On the phase affinity of multi-walled carbon nanotubes in PMMA:LDPE immiscible polymer blends.

The localization of multi-walled carbon nanotubes (MWCNTs) in PMMA/LDPE blends was studied. Theoretical predictions suggested their preferential localization in the PMMA. Conversely, experimental work revealed that non-functionalized MWCNTs located in the LDPE, polymer first to melt. When the extrusion time is not long enough, the MWCNTs do not have the chance to further migrate to the thermodynamically most favourable phase. The evolution of a double percolation determined if the composite became semi-conductive. In that sense, two blends with PMMA to LDPE ratios of 80:20 and 20:80 containing 2 wt.% MWCNTs had electrical resistivity values in the order of 105 and 1012 Ω cm, respectively. Only in the 80:20 blend was the “effective” MWCNT concentration high enough such that electrical percolation was attained. However, bulk rheological properties were controlled by the major phase. Thus, 2 wt.% MWCNTs had a notable effect on the linear viscoelasticity at low frequencies of the 20:80 blend

Análisis de la situación de los estudiantes de Comunicación para el Desarrollo del V año vespertino en el contexto del ejercicio de sus Prácticas Profesionales I, de la UNAN-Managua, durante el II Semestre 2019

En la presente monografía, se busca conocer de una manera más amplia el desarrollo de las Prácticas Profesionales I, en los estudiantes del V año turno vespertino, puesto que, pasan a ser la muestra de la investigación en estudio, el documento tendrá los resultados de acuerdo a experiencias que se podrán percibir en la aplicación de los instrumentos como en el caso de las encuestas y del grupo focal, como métodos para la obtención de información, así mismo, debilidades, necesidades, habilidades y dirección metodológica que pudieron experimentar en el momento de atravesar el proceso de las Prácticas Profesionales I. Con el fin de obtener resultados verídicos, e importante por ser parte del elenco protagónico de dicho fenómeno en estudio, se procedió a entrevistar al coordinador de la carrera a la que pertenece la población y muestra, además a una de las tutoras quienes han impartido y han estado a cargo de esta asignatura, y finalmente y a un supervisor o responsable de los practicantes en un medio de comunicación, medio que le ha facilitado por años la inserción de pasantes a la universidad. Para efectos de investigación se trabajará bajo el tema: “Análisis de la situación en los estudiantes de Comunicación para el Desarrollo, del V año del turno vespertino, en la realización de sus Prácticas de Profesionalización I, de la UNAN-Managua, durante el II Semestre 2019”. Cabe mencionar que en el fenómeno en estudio, será hará evocación del Reglamento del Régimen Académico Estudiantil de la UNAN-Managua y la regulación en cuanto al tema de las Prácticas Profesionales. Palabras claves: Prácticas Profesionales, debilidades, necesidades, habilidades, dirección metodológica, reglamento

Effect of shear processing on the linear viscoelastic behaviour and microstructure of bitumen/montmorillonite/MDI ternary composites

Polymer modified bitumens (PMBs) have largely been utilized as a construction material. However, lack of affinity between bitumen and polymer leads to phase separation, and eventually, performance depletion. In this paper, alternative formulations of bitumen with an organically-modified montmorillonite (OMMT) Cloisite 20A® and polymeric methylene diphenyl diisocyanate (MDI) were prepared by melt blending. Their comprehensive rheological characterization evidenced improved linear viscoelastic properties when OMMT is added, revealing a noticeable structural reinforcement and thermal stability. Rheological data also showed that MDI-involved reactions control the composite end properties, being greatly influenced by the shear conditions applied

Influence of tragacanth gum in egg white based bioplastics: Thermomechanical and water uptake properties

This study aims to extend the range of applications of tragacanth gum by studying its incorporation into bioplastics formulation, exploring the influence that different gum contents (0–20 wt.%) exert over the thermomechanical and water uptake properties of bioplastics based on egg white albumen protein (EW). The effect of plasticizer nature was also evaluated through the modification of the water/glycerol ratio within the plasticizer fraction (fixed at 40 wt.%). The addition of tragacanth gum generally yielded an enhancement of the water uptake capacity, being doubled at the highest content. Conversely, presence of tragacanth gum resulted in a considerable decrease in the bioplastic mechanical properties: both tensile strength and maximum elongation were reduced up to 75% approximately when compared to the gumfree system. Ageing of selected samples was also studied, revealing an important effect of storage time when tragacanth gum is present, possibly due to its hydrophilic character.Ministerio de Economía y Competitividad (MAT2011-29275-C02-01

Exploring the effect of the pulp bleaching on the thermo-rheological behavior of sustainable cellulose nanofiber-based oleogels

Taking advantage of the high thickening capacity of cellulose nanofibers in castor oil, sustainable lubricating oleogels were obtained. Methanol was used as mediator to transfer the nanofibers, originally present as a hydrogel, into the vegetable oil. The effect of the pulp bleaching on the oleogels’ thermo-rheological behavior was analyzed. Viscous flow curves and small/large amplitude dynamic shear tests were carried out on both bleached and unbleached samples of the same elm kraft pulp. Substantial differences were observed, above all when the oleogels were subjected to stress values beyond the onset of their linear viscoelastic regimes. The oleogel prepared with nanofibers from the unbleached pulp was found to endure large shear deformations better than that from the bleached pulp, and was less sensitive to temperature. Hence, the complex shear modulus (|G*|) corresponding to the oleogel based on 1.4 wt% bleached nanofiber decreased by 55.7% upon a non-linear stress of 200 Pa was applied for 30 min. However, a less severe structural breakdown, i.e., a decay in |G* | of 28.9% (half of the previous one), was monitored when the oleogel based on the unbleached nanofiber was submitted to the same testing conditions. It should also be underlined that such an oleogel showed an extraordinary capacity to recovery its structure after the large shear deformation process.This work is part of two Research Projects sponsored by “Programa Operativo FEDER-Andalucía 2014–2020 ′′ (UHU-1255843 and UHU- 202008). Funding for open access charge: Universidad de Huelva/ CBUA. The authors gratefully acknowledge their financial support. S.D. Fern´andez-Silva acknowledges “Ayudas para la Contrataci´on Predoctoral de Personal Investigador en Formaci´on 2021, Junta de Andalucía” (PREDOC_01696), for funding his PhD Thesis

Food Sovereignty in the city?: A methodological proposal for evaluating food sovereignty in urban settings

Although the possibility of achieving food sovereignty in urban environments is controversial, we believe that food sovereignty is attainable. In this work we propose a methodology for evaluating it, then test that proposal using San Cristóbal de Las Casas as a case study. For this purpose, we used a participatory methodology to construct a system of food-sovereignty indicators for urban settings. After review and validation by participants and a group of experts, that system consisted of 30 indicators. We tested it by using it to survey households in San Cristóbal. We found that the set of 30 indicators is coherent with the principles of food sovereignty, and that it enabled us to reveal the alimentary vulnerability of the city’s families. We hope that the principles that form the basis for the proposed methodology will be applicable when designing instruments for assessing other cities’ levels of food sovereignty.This work was supported by the Consejo Nacional de Ciencia y Tecnología [561556/307908]

Bitumen chemical modification by thiourea dioxide

This work evaluates a novel bitumen modification through the use of a chemical agent, thiourea dioxide, substance which has been traditionally used as a reducing agent. Thermogravimetric analysis demonstrated the formation of new chemical compounds, most probably originated through reactions between products from thiourea dioxide thermal decomposition and some highly polar bitumen molecules. As a result of these reactions, which continues even after 60 days, bitumen permanent deformation resistance at high temperature is enhanced, as indicated by a significant increase in its viscosity and elastic features. On the other hand, thiourea dioxide addition produces changes in the bitumen colloidal nature, which improve its flexibility at low in-service temperatures, and consequently its resistance to thermal cracking under loading. In fact, dynamic bending tests indicated a remarkable decrease in the value of binder glass transition temperature, which was further corroborated by differential scanning calorimetry. As a conclusion, thiourea dioxide can be seen as a promising modifiying agent, which can extend the in-service temperature range at which bitumen would present a satisfactory performance.This work is part of a research project sponsored by a MEC-FEDER Programme (Research Project MAT2007-61460) and by a Junta de Andalucía Programme (TEP6689). The authors gratefully acknowledge its financial support. A.A.Cuadri also acknowledges the concession of MEC FPU research fellowship (AP2008-01419).This work is part of a research project sponsored by a MEC - FEDER P rogramme (Research Project MAT2 007 - 61460) and by a Junta de Andaluc í a Programme (TEP6689). The authors gratefully acknowledge its financial support. A.A.Cuadri also acknowledges the concession of MEC FPU research fellowship (AP2008 - 01419).This work is part of a research project sponsored by a MEC-FEDER Programme (Research Project MAT2007-61460) and by a Junta de Andalucia Programme (TEP6689). The authors gratefully acknowledge its financial support. A.A. Cuadri also acknowledges the concession of MEC FPU research fellowship (AP2008-01419)

Potential valorization of waste cooking oils into sustainable bio-lubricants

This work explores the feasibility of using waste cooking oils (WCO) as eco-lubricants. Five WCO from different food facilities were studied. Three of them were fractionated into both lighter and heavier fractions by molecular distillation. A comprehensive chemical characterization (fatty acids distribution, polar compounds and acidity) was carried out on all WCOs and their fractions, which led to set relationships with the oils’ properties (such as viscosity index, low temperature viscous flow behavior, oxidation resistance, etc.). It is worth mentioning the high viscosity index values found in waste cooking oils with both low total polar compounds and acidity level, as well as the benefit which acidity had on their fluidity at low temperature and their lubricity. Moreover, it was also noteworthy that the lighter fractions, merely constituted by free fatty acids (FFA), presented an improved oxidative resistance. The largest OOT enhancement, 12.4%, was found for the light fraction of a non-segregated oil. Moreover, a better thermal stability was shown by the heavier fractions. Finally, both fractions exhibited enhanced friction-reducing capability as compared to their parent WCO. The light fractions from a nonsegregated oil, a fast food restaurant oil and a deep-fried food establishment oil yielded wear reductions of 11.7%, 44.3% and 36.8%, respectively. Therefore, molecular distillation has been proved to be a key strategy to obtain more efficient liquid eco-lubricants.This work explores the feasibility of using waste cooking oils (WCO) as eco-lubricants. Five WCO from different food facilities were studied. Three of them were fractionated into both lighter and heavier fractions by molecular distillation. A comprehensive chemical characterization (fatty acids distribution, polar compounds and acidity) was carried out on all WCOs and their fractions, which led to set relationships with the oils’ properties (such as viscosity index, low temperature viscous flow behavior, oxidation resistance, etc.). It is worth mentioning the high viscosity index values found in waste cooking oils with both low total polar compounds and acidity level, as well as the benefit which acidity had on their fluidity at low temperature and their lubricity. Moreover, it was also noteworthy that the lighter fractions, merely constituted by free fatty acids (FFA), presented an improved oxidative resistance. The largest OOT enhancement, 12.4%, was found for the light fraction of a non-segregated oil. Moreover, a better thermal stability was shown by the heavier fractions. Finally, both fractions exhibited enhanced friction-reducing capability as compared to their parent WCO. The light fractions from a non- segregated oil, a fast food restaurant oil and a deep-fried food establishment oil yielded wear reductions of 11.7%, 44.3% and 36.8%, respectively. Therefore, molecular distillation has been proved to be a key strategy to obtain more efficient liquid eco-lubricants.This work was supported by “Programa Operativo FEDER-Andalucía 2014–2020 from "Consejería de Economía y Conocimiento de la Junta de Andalucía” and the University of Huelva [grant numbers UHU- 1255843 and UHU-202008]. Also, the Social Innovation Chair of “Aguas de Huelva” at the University of Huelva. Funding for open access charge: Universidad de Huelva / CBUA. The authors gratefully acknowledge the recollected waste cooking oil and kindly supplied by the authorized waste manager (GRU 2066) BIOLIA

Bitumen modifiers for reduced temperature asphalts: a comparative analysis between three polymeric and non-polymeric additives

This study presents three bitumen modifiers which may find successful application in the fabrication of binders for warm mix asphalt in the paving industry. In that sense, two non-polymeric additives, thiourea and thiourea dioxide, along with a reactive isocyanate-terminated prepolymer have been evaluated. Viscous flow and linear viscoelasticity tests, at 60 ºC, reveal bituminous modified binders which evolve towards highly viscous materials when subjected to ambient curing. However, at 135 ºC, they show lower viscosity than a typical 3 wt.% SBS binder used as reference. These results suggest modified binders with low viscosity which may contribute to reduce the mix asphalt temperature. On the contrary, they are expected to undergo an important increase in viscosity when the asphalt is in service, which would contribute to improve further their performance. Low temperature performance and effects of short-term and long-term aging were not considered in this study.This work is part of a research project sponsored by a MEC-FEDER Programme of references BES-2008-003572 and AP2008-01419, supported by European Social Fund. The authors gratefully acknowledge its financial support

Preliminary insights into electro-sensitive ecolubricants: A comparative analysis based on nanocelluloses and nanosilicates in castor oil

The newest generation of lubricants needs to adapt to stricter environmental policies. Simple and sustainable formulations with tunable rheological properties under the action of electric potentials may be the key. The present research explored the feasibility of producing electro-sensitive ecolubricants based on nanocellulose (crystalline and fibrillar) or nanoclay (Cloisite 15A montmorillonite and halloysite nanotubes) dispersions in castor oil, at concentrations that ranged from 2 to 6 wt.%. Broadband dielectric spectroscopy (BDS) measurements allowed for a first estimate on the electro-responsive potential of the nanofluids. The nanocelluloses and the montmorillonite suspensions presented a relaxation event in the dielectric loss, e", centered at ca. 2-4 kHz, which is related to interfacial polarization. Moreover, their actual electro-rheological (ER) effect under high electric potentials up to 4 kV/mm was assessed by determining the magnitude of the yield stress from steady flow curves at 25 °C. It was found that the nanocelluloses and the montmorillonite showed an enhancement of three orders of magnitude in their yield stress values at 4 kV/m. This enhancement was much greater than in the halloysite nanoclay, which did not exhibit any polarization). This is the starting point for the development of environmentally friendly ER lubricating fluids, based on nanocellulose and montmorillonites (layered nanosilicates), which might assist in reducing the friction and wear through the application of controlled electric fields.publishersversionpublishe