The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform

Crispulo Gallegos - One of the best experts on this subject based on the ideXlab platform.

  • Evaluation of different polyolefins as Rheology Modifier additives in lubricating grease formulations
    Materials Chemistry and Physics, 2011
    Co-Authors: J. E. Martín-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo Gallegos
    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). © 2011 Elsevier B.V. All rights reserved.

  • Recycled and virgin LDPE as Rheology Modifiers of lithium lubricating greases: A comparative study
    Polymer Engineering and Science, 2008
    Co-Authors: J.e. Martín-alfonso, Carlos Valencia, M C Sanchez, J M Franco, Crispulo Gallegos
    Abstract:

    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

  • 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, 2008
    Co-Authors: G Moreno, M. V. de Paz, Carlos Valencia, J M Franco, Crispulo Gallegos
    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. ?? 2006 Elsevier B.V. All rights reserved.

  • Development of new lubricating grease formulations using recycled LDPE as Rheology Modifier additive
    European Polymer Journal, 2007
    Co-Authors: J. E. Martín-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo Gallegos
    Abstract:

    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.

  • Use of reactive diisocyanate-terminated polymers as Rheology Modifiers of lubricating greases
    Industrial & Engineering Chemistry Research, 2006
    Co-Authors: G Moreno, J M Franco, Concepción Valencia, Crispulo Gallegos
    Abstract:

    In this work, the use of reactive diisocyanate-terminated polymeric materials as Rheology Modifiers of lubricating greases has been studied. 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 promoted during the processing of lubricating greases. The polymeric materials used and the final lubricating greases were characterized through 'H NMR, IR, differential scanning calorimetry (DSC), and gel permeation chromatography (GPC) techniques. The effectiveness of such additives was tested on final greases by performing small-amplitude oscillatory shear (SAOS) and viscous flow measurements as well as standardized mechanical stability tests. The rheological response was also related to the microstructure of these greases. From the experimental results obtained, it may be concluded that a reactive diisocyanate-terminated polymer with relatively low molecular weight (M n = 1800), such as poly(l,4-butanediol)tolylene 2,4-diisocyanate (PBTDI), can be satisfactorily used as a Rheology Modifier in grease formulations. Their effectiveness is similar to that achieved with nonreactive polymers of much higher molecular weight, such as low-density polyethylene (LDPE), also showing better mechanical stability than polyethylene-based greases. On the other hand, a triblock copolymer PBTDI-PEO-PBTDI was synthesized in order to increase the molecular weight of the diisocyanate-terminated polymeric additive. However, lower increments in the linear viscoelastic functions were found for greases containing PBTDI-PEO-PBTDI copolymer as additive, a fact that has been explained on the basis of its lower reactive isocyanate groups/molecular weight ratio and the presence of other macromolecules without terminal isocyanate groups.

J M Franco - One of the best experts on this subject based on the ideXlab platform.

  • evaluation of different polyolefins as Rheology Modifier additives in lubricating grease formulations
    Materials Chemistry and Physics, 2011
    Co-Authors: J E Martinalfonso, M C Sanchez, J M Franco, C Valencia, C Gallegos
    Abstract:

    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).

  • Evaluation of different polyolefins as Rheology Modifier additives in lubricating grease formulations
    Materials Chemistry and Physics, 2011
    Co-Authors: J. E. Martín-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo Gallegos
    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). © 2011 Elsevier B.V. All rights reserved.

  • Recycled and virgin LDPE as Rheology Modifiers of lithium lubricating greases: A comparative study
    Polymer Engineering and Science, 2008
    Co-Authors: J.e. Martín-alfonso, Carlos Valencia, M C Sanchez, J M Franco, Crispulo Gallegos
    Abstract:

    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

  • 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, 2008
    Co-Authors: G Moreno, M. V. de Paz, Carlos Valencia, J M Franco, Crispulo Gallegos
    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. ?? 2006 Elsevier B.V. All rights reserved.

  • Development of new lubricating grease formulations using recycled LDPE as Rheology Modifier additive
    European Polymer Journal, 2007
    Co-Authors: J. E. Martín-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo Gallegos
    Abstract:

    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.

Carlos Valencia - One of the best experts on this subject based on the ideXlab platform.

  • Evaluation of different polyolefins as Rheology Modifier additives in lubricating grease formulations
    Materials Chemistry and Physics, 2011
    Co-Authors: J. E. Martín-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo Gallegos
    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). © 2011 Elsevier B.V. All rights reserved.

  • Recycled and virgin LDPE as Rheology Modifiers of lithium lubricating greases: A comparative study
    Polymer Engineering and Science, 2008
    Co-Authors: J.e. Martín-alfonso, Carlos Valencia, M C Sanchez, J M Franco, Crispulo Gallegos
    Abstract:

    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

  • 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, 2008
    Co-Authors: G Moreno, M. V. de Paz, Carlos Valencia, J M Franco, Crispulo Gallegos
    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. ?? 2006 Elsevier B.V. All rights reserved.

  • Development of new lubricating grease formulations using recycled LDPE as Rheology Modifier additive
    European Polymer Journal, 2007
    Co-Authors: J. E. Martín-Alfonso, M. C. Sánchez, Carlos Valencia, J M Franco, Crispulo Gallegos
    Abstract:

    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.

  • evaluation of different polyolefins as Rheology Modifier additives in lubricating grease formulations
    Materials Chemistry and Physics, 2011
    Co-Authors: J E Martinalfonso, M C Sanchez, J M Franco, C Valencia, C Gallegos
    Abstract:

    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).

  • development of new lubricating grease formulations using recycled ldpe as Rheology Modifier additive
    European Polymer Journal, 2007
    Co-Authors: J E Martinalfonso, M C Sanchez, J M Franco, C Valencia, C Gallegos
    Abstract:

    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.

J E Martinalfonso - One of the best experts on this subject based on the ideXlab platform.

  • evaluation of different polyolefins as Rheology Modifier additives in lubricating grease formulations
    Materials Chemistry and Physics, 2011
    Co-Authors: J E Martinalfonso, M C Sanchez, J M Franco, C Valencia, C Gallegos
    Abstract:

    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).

  • development of new lubricating grease formulations using recycled ldpe as Rheology Modifier additive
    European Polymer Journal, 2007
    Co-Authors: J E Martinalfonso, M C Sanchez, J M Franco, C Valencia, C Gallegos
    Abstract:

    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.