complex and polyurea Grease. These Greases showed a reduction in the levels of starvation and, therefore, thicker films. Water contamination led to lower oil bleed for calcium sulfonate complex Greases, which led to an increase in starvation, and therefore, thinner films compared to their uncontaminated counterparts.
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the influence of bearing Grease composition on friction in rolling sliding concentrated contacts
Tribology International, 2016Co-Authors: Nicolino De Laurentis, Pieter Martin Lugt, ALEN KADIRIC, Philippa CannAbstract:This paper presents new results examining the relationship between bearing Grease composition and rolling-sliding friction in lubricated contacts. Friction coefficient and lubricating film thickness of a series of commercially available bearing Greases and their bled oils were measured in laboratory tribometers. Test Greases were selected to cover a wide spectrum of thickener and base oil types, and base oil viscosities. The trends in measured friction coefficients were analysed in relation to Grease composition in an attempt to establish the relative influence of individual Grease components on friction. Two distinct operating regions with markedly different friction behaviour are identified for each Grease. At relatively high speeds the Greases behave approximately as their bled/base oils, while in the low speed region the frictional response is very dependent on their thickener type and properties of the lubricating film. Low viscosity, synthetic base oil seems to offer efficiency advantages in the high speed region regardless of thickener used, while the choice of thickener type is significant under low speed conditions.
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Impact of Water on the Rheology of Lubricating Greases
Tribology Transactions, 2016Co-Authors: F. Cyriac, Pieter Martin Lugt, Remi BosmanAbstract:ABSTRACTThe operational life of bearings is often determined by the performance of the lubricating Grease. The consistency of the Grease prevents it from leaking out of the bearing and provides good sealing properties. The possible ingress of water into the bearing will have a considerable impact not only on this consistency but also on the lubricating ability of the Grease. There are numerous applications where water ingress may occur, such as in the steel, food, pulp, and paper industries. Some Greases are less sensitive to water than others. No specific guidelines are available to select the proper Grease for bearings subjected to water ingress. The goal of the article is to contribute to the development of such guidelines for Greases subjected to water ingress by studying the impact of water on Grease rheology. Fully formulated, commercially available Greases with the most common thickeners and base oils are used as model Greases. It will be shown that water strongly influences rheological properties such as zero-shear viscosity, yield stress, and storage modulus. Calcium sulfonate Greases were found to become stiffer after absorbing a considerable amount of water, leading to an increase in zero-shear viscosity and yield stress. However, lithium, lithium complex, and polyurea Greases were found to soften, with appreciable changes in measured rheological properties.
Críspulo Gallegos - One of the best experts on this subject based on the ideXlab platform.
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Influence of soap/polymer concentration ratio on the rheological properties of lithium lubricating Greases modified with virgin LDPE
Journal of Industrial and Engineering Chemistry, 2009Co-Authors: J. E. MartÃn-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, G Moreno, Críspulo GallegosAbstract:The main goal of this work was to study the feasibility of using a low-density polyethylene (LDPE) as additive to improve the rheological properties of lithium lubricating Greases. The combined effect that both soap and LDPE concentrations exerts on the rheology of lithium lubricating Greases and its relationship with Grease microstructure were studied according to an experimental design based on the response surface methodology (RSM). Different lubricating Grease formulations were manufactured by modifying lithium 12-hydroxystereate and LDPE concentrations. Small-amplitude oscillatory shear (SAOS) and viscous flow measurements, as well as mechanical stability tests, were performed. In addition to these, environmental scanning electronic microscopy (ESEM) was used to determine Grease microstructure. LDPE was found to be a useful additive to modify Grease rheology, acting as filler in the entangled soap network. The values of both apparent viscosity and linear viscoelasticity functions increase with soap and LDPE concentration. However, the addition of LDPE distorts soap microstructural network, yielding Greases with lower relative elastic characteristics. © 2009 The Korean Society of Industrial and Engineering Chemistry.
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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, Críspulo 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, Críspulo 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, Críspulo 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, Críspulo 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.
Jorge H.o. Seabra - One of the best experts on this subject based on the ideXlab platform.
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Formulation, rheology and thermal ageing of polymer Greases - Part I: Influence of the thickener content
Tribology International, 2015Co-Authors: David Gon??alves, Armando V. Campos, Beatriz Graça, Jorge H.o. Seabra, René WestbroekAbstract:The aim of this work is to show the correlation between polymer Greases' rheology and its formulation. The tested polypropylene (PP) thickened Greases were evaluated regarding their thickener content and its effect on the rheological properties. An artificial ageing procedure was performed by heating fresh Grease samples in an oven to study the thermal degradation. The ageing evaluation was performed through rheological measurements, FT-IR spectra, oil loss, bleed-oil viscosity changes and bleed rate. The rheology measurements were performed on a rotational rheometer, emphasizing on the storage and loss moduli values at the Linear Visco-Elastic (LVE) region. The flow curve of each Grease was also measured. A modified Herschel-Buckley model was applied and the data was correlated to the thickener content.
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Influence of Grease rheology on thrust ball bearings friction torque
Tribology International, 2012Co-Authors: Tiago Cousseau, Beatriz M. Graça, Armando V. Campos, Jorge H.o. SeabraAbstract:The friction torque and the operating temperatures in a thrust ball bearing were measured for seven different types of Greases, including three biodegradable Greases having low toxicity. These friction torque tests were performed using a modified Four-Ball machine. Rheological evaluations of the lubricating Greases were made using a rheometer. Bleed oils were extracted from the Greases and the dynamic viscosities were measured. In order to compare the performance of the lubricant Greases in terms of friction, the Grease characteristics were related to experimental results, showing that the interaction between thickener and base oil have strong influences in the bearing friction torque. © 2011 Elsevier Ltd.
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Friction and wear in thrust ball bearings lubricated with biodegradable Greases
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2011Co-Authors: Tiago Cousseau, Beatriz M. Graça, Armando V. Campos, Jorge H.o. SeabraAbstract:Thrust ball bearings lubricated with several different types of Grease, including three biodegradable low-toxicity Greases, were tested in a modified four-ball machine in order to evaluate the bearing friction torque. At the end of each test, Grease samples were obtained and analysed through ferrography, allowing the quantification and evaluation of the bearing wear. In order to compare the Grease performance in terms of friction and wear, a correlation between the Grease characteristics (base oil, bleed oil, thickener structure, and rheological parameters) and the experimental results was established.
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Influence of Grease formulation on thrust bearings power loss
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 2010Co-Authors: Tiago Cousseau, Armando V. Campos, Beatriz Graça, Jorge H.o. SeabraAbstract:The minimization of the power loss and the use of the biodegradable Greases have attracting considerable attention. To compare the energetic performance of biodegradable lubricant Greases, power loss tests were performed on a modified four-ball machine. A correlation between the Grease formulation and rheology was established with its energetic performance.
Carlos Valencia - One of the best experts on this subject based on the ideXlab platform.
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Influence of soap/polymer concentration ratio on the rheological properties of lithium lubricating Greases modified with virgin LDPE
Journal of Industrial and Engineering Chemistry, 2009Co-Authors: J. E. MartÃn-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, G Moreno, Críspulo GallegosAbstract:The main goal of this work was to study the feasibility of using a low-density polyethylene (LDPE) as additive to improve the rheological properties of lithium lubricating Greases. The combined effect that both soap and LDPE concentrations exerts on the rheology of lithium lubricating Greases and its relationship with Grease microstructure were studied according to an experimental design based on the response surface methodology (RSM). Different lubricating Grease formulations were manufactured by modifying lithium 12-hydroxystereate and LDPE concentrations. Small-amplitude oscillatory shear (SAOS) and viscous flow measurements, as well as mechanical stability tests, were performed. In addition to these, environmental scanning electronic microscopy (ESEM) was used to determine Grease microstructure. LDPE was found to be a useful additive to modify Grease rheology, acting as filler in the entangled soap network. The values of both apparent viscosity and linear viscoelasticity functions increase with soap and LDPE concentration. However, the addition of LDPE distorts soap microstructural network, yielding Greases with lower relative elastic characteristics. © 2009 The Korean Society of Industrial and Engineering Chemistry.
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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, Críspulo 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, Críspulo 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, Críspulo 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, Críspulo 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.
J M Franco - One of the best experts on this subject based on the ideXlab platform.
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Influence of soap/polymer concentration ratio on the rheological properties of lithium lubricating Greases modified with virgin LDPE
Journal of Industrial and Engineering Chemistry, 2009Co-Authors: J. E. MartÃn-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, G Moreno, Críspulo GallegosAbstract:The main goal of this work was to study the feasibility of using a low-density polyethylene (LDPE) as additive to improve the rheological properties of lithium lubricating Greases. The combined effect that both soap and LDPE concentrations exerts on the rheology of lithium lubricating Greases and its relationship with Grease microstructure were studied according to an experimental design based on the response surface methodology (RSM). Different lubricating Grease formulations were manufactured by modifying lithium 12-hydroxystereate and LDPE concentrations. Small-amplitude oscillatory shear (SAOS) and viscous flow measurements, as well as mechanical stability tests, were performed. In addition to these, environmental scanning electronic microscopy (ESEM) was used to determine Grease microstructure. LDPE was found to be a useful additive to modify Grease rheology, acting as filler in the entangled soap network. The values of both apparent viscosity and linear viscoelasticity functions increase with soap and LDPE concentration. However, the addition of LDPE distorts soap microstructural network, yielding Greases with lower relative elastic characteristics. © 2009 The Korean Society of Industrial and Engineering Chemistry.
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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, Críspulo 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, Críspulo 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, Críspulo 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, Críspulo 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.
