Assessment of the Tribological Performance of Electrospun Lignin Nanofibrous Web-Thickened Bio-Based Greases in a Nanotribometer

The tribological performance of novel bio-based lubricating greases thickened with electrospun lignin nanostructures was investigated in a nanotribometer using a steel-steel ball-on-disc configuration. The impact of electrospun nanofibrous network morphology on friction and wear is explored in this work. Different lignin nanostructures were obtained with electrospinning using ethylcellulose or PVP as co-spinning polymers and subsequently used as thickeners in castor oil at concentrations of 10-30% wt. Friction and wear generally increased with thickener concentration. However, friction and wear decreased when using homogeneous bead-free nanofiber mats (with higher fiber diameter and lower porosity) rather than nanostructures dominated by the presence of particles or beaded fibers, which was favored by reducing the lignin:co-spinning polymer ratio.This work is part of a research project (PID2021-125637OB-I00) funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe” (EU). The financial support is gratefully acknowledged

Reología de la fase líquido-cristalina laminar en siste- mas alcohol polietoxilado/agua/heptano.

En este trabajo se han estudiado las propiedades reológicas de una fase líquido-cristalina laminar contenida en un sistema al- cohol polietoxilado/agua/heptano, mediante ensayos viscoelásti- cos lineales, estacionarios y transitorios. El efecto de distintas variables como la composición de tensioactivo y heptano sobre dichas propiedades reológicas ha sido analizado. El espectro me- cánico obtenido de la fase laminar muestra en todos los casos una región «plateau» en el intervalo de frecuencias estudiado así como mayores valores de los parámetros viscoelásticos para va- lores intermedios de la concentración de tensioactivo y heptano, indicativo de un mayor desarrollo del entramado elástico estructu- ral de dicha fase líquido-cristalina. Los ensayos de flujo estaciona- rio y transitorio pusieron de manifiesto la existencia de estructuras inducidas por cizalla. En las curvas de viscosidad se obtuvieron diferentes regiones de variación potencial de la viscosidad frente a la velocidad de cizalla y, por tanto, distintos valores de índices de flujo. Las modificaciones de la microestructura de la fase líqui- do-cristalina laminar causadas por la cizalla, fueron confirmadas mediante el uso de microscopía de luz polarizada en un sistema de cizalla que incorpora un microscopio óptico. Las modificacio- nes estructurales parecen estar muy influenciadas por la veloci- dad de cizalla y, generalmente, la aplicación de elevadas velocidades de cizalla provoca el alineamiento de las bicapas de tensioactivo y la aparición de la clásica textura de «oily streaks» de la mesofase laminar. La presencia de vesículas se detecta en sistemas con alto contenido en heptano, como indica la textura detectada por microscopía de luz polarizada.Linear viscoelastic tests as well as transient and steady flow experiments were carried out on lamellar liquid crystalline samples of poly(oxyethylene) alcohol/water/heptane systems. The effect of surfactant and heptane concentrations on the rheological properties of the lamellar mesophase was investigated. The mechanical spectrum inside the linear viscoelastic regime shows, in all cases, a well-developed plateau region in the whole frequency range studied. The values of the dynamic functions were higher for intermediate surfactant or heptane concentrations indicative of a major development of the elastic network in the midrange of existence of the lamellar phase. Transient and steady flow experiments point out a shear-induced evolution of the lamellar microstructure. Different power law regions with different values of the flow index were detected in the viscosity versus shear rate plots. These shear-induced structural modifications were confirmed by using polarizing microscopy in an optical shearing cell. Structural modifications appear to be highly influenced by shear rate. In general, applying relatively high constant shear rates, the alignment of the bilayers followed by the appearance of the «oily streaks» structure was observed. Appearance of shear-induced vesicles occurs at high heptane content, as indicates the texture of close-packed monodisperse spherulites detected by polarizing microscopy

Thickening Castor Oil with a Lignin-Enriched Fraction from Sugarcane Bagasse Waste via Epoxidation: A Rheological and Hydrodynamic Approach

Thickening vegetable oils to different extents is of great interest in the design and development of new bio-based lubricant formulations, as achieving a wide range of rheological properties is crucial to the successful replacement of petroleumbased traditional counterparts. With this aim, the influence of epoxidation degree, modified by altering the reaction conditions, on the viscous flow properties of epoxidized castor oil was investigated together with the incorporation of a lignin-enriched fraction from sugarcane bagasse waste to more extensively modify the rheological properties, thereby valorizing this waste fraction. Oil thickening was achieved by promoting the cross-linking between the epoxidized oil and the lignin-enriched fraction that enables the compatibilization of both components. Castor oil epoxidation was assessed by means of standard volumetric titration methods and infrared spectroscopy. In addition, a fully rheological characterization of both epoxidized and lignin-thickened castor oils was carried out. A hydrodynamic approach was also followed, aiming to provide an estimation of the Mark−Houwink−Sakurada parameters and relate the intrinsic viscosity with the average molecular weight of the resulting epoxidized castor oil/lignocellulose macromolecular compounds. The chemical interaction between castor oil and the lignocellulosic material increased as the extent of epoxidation was increased, yielding a variety of rheological responses from Newtonian liquids of increasing viscosities (from around 1 to 500 Pa·s) to viscoelastic liquids.This work is part of a research project (RTI2018-096080-B- C21) sponsored by the MICINN-FEDER I+D+i Spanish Programme. The financial support is gratefully acknowledged. The authors are also grateful to Dr. Ignacio Ballesteros (CIEMATMadrid, Spain) for kindly providing the ligninenriched waste fraction used in this study.Funding for open access charge: Universidad de Huelva / CBU

Influence of surfactants on the electrospinnability of lignin‑PVP solutions and subsequent oil structuring properties of nanofiber mats

This work focuses on the improvement of the electrospinnability of low-sulfonate lignin (LSL)/polyvinylpyrrolidone (PVP) solutions by the addition of surfactants (SDS, CTAB and Tween-20) as well as on the ability of resulting nanofibers to structure castor oil. Solutions with two LSL/PVP weight ratios (70:30 and 90:10) in DMF were prepared by adding variable surfactant concentrations (0–1 wt.%), and physicochemically characterized. Electrical conductivity, surface tension and rheological measurements were performed. Variations of these physicochemical properties were explained on the basis of surfactant-polymer interactions. The addition of surfactants to LSL/PVP solutions improves electrospinnability, producing more compact and uniform fiber mats in 70:30 LSL/PVP systems, generally reducing the average diameter of the nanofibers and the number of beads. In contrast, nanofiber mats were not obtained with 90:10 LSL/PVP solutions, but different nanostructures composed of particle clusters. Dispersions of nanofiber mats obtained by electrospinning from 70:30 LSL/PVP solutions in castor oil were able to generate physically stable strong oleogels. In general, linear viscoelastic functions of oleogels increased with surfactant concentration. In addition, these oleogels exhibited excellent lubrication performance in a tribological contact, with extremely low values of the friction coefficient and wear diameters, which may lead to potential applications as lubricants.Research project (RTI2018-096080-B-C21) funded by MCIN/ AEI/10. 13039/ 501100011033 and by “ERDF A way of making Europe.” Funding for open access charge Universidad de Huelva/CBU

Electrospun lignin-PVP nanofibers and their ability for structuring oil

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 structuringThis work is part of a research project (RTI2018-096080-B-C21) sponsored by the MICINN-FEDER I+D+i Spanish ProgrammeFunding for open access charge: Universidad de Huelva / CBU

Impact of the Morphology of Electrospun Lignin/Ethylcellulose Nanostructures on Their Capacity to Thicken Castor Oil

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 Programm

Estudio sobre el uso e integración de plataformas de teleformación en universidades andaluzas

Hoy es ya una realidad incuestionable el papel preponderante que ocupan las tecnologías en todos los aspectos de la vida en general, y en la educación en particular. El conocimiento y accesibilidad de estos recursos eliminan barreras espacio-temporales, permitiendo que el e-learning o la teleformación se con-viertan en herramientas de gestión del conocimiento. En el terreno universitario, el e-learning está en continuo crecimiento y ya son muchas las universidades que poseen campus y cursos virtuales. Esta modalidad educativa on-line necesita de un espacio de aprendizaje en el que desarrollarse. Dicho espacio se ha conformado en las llamadas plataformas de teleformación, que están experimentando un crecimien-to muy notable, tanto en su dimensión comercial como en la de código libre. Este proyecto pretende ana-lizar estas plataformas de gestión del conocimiento educativo, determinando virtualidades y limitaciones, así como diseñar herramientas informáticas que permitan a los usuarios el análisis comparativo de las mismas en su doble versión. La implementación en grupos experimentales de las Universidades andalu-zas, finalmente, nos permitirá obtener información contrastada sobre las posibilidades de estos nuevos recursos formativos telemáticos.The importance of technologies in all aspects of modern life, and in education in particular, is indisputable. The knowledge and accessibility offered by these resources are breaking down time-space barriers, and e-learning or virtual learning are now tools of knowledge management. At university, e-learning continues to expand, and many now have their own virtual courses and campuses. This online education modality requires a space for learning in which to develop, which is occupied by virtual learning platforms that are increasing rapidly in their commercial and open code forms. The aim of this study is to analyse these platforms of educational knowledge management, specifying their virtual qualities and limitations, and to design computer tools that allow the user to make a comparative analysis of these commercial and open code platforms. The experimental implementation of virtual learning platforms among student groups at universities in Andalusia allows us to extract information about the opportunities offered by these new e-learning resource

La motivación del alumnado como eje vertebrador en la era Post-MOOC

La evolución de MOOC en la última década ha significado una revolución en la formación abierta del alumnado en el contexto universitario. Diversidad de temáticas, experiencias y multitud de equipos multidisciplinares e interuniversitarios trabajan en la planificación, integración y mejora de este recurso con fin formativo en la educación superior. La producción científica sobre esta línea de investigación en el plano de la tecnología y la educación también ha sido muy fructífera en este intervalo temporal de expansión y consolidación, aunque consideramos que queda mucho por avanzar en aportaciones críticas que proyecten y permitan avanzar en la era post-MOOC. El eje central que nos propusimos en este estudio fue conocer las motivaciones que incitan al alumnado a la hora de participar en estas propuestas formativas, su grado de satisfacción y su intención de continuar avanzando en esta línea. Nuestros resultados evidencian que esta modalidad de aprendizaje posee ventajas valoradas muy positivamente por las personas que acceden a ellos y es considerada una experiencia atractiva y amena, que influye en la decisión de volver a cursarlos.

Fourier state of a fluidized granular gas

It is shown that the Boltzmann equation for smooth inelastic hard disks or spheres admits a solution describing a steady state characterized by uniform pressure and linear temperature profile. Such a state has been observed previously both in numerical solutions of the Boltzmann equation and in molecular dynamics simulations. Quite peculiarly, pressure and temperature gradient are not independent but their ratio is a function of the coefficient of restitution. Several properties of the solution are discussed. In particular, it is shown that a linear Fourier-like law is verified for arbitrary temperature gradient.Grant No. PB98-1124 from the Dirección General de Investigación Científica y Técnica (Spain)

Electrohydrodynamic Processing of PVP-Doped Kraft Lignin Micro- and Nano-Structures and Application of Electrospun Nanofiber Templates to Produce Oleogels

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 oilsThis 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