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The present study addresses the immobilization of the GOX enzyme into a conventional polyvinyl alcohol (PVOH) membrane and a multi-layer membrane system (PCL/PVOH/PCL), both synthetized through electrospinning technique. More specifically, the enzyme was encapsulated inside a PVOH hydrophilic membrane, which was in turn protected by two hydrophobic polycaprolactone (PCL) membranes (multilayer system). The manufactured systems were characterized through IR spectroscopy, enzymatic kinetics and mechanical properties. Moreover, the morphology of the fibers composing the membranes was studied by Scanning Electronic Microscopy (SEM) and image analysis. Finally, the enzyme activity of the systems was in-vitro bacterial cultures using E. coli. The results obtained indicate that the addition of the GOX enzyme involves a slight reduction of the mechanical properties (maximum strain at break and maximum stress), which is associated with an increase of the polydispersity of the generated fibers. However, the mats showed antibacterial properties, which were evidenced by the inhibition of E. coli growth. These results indicate that this technique is suitable for the immobilization of enzymes with potential use in the active packaging industry.

This study investigates the development of novel montmorillonite/castor oil blends to formulate sustainable lubricating greases to promote the replacement of petrochemicals industry-derived materials by substances obtained from renewable sources. Specifically, the effect of the thickener concentration on the rheological, chemical, thermal, tribological properties, and atomic force microscopy (AFM) microstructure of these systems were studied. The results showed that the C20A nanoclay content could be used to modulate the viscosity values, the linear viscoelastic functions, and tribological properties of these montmorillonite dispersions. In general, these gel-like dispersions exhibited remarkable lubricant properties; the samples showed values of the friction coefficient and wear scars similar or lower than those obtained with model bentonite grease.

Nowadays, there is a marked tendency in order to develop new composite fibers based on proteins and polysaccharides due to these materials can exhibit a wide range of tailored functional properties. In this framework, this study has been focused on the development of novel potato protein (PP)-based composite fibers by electrospinning technique using formic acid as solvent media. At the selected electrospinning conditions, PP pure solutions (3–8 wt.%) showed inadequate spinnability. Interestingly, the addition of polyethylene oxide (PEO) as co-blending polymer improved the solutions viscoelasticity and hence, the solutions spinnability. Composite fibers with enhanced properties were obtained at higher PEO concentrations while systems with higher PP protein contents led to electrosprayed separate aggregates of particles. Fourier-transformed infrared spectroscopy and thermogravimetric analysis results showed that the obtained composite fibers were composed of both PP and PEO materials. DSC results show that PP influences on PEO polymer thermal behaviour lowering its melting point, and an increase of the PEO amount produces a decrease of the α-helix denaturation temperature. Due to the properties of PP and PEO, these novel composite fibers could find importance in a diverse range of applications as advanced functional materials in fields like food science and biomedical applications.

Some of the most important engineering skills required nowadays are related with the management of computational tools. This study proposes the implementation of a novel teaching methodology for improving the calculation of pumping power by using the Mathcad software. This methodology includes: (1) training courses on initiation to Mathcad, (2) the delivery of a report with theoretical considerations about pumping power, the problem statement, the traditional procedure to solve it, as well as the main indications to do it with Mathcad, and (3) a virtual platform conceived as a meeting space. The assessment of this educational experience, which was carried out with the second-year chemical engineering students enrolled in the Fluid Flow course, revealed that Mathcad is a powerful computational tool for them. Thus, it eliminates the mathematical difficulties, facilitates the understanding of the phenomenon under consideration and the study that the input variables exert on the solution, and also increases the motivation of the students for solving other engineering problems. Therefore, these results support the hypothesis that computational tools like Mathcad direct chemical engineering students towards successful learning.

This work has been focused on the fabrication and characterization of polyvinylpyrrolidone (PVP)/tragacanth gum (GT) fibers prepared by electrospinning technique. The influence of GT amount on the electrospinning of PVP aqueous solutions under different concentrations was studied. Spectroscopic (FTIR and XPS), morphological (SEM) and thermal (DSC and TGA) properties of the electrospun fiber mats were analyzed. In addition, rheological behavior of the polymer solutions was measured to explain the electrospinnability for fiber formation. The results of SEM showed that the GT content exerts an important influence on the fiber morphology. The fiber diameter increased with increasing PVP concentration, whereas the diameter of fibers increased with decreasing GT concentration. One empirical correlation between the diameter of the fibers and the Newtonian viscosity has been proposed. Chemical analysis confirmed the presence of GT in fiber composition and the results of DSC proved that GT influences PVP polymer thermal behavior.

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

The overall objective of this work was to study the combined effect of hydrogen peroxide (H2O2) and light emitting diodes (LED) process assisted by titanium dioxide (TiO2) on the photo-oxidation behaviour of polylactic acid (PLA). The photochemical behaviour of PLA in a TiO2 suspensions was studied by irradiation under photo-oxidative conditions (λ > 454 nm, ambient temperature and with or without the presence of H2O2). The chemical and thermal properties induced by LED irradiation process were analyzed using fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H NMR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). It was found that the presence of photoactive TiO2 particles, combined with H2O2 leads to strong impact on the physicochemical properties of the samples during photochemical ageing. A new comprehensive mechanism for the photo-oxidation of PLA for these conditions was discussed.

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.

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

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.

Nowadays, environmentally friendly cutting fluids should be applied in manufacturing processes. Concretely, in many machining processes the use of minimum quantity of lubrication (MQL) is established as common routine. In this paper, the use of natural biodegradable oils as an alternative to traditional canola oils used in MQL is analyzed, comparing five different alternatives (i.e.: sunflower oil, high oleic sunflower oil, castor oil and ECO-350 recycled oil). Firstly, the aim is to evaluate the feasibility of the proposed oils, just analyzing their tribological and rheological characteristics. Secondly, a full battery of experimental tests was performed in order to validate their behavior during cutting Inconel 718, a difficult-to-cut material commonly used in aeronautical components. Finally, life cycle assessment was carried out with the aim of analyzing their environmental feasibility. Results show that the combination of low viscosity with high friction coefficient implies an increase in tool life. In this line, ECO-350 recycled oil presents a feasible behavior and improves the tool life up to 30% in comparison with commercial canola oil. However, its recycling process has to be improved from an environmental point of view. Taking both issues, high oleic sunflower oil presents a balance between them. On one hand, it improves tool life (15%) and on the other hand, similar environmental impact is obtained compared with canola oil. This supposes an advance, being more efficiently, not only environmentally speaking but also technically.

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)

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.

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.

A combination of crayfish flour (CF, with 60% protein) and Polycaprolactone (PCL) was successfully used to prepare biocomposites by a process that consists of two stages: mixing with glycerol (GL) as plasticizer and injection moulding of CF/GL/PCL blends. Mixing rheometry and Differential Scanning Calorimetry (DSC) measurements were found to be useful to select suitable injection moulding conditions. A remarkable enhancement in mechanical properties was found for PCL containing systems, even when crystalline structure remains unaltered. PCL yields a dominant contribution to the elastic response and confer a higher ability to absorb energy before rupture, but also the protein/plasticiser ratio must be considered.

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.

New oleogel formulations based on high-oleic sunflower oil (HOSO) and ethylene vinyl acetate copolymer (EVA)/polypropylene (PP) blends were prepared using the mixing rheometry technique and further characterized. The effects of PP tacticity and EVA vinyl acetate (VAc) content on the rheological, morphological, and thermal behavior of derived oleogels were investigated. Differential scanning calorimetry (DSC) and polarized-light optical microscopy (PLOM) observations indicated that VAc segments markedly influence the crystalline structure of polymeric fractions and phase morphology of oleogels. The normalized crystallinity of isotactic polypropylene (iPP) phase increased linearly with its concentration whereas syndiotactic polypropylene (sPP) content does not exert a significant influence. PLOM observations showed that VAc content plays an important role in the phase morphology of PP frictions (size and shape of crystals). The viscoelastic response of oleogels depended on PP tacticity and VAc content, which may be explained attending to the different microstructures attained. POLYM. ENG. SCI., 55:1429–1440, 2015. © 2015 Society of Plastics Engineers

The overall objective of this work was to study the influence of vinyl acetate (VAc) content on the rheological properties and microstructure of polymer gels based on conventional and high-oleic sunflower vegetable oils and ethylene-vinyl acetate copolymer (EVA). The mechanical properties during gel preparation can be in situ monitored through the evolution of torque with processing time by using the mixing rheometry technique. Linear viscoelastic measurements, as well as differential scanning calorimetry (DSC) tests and morphological observations, were performed on the resulting gels. From the experimental results, it can be concluded that VAc content and melt flow index of the EVA copolymer significantly affect the rheological and thermal responses of polymer gels. VAc content, mainly affecting EVA degree of crystallinity, and melt flow index influence the linear viscoelastic behaviour in opposite directions. On the contrary, the extension of the linear viscoelastic regime and gel-like to liquid-like response transition temperatures are mainly dominated by EVA degree of crystallinity, as confirmed through calorimetry tests and microscopy observations. The different fatty acid profile in sunflower oils tested does not exert an important influence on process rheokinetics and rheological behaviour.

In this study, albumen/chitosan (EA/CH) based biocomposites were successfully prepared using injection moulding method. In particular, the influence of CH as physicochemical modifier additive in composite materials with EA protein matrix in different concentrations in the range of 0–40 wt.% were considered. Biocomposites from EA/CH were characterised by Fourier transform infrared spectroscopy (FTIR), thermal analysis and Confocal Laser Scanning Microscopy (CLSM). Dynamic Mechanical Thermal Analysis (DMTA), tensile properties, water absorption capacity and standard tests to assess antimicrobial activities of the composites were also evaluated. FTIR analysis showed no new chemical bonds, suggesting that there was no chemical reaction and that the interaction was weak between the two biopolymers. DMTA spectra were qualitatively similar for EA/CH biocomposites, and comparable to commercial low density polyethylene (LDPE). The incorporation of CH particles led to less stiff and less elastic composites. Thermal properties of albumen composite were affected by CH addition. Water absorption capacities of the modified composites were smaller than neat albumen composite.

Biobased plastics from renewable polymers constitute a highly interesting field for relevant industrial applications such as packaging, agriculture, etc., in which thermomechanical techniques (i.e. extrusion, compression molding, etc.) are increasingly being used. In spite of the potentials of injection molding in the manufacture of shaped products it is still scarcely used with biopolymers. This study evaluates injection molding as an alternative to produce biobased materials from blends prepared in a mixing rheometer, using different albumen/soy ratios and glycerol as the plasticizer. Viscoelastic measurements and DSC of protein/glycerol blends were used to select suitable processing conditions. Physicochemical properties of injection-molded probes were characterized through dynamic mechanical thermal analysis, tensile strength, water uptake and transmittance tests. Occurrence of shear-induced effects over mixing was confirmed by extractability analysis of protein concentrates and blends, particularly for soy-based systems. Both proteins and their mixtures yield injection-molded bioplastics, although showing lower mechanical properties than LDPE standards.

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.

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

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.

In this work, the use of different cellulosic pulp samples to prepare new formulations potentially applicable as biodegradable lubricating greases is explored. Cellulosic pulps from different raw materials and submitted to different pulping process and/or several acidic treatments were characterized and used as biothickener agents to formulate gel-like dispersions. Cellulose pulp samples mainly differed in polymerization degree (160-893 cm3/g) and lignin (0.3-27.1% w/w) and α-cellulose (46.0-85.1% w/w) contents. Rheological measurements and some standard mechanical tests usually performed with lubricants were carried out. The rheological response of cellulosic pulp-based gel-like dispersions is mainly a consequence of the balance between the cellulose polymerization degree and lignin and α-cellulose contents, independently on the origin of cellulose samples and pulping treatment. An empirical correlation between a power function of these variables and the plateau modulus has been proposed to predict the rheological behavior of resulting formulations. However, cellulosic pulp-based dispersions studied generally present either poor mechanical stability or low consistency indexes than expected for lubricating greases. © 2011 American Chemical Society.

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.