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This study reports on a novel strategy for manufacturing thickened gel-like castor oil formulations by dispersing electrospun lignin/ethylcellulose nanostructures. These thickened formulations were rheologically and tribologically evaluated with the aim of being proposed as alternative ecofriendly lubricating greases. Low-sulfonate kraft lignin (LSL) and ethylcellulose (EC) were dissolved in a DMAc:THF mixture at different concentrations (8, 10, and 15 wt.%) and LSL:EC ratios (50:50, 70:30, and 90:10) and subjected to electrospinning. The resulting electrospun nanostructures were morphologically characterized. EC acting as the cospinning polymer improved both LSL spinnability and the oil structuring ability. Solutions with a high lignin content achieved microsized particles connected by fibrils, whereas solutions with a high EC content (50:50 ratio) and LSL/EC total concentration (10 and 15 wt.%) yielded beaded or bead-free nanofibers, due to enhanced extensional viscoelastic properties and nonNewtonian characteristics. The gel-like properties of electrospun nanostructure dispersions in castor oil were strengthened with the nanostructure concentration and the EC:LSL ratio, as a result of the formation of a more interconnected fiber network. The oleodispersions studied exhibited a satisfactory frictional response in a tribological contact, with friction coefficient values that were comparable to those achieved with traditional lithium-lubricating greases, This work was supported by MCIN/AEI/10.13039/501100011033, by “ERDF—A way of making Europe” (grant number: RTI2018-096080-BC21) and by Junta de Andalucía/EPIT2020-UHU (grant numbers: PY20_00751 and UHU202029) by the FEDER European Programme

In this work we developed electrospun lignin/cellulose acetate fiber-bead nanostructures and explored their potential as structuring agents for vegetable oils to be used as eco-friendly lubricating oleogels. A variety of nanostructures were obtained from solutions containing 20 or 30 wt. % eucalyptus Kraft lignin (EKL) and cellulose acetate (CA) in variable weight ratios from 100:0 to 60:40 in an N,N-dimethylformamide/acetone mixture. The EKL/CA solutions were characterized in physicochemical terms from viscosity, surface tension and electrical conductivity measurements. Also, the electrospun nanostructures were characterized morphologically by scanning electron microscopy. Their morphology was found to be strongly dependent on the rheological properties of the biopolymer solution. Electrospun EKL/CA beaded nanofibers and well-developed uniform nanofiber mats allowed oleogels to be easily obtained by simply dispersing them in castor oil whilst nanoparticle clusters gave rise to unstable dispersions. The rheological properties of these gel-like dispersions can be tailored through the membrane concentration and/or EKL/CA ratio and depend to a large extent on the morphology of the electrospun nanostructures. The rheological and tribological properties of the oleogels were comparable to those previously reported for conventional and other bio-based lubricating greases. Overall, electrospun EKL/CA nanofibers allow easy, efficient structuring of vegetable oils to obtain oleogels holding potential for use as lubricants., Research Project RTI2018–096080-B-C21, funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”. PhD Research Grant PRE2019–090632 from Spain’s Ministry of Science and Innovation. Funding for open access charge: Universidad de Huelva / CBUA

Non-aqueous phase change emulsions are very unknown and promising multifunctional fluids consisting of phase change materials dispersed in carrier fluids, both being oily phases. The oil-in-oil phase change emulsions allow the possibility of using the same medium for latent heat storage and transport under more extreme pressure and temperature conditions. In this paper, stable emulsions composed of stearic acid with a melting point of 68–71 °C dispersed in silicone oil have been developed. Stearic acid-in-silicone oil emulsion samples with different phase concentrations were evaluated by analysing their thermophysical properties, viscous and viscoelastic behaviour and microstructure. Emulsion properties below the melting point of the phase change material were greatly influenced by the concentration of the disperse phase. Thus, as the temperature lowered, a well-developed three-dimensional network of stearic acid crystalline structures interconnected with each other was formed. Furthermore, emulsion physicochemical and thermal stabilities were examined and proved under several mechanical–thermal cycles, withstanding more than 100 cycles in the calorimeter. The results indicate that stearic acid-in-silicone oil emulsions are an attractive candidate for energy storage applications with a phase change enthalpy in emulsions with the 10 wt% of phase change material of 22.32 J/g., Non-aqueous phase change emulsions are very unknown and promising multifunctional fluids consisting of phase change materials dispersed in carrier fluids, both being oily phases. The oil-in-oil phase change emulsions allow the possibility of using the same medium for latent heat storage and transport under more extreme pressure and temperature conditions. In this paper, stable emulsions composed of stearic acid with a melting point of 68–71 C dispersed in silicone oil have been developed. Stearic acid-in-silicone oil emulsion samples with different phase concentrations were evaluated by analysing their thermophysical properties, viscous and viscoelastic behaviour and microstructure. Emulsion properties below the melting point of the phase change material were greatly influenced by the concentration of the disperse phase. Thus, as the temperature lowered, a well-developed three- dimensional network of stearic acid crystalline structures interconnected with each other was formed. Furthermore, emulsion physicochemical and thermal stabilities were examined and proved under several mechanical–thermal cycles, withstanding more than 100 cycles in the calorimeter. The results indicate that stearic acid-in-silicone oil emulsions are an attractive candidate for energy storage applications with a phase change enthalpy in emulsions with the 10 wt% of phase change material of 22.32 J/g.

Nowadays, the reduction of the environmental impact associated with the operation of the oil industry is a primary concern. A growing trend is to develop low-toxicity formulations based on biodegradable components. In this sense, vegetable oils structured with nanomaterials could be an alternative to mineral or synthetic oils for sustainable fluid formulations. Hydrophobic fumed silica nanoparticles have the capability to change the rheological behavior of oil in suspensions, providing a large variety of non-Newtonian behaviors over a wide range of temperatures, from shear-thinning to gel-like, depending on the concentration and the nanosilica’s hydrophobicity, that permits the design of fluids with selected characteristic and applications. This work explores the microstructure and the rheological behavior of hydrophobic fumed silica dispersed in a sunflower oil as a function of temperature and pressure. The results suggest that the suspensions of hydrophobic silica in sunflower oil reveals appropriate rheological and thermal properties over a wide range of temperatures and pressures to serve as components of sustainable drilling fluids.

This work explores the electrospinnability of low-sulfonate Kraft lignin (LSL)/polyvinylpyrrolidone (PVP) solutions in N,N-dimethylformamide (DMF) and the ability of the different micro- and nano-architectures generated to structure castor oil. LSL/PVP solutionswere prepared at different concentrations (8–15wt%) and LSL:PVP ratios (90:10–0:100) and physico-chemically and rheologically characterized. The morphology of electrospun nanostructures mainly depends on the rheological properties of the solution. Electrosprayed nanoparticles or micro-sized particles connected by thin filamentswere obtained fromsolutionswith lowLSL/PVP concentrations and/or high LSL:PVP ratios,whereas beaded or bead-free nanofibers were produced by increasing concentration and/or decreasing LSL:PVP ratio, due to enhanced extensional viscoelastic properties and non-Newtonian characteristics. Electrospun LSL/PVP nanofibers are able to form oleogels by simply dispersing them into castor oil at concentrations between 10 and 30 wt%. The rheological properties of the oleogels may be tailored bymodifying the LSL:PVP ratio and nanofibers content. The potential application of these oleogels as bio-based lubricants was also explored in a tribological cell. Satisfactory friction and wear results are achieved when using oleogels structured by nanofibers mats with enhanced gel-like properties as lubricants. Overall, electrospinning of lignin/ PVP solutions can be proposed as a simple and effective method to produce nanofibers for oil structuring, Funding for open access charge: Universidad de Huelva / CBUAThis work is part of a research project (RTI2018-096080-B-C21) sponsored by the MICINN-FEDER I+D+i Spanish Programme

Drilling operations performed on geothermal wells require the ongoing search for sustainable fluids that will offer maximum performance and minimum environmental impact. Therefore, studies on the replacement of traditional clay suspensions in mineral and synthetic oils with clay suspensions in vegetable oils have offered some promising results. These preliminary results suggest the need for more extensive studies, including those considering high-pressure/high-temperature (HPHT) conditions, to assess the real capacity of biodegradable oils as substitutes for mineral and synthetic oils in oil-based muds (OBM) formulations. This work analyses the structure and thermomechanical properties of commercial organo-sepiolites dispersed in vegetable oils, as a function of temperature and pressure. This serves as the principal criterion for the development of environmentally-friendly OBM for HPHT drilling applications. The results suggest that organo-sepiolites in vegetable oil suspensions have suitable thermal and mechanical properties to produce sustainable and environmentally-friendly drilling fluid for application at a wide range of temperatures and pressures.

Xanthan gum solutions have gained increasing interest for their use as environmentally friendly chemicals in the oil industry. Xanthan is compatible with most concentrate brines used for controlling formation damage and fluid loss. Particularly, formate brines reinforce the ordered structure of the biopolymer in solution, gel strength, and the specific gravity of the resulting fluid. In this paper, we studied the effect of thermal aging on the rheological behavior of xanthan solutions as a function of the concentration in potassium formate. Ionic strength below a threshold concentration does not prevent the degradation of the structure of xanthan after being submitted to aging at 165 °C. Aged solutions show an important loss of strength in their mechanical properties, lower pH, and higher content in furfural and hydroxymethylfurfural. Highly concentrated formate brines are necessary to maintain the strength of the rheological properties after exposure to high-temperature environments, This research was funded by the EU-FEDER Program, grant numbers P18-RT-4684 and CTQ-2017-89792-R

The main aim of this study was to elucidate the influence of an alkali treatment on the rheological and tribological properties, and microstructure, of cellulose pulp-based gel-like dispersions potentially usable as biodegradable lubricating greases. For this purpose, cellulose pulp was treated with sodium hydroxide under different conditions of alkali concentration (20, 30 and 40%), temperature (20, 45 and 75 °C) and contact time (1 and 2 h). Favourable conditions relative to the rheological response of a commercial lithium lubricating grease used as benchmark were found to be 40% NaOH, 20 °C and 2 h. Gel-like dispersions with acceptable lubrication properties in terms of consistency indices, mechanical stability, and frictional and wear performance, were obtained by using a 6–7% (w/w) proportion of cellulose pulp.

The aim of this work was to elucidate the influence of egg white albumen (EA) protein loaded on the electrospinning of PEO solutions under different concentrations and pHs conditions. Properties of the electrospun fiber mats, such as morphology, thermal properties, and wettability were analyzed. In addition, rheological behavior of the polymer solutions was measured to explain the electrospinnability for fiber formation. The rheological results showed that the addition of EA protein affects the molecular entanglement required to electrospin PEO, being able to incorporate up to 75wt% EA protein. The diameter of most of the PEO/EA fibers was in the range of 200-400nm. When comparing the effect of concentration and pH of the electrospinning solution, the morphology of the fibers was found to be mainly affected by the second one. FTIR analysis of the blend fibers confirmed the presence of the protein and revealed that the secondary structure changed with pH. From a thermodynamic point of view, the EA protein and PEO showed a high degree of mutual incompatibility. The presence of EA protein influenced PEO polymer thermal behavior, lowering its melting point and decreasing the quantity of PEO crystallites. All the PEO/EA electrospun fiber mats showed rapid water absorption, which increased as PEO concentration became higher, and similarly, when lowering protein concentration.

This research studies the effect of thermal, thermo-oxidative and thermomechanical degradation conditions on the melt rheological, chemical and thermal properties of PLA at temperatures around its normal processing temperature. Thermal and thermo-oxidative degradations were conducted on a rheometer by using nitrogen or air as gas, respectively, and the thermomechanical degradation was performed on a mixer equipped with two counter-rotating rollers. Dynamic oscillatory rheology, TGA, DSC and FTIR were performed on PLA samples subjected to different degradation conditions: temperature (180, 200 or 220 °C), time (15, 30 or 60 min), atmosphere (air or atmosphere) and the application of mechanical stress or not. Thus, rheological results indicate the synergic effect that temperature, mechanical stress and time exerts on the extent of chain scission phenomena, which was also corroborated by FTIR results; however, the individual contribution of mechanical stress diminishes gradually with the degradation time, being more pronounced for higher degradation temperature. In addition, degree of crystallinity (χ c ) turned out not to be a suitable parameter for comparing degraded samples, since all of them became amorphous after degradation. Instead, glass transition (T g ) and cold crystallization (T cc ) temperatures as well as the cold crystallization enthalpy (ΔH cc ) reveal that the chain scission phenomena makes degraded samples easier to crystallize. Finally, TGA results point out a worsening of the PLA thermal stability, with lower values of the characteristic temperatures (T 5% and T max ) for degraded samples.

This work has been focused on the preparation and characterization of gel-like dispersions based on sepiolite and castor oil potentially suitable as eco-friendly lubricating greases. Particularity, the effect of sepiolite content exerted on rheological, chemical, thermal and tribological properties was studied. The system exhibited a gel-like behaviour for all the concentrations considered (20–40 wt%) related to the development of a sepiolite three-dimensional colloidal network due to its characteristic nanoscale structure formed by fibers, laths and bundles. The values of both apparent viscosity and viscoelastic functions in the linear viscoelastic region increased with sepiolite content, as a consequence of a strengthening of the gel network. An empirical correlation between viscoelastic modulus and sepiolite concentration was proposed. From tribological point of view, the friction coefficient values and wear marks obtained after the frictional tests became lower when sepiolite concentrations decrease. Gel-like dispersion formulated with 30 wt% sepiolite showed appropriate rheological and tribological behaviour to be used as biolubricating greases.

The influence of concentration on the shear and extensional rheology properties of aqueous solutions of xanthan and guar gums was studied in this work. Shear rheology involved small amplitude oscillatory shear (SAOS), flow curves and transient flow, while the extensional rheology was analyzed using hyperbolic contraction flow. In addition, the mechanical properties during solutions manufacture were monitored in situ through the evolution of torque with processing time by mixing rheometry. The results showed that the hydrocolloids exert a great influence on the process rheokinetics and on the resulting rheological response. SAOS tests showed that the xanthan gum solutions behaved as weak gels, whereas guar gum solutions suggest the presence of entanglement and the formation of a viscoelastic, gel-like structure. All the systems exhibited shear-thinning behaviour. Guar gum solutions obeyed the Cox-Merz rule, with some divergence at high rates for the more concentrated solutions, while the Cox-Merz rule was not followed for xanthan gum in the range of concentration studied. The extensional viscosity exhibited an extensional-thinning behaviour within the strain range used and all solutions were characterized by a high Trouton ratio. Funding details: ceiA3

This research evaluates the effect that thermal and thermo-oxidative degradation conditions exert on the rheological, chemical and thermal properties of high-density polyethylene (HDPE). To that end, dynamic oscillatory rheology, solubility tests in xylene, TGA, DSC and FTIR were conducted on HDPE samples subjected to different degradation conditions: atmosphere (air or nitrogen), temperature (150, 175, 200, 225 or 250 °C) and time (10, 30 or 60 min). Thus, under nitrogen atmosphere, chain scission mechanism prevails over the formation of long chain branching/crosslinking phenomena, which is reflected in a decrease in complex viscosity (|η*|) and an increase in crystallinity (χ c ). Interestingly, under air atmosphere, two rheological responses were observed: a) a well-developed rubbery region, at degradation temperatures of 225 and 250 °C and, b) a so-called second “plateau” in G′ and G″, for lower degradation temperatures. Solubility tests in xylene point out that the rubbery region is consequence of both branching phenomena and the presence of crosslinking; however, the second “plateau” should be solely ascribed to the increase in the branching mechanism. In this case, the decrease in χ c is consequence of both increase in branching and formation of degradation products (accordingly supported by FTIR results). Finally, TGA results reveal that thermal and thermo-oxidative degradation shift the characteristic temperatures (T 5% and T max ) to lower values, compared to virgin HDPE.

The present work focuses on the development of lignin micro- and nano-structures obtained by means of electrohydrodynamic techniques aimed to be potentially applicable as thickening or structuring agents in vegetable oils. The micro- and nano-structures used were mainly composed of eucalyptus kraft lignin (EKL), which were doped to some extent with polyvinylpyrrolidone (PVP). EKL/PVP solutions were prepared at different concentrations (10–40 wt.%) and EKL:PVP ratios (95:5–100:0) in N, N-dimethylformamide (DMF) and further physico-chemically and rheologically characterized. Electrosprayed micro-sized particles were obtained from solutions with low EKL/PVP concentrations (10 and 20 wt.%) and/or high EKL:PVP ratios, whereas beaded nanofiber mats were produced by increasing the solution concentration and/or decreasing EKL:PVP ratio, as a consequence of improved extensional viscoelastic properties. EKL/PVP electrospun nanofibers were able to form oleogels by simply dispersing them into castor oil at nanofiber concentrations higher than 15 wt.%. The rheological properties of these oleogels were assessed by means of small-amplitude oscillatory shear (SAOS) and viscous flow tests. The values of SAOS functions and viscosity depended on both the nanofiber concentration and the morphology of nanofiber templates and resemble those exhibited by commercial lubricating greases made from traditional metallic soaps and mineral oils, This work is part of a research project (Ref. RTI2018-096080-B-C21) sponsored by the MICINN-FEDER I+D+i Spanish Programme. The authors gratefully acknowledge their financial support. J.F.R.-V. acknowledges receiving the Ph.D. Research Grant PRE2019-090632 from MICINN (Spain)

Xanthan gum solutions are used in the oil industry for flooding, drilling and completion operations. The stabilization of the structure of xanthan gum solutions in presence of salts increases the value of both the order-disorder transition temperature and the gel strength. This effect is very important in order to design drilling and completion fluids since not only density and viscosity of the fluid can be improved by increasing the concentration of salts but also the range of temperature where the solution shows viscoelastic behaviour can be extended. This paper presents results from a study on the rheological behaviour of xanthan gum solutions in different saturated brines. Chloride and formate potassium brines not only increase the viscosity of the solution but also extend the shear thinning behaviour to temperatures near 200 °C, maintaining a simple relaxation mechanism over the whole range of temperature where the ordered conformation dominates the rheological behaviour.

This work deals with the development of oleogels based on conventional (SO) and high-oleic sunflower (HOSO) vegetable oils and ethylene–vinyl acetate copolymer (EVA) for lubricant applications. Particularly, the influence of EVA concentration on the tribological, rheological properties and microstructure of these oleogels was analyzed. The results showed that the evolution of linear viscoelasticity functions was similar to that found for lithium greases. The different fatty acid profile in vegetable oils tested exerted an important influence on friction and wear in the ball-on-plates contact. The friction coefficient values became lower when EVA content was decreased. The wear marks obtained after the frictional tests for EVA–SO oleogels significantly reduced the wear scars versus EVA–HOSO oleogels and it was similar to commercial grease.

The overall objective of this work was to study the effect of reprocessing cycles of isotactic polypropylene (PP) on the rheological behavior and microstructure of gel-like dispersions in mineral oil. PP was subjected to 10 reprocessing cycles and oleogel samples were further prepared by using the mixing rheometry technique and characterized from a rheological point of view and polarized light optical microscopy (PLOM). Recycled polymer samples were also characterized by means of rheological measurements, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) to evaluate the property changes induced by reprocessing. The values of different linear viscoelastic functions (elastic modulus and complex viscosity) of recycled PP decrease with the number of reprocessing cycles, which influences oleogel rheological response. An empirical exponential correlation between the storage modulus (G′) of PP samples and the plateau modulus ( G N o ) of oleogels has been proposed to predict the rheological behavior of oleogels. Results were explained considering the scission of PP chains induced by the thermomechanical reprocessing treatment applied.

In this work, the capability of organo-bentonite (OBent)/recycled polypropylene (PP) and mineral oil blends to form gel-like dispersions potentially applicable as lubricating greases was explored. Specifically, the effect of both thickener concentration ratios on the rheology, thermal and some lubricant performance properties of the resulting gel-like dispersions was studied. The rheological response was qualitatively similar for all the samples studied and also similar to that found in standard lubricating greases. The plateau modulus G°N, of OBent/PP dispersions in mineral oil showed negative deviation from the additivity line and minimum values were observed for intermediate OBent/PP concentration ratios, excepting at the highest temperature studied (150 °C), where a continuous increase of this viscoelastic parameter with OBent content was found. The degree of crystallinity of recycled PP in the sample was influenced by the presence of OBent. Samples formulated with lower values of OBent/PP concentration ratio yield gel-like formulations with appropriate mechanical stabilities to be used as lubricating greases. The friction coefficient evaluated in a ball-on-plate tribological contact decreased with OBent content.

This work focuses on the development of gel-like formulations for use as lubricating greases. These dispersions were formulated using mineral oil and recycled/amorphous polypropylene blends. In particular, the influence of the polypropylene concentration ratio (Wi) on the rheology, thermal and some lubricant performance properties of polymer/oil blends were studied. The rheological responses of these systems were quite different, influenced mainly by the concentration of amorphous polypropylene. At intermediate temperatures (25 °C, 50 °C) and high recycled polypropylene concentrations (Wi > 0.5), the evolution of small-amplitude oscillatory shear (SAOS) functions was very similar to those found with other commercial lubricating greases. Samples with lower concentrations of amorphous polypropylene (12.5%) present maximum G N ° values in the temperature range studied. An Arrhenius-type equation can be used to quantify the thermal dependence of the linear viscoelastic functions of these gel-like dispersions. In general, sample formulations studied exhibited values of the friction coefficient comparable to those found for traditional lithium lubricating greases.

This work has been focused on the development of polyolefins/oil blends potentially suitable as lubricating greases by studying the effect that some thermo-mechanical processing variables exert on their rheological properties and microstructure. Polyolefin/oil blends have been prepared by dispersing recycled and virgin polyolefins such as high-density polyethylenes (HDPEs) and polypropylenes (PPs) in mineral lubricating oil. Linear viscoelasticity functions have been significantly influenced by processing conditions. The nature of polymers used, specially the content of HDPE, has been found to modify the microstructure of blends yielding lower mechanical stability but, on the other hand, higher values of linear viscoelastic functions.

This article deals with the influence of temperature on the rheological behavior of lithium lubricating greases modified with three different types of recycled polymers, high-density polyethylene (HDPE), low-density polyethylene, and polypropylene (PP), all deriving from waste plastic recycling plants. Grease formulations containing diverse polymers were manufactured and rheologically characterized. Small-amplitude oscillatory shear and viscous flow measurements over a temperature range of 25–175°C were carried out. The experimental results obtained suggest that a blend of HDPE and PP could be considered a suitable potential viscosity modifier for lithium lubricating greases in a wide range of in-service temperature. Thus, the lubricating greases studied modified by HDPE or PP show quite promising results at low or high temperature, respectively. In addition, thermomechanical reversibility has been studied by applying different combined stress–temperature protocols. Lubricating greases containing any of the recycled polymers studied show a significant irreversible structural breakdown when the sample is submitted to temperatures and stresses higher than 75°C and 200 Pa, respectively. Regarding lubricating grease viscous flow behavior, a minimum in the shear stress versus shear rate plots appeared at temperatures above 50°C, more pronounced as temperature increased, resulting from material flow instabilities. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers.

This work deals with the design of lubricating greases formulations based on blends of mineral oil and recycled polypropylene from postconsumer waste, coming from films with inks. In particular, the influence of polymer concentration on the rheological, mechanical, and thermal properties of recycled polymer/oil blends was characterized. From the experimental results obtained, it can be deduced that the evolution of recycled polymer/mineral oil formulations on linear viscoelasticity functions with frequency is quite similar to that found for traditional lithium greases. It is observed that these blends form systems with enhanced “plateau” modulus, G, with respect to industrial standard lubricating greases, which could be represent an important advantage, from an economic and environmental point of view. However, the influence of temperature on linear viscoelasticity functions is more pronounced than that found for traditional greases. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

This work is focused on the development of gel-like formulations, potentially applicable as biodegradable lubricating greases obtained by dispersing eucalyptus Kraft cellulose pulp, or its methylated derivative, in an ethyl cellulose/castor oil medium. The effects that concentration and weight ratio of the different cellulosic derivatives exert on the rheological properties, thermal resistance and mechanical stability of these oleogels were studied. The evolution of linear viscoelasticity functions with frequency was very similar to that found for traditional lubricating greases. In general, linear viscoelastic functions increase with Kraft cellulose pulp or methylcellulose concentrations and ethyl cellulose/Kraft cellulose pulp weight ratio. However, the relative elasticity of gel-like dispersions based on ethyl cellulose/Kraft cellulose pulp is not affected by the composition of these thickener blends, which allows the application of an empirical superposition method to obtain generalized master curves for describing the viscoelastic response of these formulations. On the contrary, the relative elasticity of methylcellulose-based gel-like dispersions depends on the composition of methylated cellulose pulp/ethyl cellulose blends. An Arrhenius-type equation can be used to quantify the linear viscoelastic functions thermal dependence of these gel-like dispersions. Moreover, formulations prepared using Kraft cellulose pulp/ethyl cellulose blends show appropriate mechanical stabilities to be used as bio-lubricating greases.

The influence that recycled low-density polyethylene (LDPE) and lithium thickener concentrations exerts on the thermal and rheological properties of lithium lubricating greases was investigated using different rheological techniques in a temperature range of 25–175°C. In this way, different lubricating grease formulations were manufactured by modifying the concentration of lithium 12-hydroxystearate and content of recycled LDPE. These lubricating greases were rheologically characterized through small-amplitude oscillatory shear (SAOS) and viscous flow measurements. In addition, bomb oxidation tests (BOTs) and thermogravimetric (TGA) analysis were carried out. From the experimental results obtained, it can be deduced that modified lithium lubricating greases can be considered thermo-rheologically complex materials. Different behaviors of the viscoelastic modulus with temperature as a function of thickener and recycled LDPE concentration were found. Two types of viscous flow behavior were observed depending...

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).

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.

The main goal of this research was to compare the modification capability of two different types of bitumen modifiers: non-reactive plastomers and elastomers, and reactive polymers. The group of non-reactive polymers included a block copolymer (SBS), recycled thermoplastic polymers (EVA/LDPE blends), and crumb tire rubber, which were mixed at a processing temperature of 180 °C. In the second group, a reactive MDI–PEG prepolymer, a low processing temperature modifier (90 °C), was considered. The study was mainly focused on the characterization of the thermorheological behaviour of selected modified bitumen samples. In addition, the thermal behaviour (by modulated DSC), and morphology (by optical microscopy) of these modified bitumen samples were also evaluated. All of these bitumen modifiers significantly improve the thermomechanical properties of the resulting binder, especially at high in-service temperatures. However, whereas bitumen modified by non-reactive polymers undergo marked oxidation events due to the high processing temperature used (180 °C), MDI–PEG modified bitumen does not experience this phenomenon because of the lower processing temperature involved (90 °C). In general, non-reactive polymers should be added in much larger concentrations than the reactive polymer to obtain similar results, although the latter requires a further period of curing, at room temperature, to induce suitable modification. Finally, only MDI–PEG modified bitumen is stable when stored at high temperature (163 °C), whereas all the non-reactive polymer-modified bitumen studied undergo either phase separation or particle precipitation.

Reactive polymers are lately gaining acceptance to give added value to a residue of the crude oil refining process such as bitumen. The resulting material should display enhanced mechanical properties to be considered for advanced applications in construction. In the present paper, we report the effect of processing temperature on the reaction between bitumen compounds and an isocyanate-based reactive polymer, synthesized by reaction of polymeric MDI (4,4′-diphenylmethane diisocyanate) with a low molecular weight polyethylene-glycol (PEG). Rheokinetics experiments, viscosity measurements at 60 °C, atomic force microscopy (AFM) characterization, thin layer chromatography (TLC-FID) analysis and thermogravimetric studies (TGA) were performed on the reactive polymer and on samples of MDI-PEG modified bitumen containing 2 wt.% of the polymer. Results showed the existence of an optimum processing temperature arisen as a consequence of opposite effects: microstructural availability for the formation of a polymer–bitumen network, reaction ability and polymer thermal degradation. Consequently, this study aims to serve as a guideline for the refining and asphalt industries facing the stage of selecting the optimum processing parameters.

There is a growing interest on the development of new materials based on recycled polymers from plastics waste, since the use of such plastics represents a low-cost source of raw material. The purpose of the present work is to evaluate, from a comparative point of view, the effect that different waste and virgin polymers, used as viscosity modifier additives, exert on the rheological properties of standard lithium lubricating greases. Grease formulations containing diverse polymers, differing in nature and/or origin, were manufactured and rheologically characterized. Particularly, the influences of the type of polymer, the molecular weight and the presence of carbon black, used as filler in recycled polymers, have been evaluated. Small-amplitude oscillatory shear (SAOS) and viscous flow measurements were carried out, as well as calorimetric and thermogravimetric analysis. In general, recycled polymers induce a more important rheological modification than virgin polymers of the same nature. Thus, the addit...

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

In this study, the suitability of a reactive polymer, synthesized by reaction of 4,4′-diphenylmethane diisocyanate (MDI) with a low molecular weight polyethylene-glycol (PEG), as a modifying agent for the manufacture of bitumen-based waterproof membranes, was evaluated. With that purpose, rheological and thermal analysis tests, and microstructural observations by AFM were carried out on different samples of modified bitumen having a MDI–PEG content ranging from 0 to 10 wt.%, cured at room temperature for a period of time within 0–30 days. The results obtained demonstrate that the addition of the reactive polymer proposed in this work to bitumen is very suitable at high in-service temperatures, because a noticeable increase in the values of viscosity, at 60 °C, of the resulting modified bitumen samples is observed on a time-scale of days. AFM observations, carried out at 50 °C, evidenced that the reactive polymer MDI–PEG leads to a new microstructure, displaying a higher level of stiffness. Therefore, this polymer should be seriously taken into consideration as a modifier of bituminous coatings for the waterproofing industry.

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.

This work deals with a rheological study of oleogels based on high-oleic sunflower oil (HOSO) and ethylene vinyl acetate copolymer (EVA) / isotactic polypropylene (iPP) blends. EVA copolymers with different vinyl acetate content were used. With this aim, linear small amplitude oscillatory shear (SAOS) and nonlinear (relaxation) measurements combined with polarized optical microscopy were carried out. Oleogels were prepared by using the mixing rheometry technique in a batch mixer. Oscillatory strain amplitude sweep tests showed that the end from the viscoelastic linear region for oleogels was accompanied by opposite trends for viscoelastic moduli. SAOS tests showed that all the oleogels present similar behavior characteristic of polymeric systems with physical entanglements. It was found that the elastic equilibrium modulus and loss tangent increases with iPP content. On the other hand, nonlinear relaxation tests presented a strong dependence on the strain applied and the Soskey–Winter model was found to provide an accurate description of the damping function of these oleogels. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42477.

Transportation and consumption of petroleum products around the world have created a potential risk for oil spills in the environment. Knowledge of high-pressure rheological behaviour of heavy crude oil fractions, which are usually transported in oil tankers, is very important to design deep recovering operations of the oil remaining in the tanks after an accident. The effect of pressure on the viscosity of these materials is not well understood, this is mainly due to experimental constraints involving high-pressure rheology measurements at low shear rates. Consequently, the overall objective of this work is to model the temperature–pressure–viscosity dependence of a selected heavy fuel oil in a wide range of pressure and temperature. With this aim, viscous flow tests at different temperatures and differential pressures and modulated differential scanning calorimetry tests were carried out on the heavy fuel oil selected. A temperature–pressure–viscosity model (FMT model) fits fairly well the experimental results obtained in the whole differential pressure range studied. However, viscosity values at temperatures lower than 10°C cannot be predicted due to microstructural changes associated with the solidification process of the heaviest components of the fuel oil tested.

The development of some cellulose pulp gel-like dispersions in castor oil with application as biodegradable lubricants was explored in this work by analyzing the effect that Kraft cellulosic pulp cooking conditions exerts on the rheological properties and mechanical stability of these formulations. With this aim, Eucalyptus globulus cellulosic pulps were obtained by increasing the pulping time at the maximum temperature, yielding H factors ranging from 150 to 500. Gel-like dispersions of cellulosic pulps in castor oil were prepared and characterized from a rheological point of view. Small-amplitude oscillatory shear (SAOS) measurements and some standard mechanical tests, usually performed on commercial lubricating greases, were carried out in order to evaluate the lubricant performance of these dispersions. In general, the values of linear viscoelastic functions increase with the H factor. Cellulose pulps submitted to lower H factors provides gel-like dispersions with SAOS functions values more similar to those found in traditional lubricating greases. Results were explained attending to a balance between the cellulose polymerization degree and lignin and α-cellulose contents, all of them affected by the H factor applied. An empirical correlation between these variables and both the plateau modulus and the loss of consistency has been proposed to predict the rheological behavior and mechanical stability of gel-like cellulose pulp dispersions in castor oil. © 2012 American Chemical Society.

This work deals with the effect that some processing variables and type of mineral lubricating oil (naphthenic and paraffinic) used exert on the rheological properties of lubricating greases modified with recycled polymers. In particular, the optimisation of recycled polymer addition at different lubricating grease processing stages and cooling profiles were studied. The influence of processing variables was evaluated by performing small-amplitude oscillatory shear (SAOS), viscous flow and thermal analysis tests. From the experimental results obtained, it may be concluded that the addition of recycled polymer significantly increases the values of linear viscoelasticity functions, especially when added immediately after the saponification reaction, during the heating stage, or at the beginning of the cooling stage (180°C). A combined stepwise cooling ramp, first at a high rate and then at a low rate, is more effective to achieve higher values of the rheological functions than the application of constant cooling rates in the final processing stage. The values of the rheological functions decrease as base oil viscosity increases and increase when using a naphthenic instead of a paraffinic oil of similar viscosity.