Layer-by-Layer Assembly of Efficient Flame Retardant Coatings Based On High Aspect Ratio Graphene Oxide and Chitosan Capable of Preventing Ignition of PU Foam

The layer-by-layer (LbL) technique is adopted for the construction of multilayers encompassing chitosan and graphene oxide (GO) platelets capable of improving the flame retardant properties open cell PU foams. The LbL assembly follows a linear growth regime as evaluated by infrared spectroscopy and yields a multilayer structure where GO platelets are embedded within a chitosan continuous matrix. 3 and 6 bi-layers (BL) can efficiently coat the complex 3D structure of the foam and substantially improve its flame retardant properties. 3BL only add 10% to the original mass and can suppress the melt dripping during flammability and reduce both the peak of heat release rate by 54% and the total smoke released by 59% in forced combustion tests. Unprecedented among other LbL assemblies employed for FR purposes, the deposition 6BL is capable of slowing down the release of combustible volatile to the limits of non-ignitability thus preventing ignition in half of the specimens during cone calorimetry tests. This has been ascribed to the formation of a protective coating where the thermally stable char produced by chitosan serves as a continuous matrix embedding GO platelets, which control volatile release while mechanically sustaining the PU foam structure

Relación de los hongos formadores de micorrizas respecto de las variables fisicoquímicas de suelos de Mendoza cultivados con tomate para industria

Las políticas agrícolas a nivel mundial están tendiendo hacia sistemas agrícolas sostenibles destinados a la producción de cultivos con un mantenimiento del óptimo equilibrio físico, químico y biológico en el suelo. El estudio de diferentes procesos biológicos relacionados a la fertilidad de suelos y nutrición vegetal resulta promisorio para lograr esa armonía. Los beneficios de las micorrizas sobre la nutrición y crecimiento de especies vegetales han sido motivo de estudio desde hace más de medio siglo y aún queda mucho por responder acerca de la interacción entre el ambiente y la nutrición de cultivos hortícolas en zonas áridas regadías. En este trabajo se estudió la presencia de hongos formadores de micorrizas (HFM) en el suelo y el grado de colonización en las raíces de plantas de tomate para industria en relación con variables fisicoquímicas de los suelos. En seis fincas implantadas con Solanum lycopersicum L. (tomate para industria) y cultivadas bajo el protocolo del “Tomate 2000" del INTA, se evaluó abundancia de esporas de HFM en el suelo y porcentaje de micorrizas en la raíz. Además, en el suelo se determinó conductividad eléctrica, pH, textura, nitrógeno total, fósforo extractable, potasio intercambiable y materia orgánica. La abundancia de esporas de los suelos muestreados fue alta respecto de otros suelos agrícolas, mostrando valores entre 2083 y 3858 esporas 100 g-1. El porcentaje de micorrización de las plantas de tomate mostró valores entre 26,45 y 51,55%. No se observó correlación entre número de esporas y porcentaje de micorrización, aunque se vió una tendencia de que a mayor porcentaje de micorrización hubo menor presencia de esporas en el suelo. Respecto a la relación con las variables fisicoquímicas del suelo, se observó que el porcentaje de micorrización estuvo asociado positivamente al contenido de materia orgánica y negativamente al pH y contenido de fósforo edáfico disponible. A medida que aumentó el pH, el contenido de potasio y fósforo edáfico disponible, la abundancia de las esporas se incrementó. Las características fisicoquímicas del suelo afectan de manera diferente la presencia de HFM. En los suelos áridos de la provincia de Mendoza, donde el fósforo tiende a formar compuestos no disponibles para la absorción vegetal y en los cuales el contenido de materia orgánica es generalmente bajo, sería más efectivo y sustentable promover la colonización de HFM en las raíces haciendo un uso racional de la fertilización fosfatada y promover un mayor uso de abonos orgánicos. Esta práctica agrícola, favorecería la simbiosis entre el hongo y la raíz de la planta hospedera, manteniendo, en el caso del cultivo de tomate, un estado nutricional óptimo para la planta.Fil: Carosio, María Emilia. Universidad Nacional de Cuyo. Facultad de Ciencias Agrarias

Three Organic/inorganic Nanolayers on Flexible Foam Allow Retaining Superior Flame Retardancy Performance Upon Mechanical Compression Cycles

The water-based deposition of flame retardant coatings on flexible polyurethane foams has attracted great interest among the scientific community due to the great performances associated with this technology. Unfortunately, this approach results inefficient as it requires a high number of steps in order to achieve the desired properties. In this paper, we report the production of flame-retardant foams by means of the simple deposition of only three nanoparticles containing layers. The composition and order of the deposited layer has been designed in order to provide specific flame retardant actions, targeting the delayed release of polymer decomposition products to the gas phase, the dilution of these flammable products with water, and the intumescent barrier formation. The morphology of the coated foams after the adsorption of each layer has been investigated by scanning electron microscopy, demonstrating the ability of each adsorbed layer to completely wrap the complex 3D structure of the foam. This three layers-based coating produces a protective exoskeleton that is capable of self-extinguishing the flame in standard flammability tests, leaving the foam almost unaffected (final residue 98%). In forced combustion tests by cone calorimetry, treated foams showed considerably reduced combustion rates, with reduced peak of heat release rate (−50%) as well as consistent reduction in the smoke optical density (−51%) and the total smoke release (−34%). In addition, treated foams have been demonstrated to maintain the ability to self-extinguish the flame as well as reduced combustion rates and smoke production even after being subjected to 100 compression cycles

Sobre inestabilidad e integración de tensiones de formulaciones viscoplásticas para hormigón

Se analizan las consecuencias de los postulados de estabilidad en formulaciones elastoplásticas y elasto-viscoplásticas para materiales cohesivo-friccionales. En particular se considera el criterio de inestabilidad en lo pequeño propuesto por Hi116 para sistemas disipativos y sus características espectrales se analizan por medio del Módulo de Rigidez Direccional. Para los fines comparativos de la predicción de inestabilidad en materiales elastoplásticos y viscoplásticos se considera el camino de tensiones seguido en el Ensayo Experimental de Inestabilidad de Smith12. Los resultados muestran la influencia del grado de no asociatividad y del nivel de viscocidad material en la predicción de inestabilidad local.In this work, the consequenses of the stability conditions in elasto-plastic and elastoviscoplastic constitutive formulations for concrete materials are analyzed. In particular, the criterion for local instability by Hi116 is considered and its performance is analyzed by means of the directional stiffness modulus. The numerical results for the stress path of the instability test by Smith12 illustrate the influence of the grade of nonassociativity and of the viscosity in the performance of the instability condition.Peer Reviewe

A DIC based technique to measure the contraction of a skeletal muscle engineered tissue

Tissue engineering is a multidisciplinary science based on the application of engineering approaches to biologic tissue formation. Engineered tissue internal organization represents a key aspect to increase biofunctionality before transplant and, as regarding skeletal muscles, the potential of generating contractile forces is dependent on the internal fiber organization and is reflected by some macroscopic parameters, such as the spontaneous contraction. Here we propose the application of digital image correlation (DIC) as an independent tool for an accurate and noninvasive measurement of engineered muscle tissue spontaneous contraction. To validate the proposed technique we referred to the X-MET, a promising 3-dimensional model of skeletal muscle. The images acquired through a high speed camera were correlated with a custom-made algorithm and the longitudinal strain predictions were employed for measuring the spontaneous contraction. The spontaneous contraction reference values were obtained by studying the force response.The relative error between the spontaneous contraction frequencies computed in both ways was always lower than 0.15%. In conclusion, the use of a DIC based systemallows for an accurate and noninvasive measurement of biological tissues’ spontaneous contraction, in addition to the measurement of tissue strain field on any desired region of interest during electrical stimulation

Tailoring flame-retardancy and strength of papers via layer-by-layer treatment of cellulose fibers

The layer-by-layer (LbL) technology was used to adsorb polyelectrolyte multilayers consisting of cationic polyethylenimine (PEI) and anionic sodium hexametaphosphate (SHMP) onto cellulose fibers in order to enhance the flame-retardancy and tensile strength of paper sheets made from these fibers. The fundamental effect of PEI molecular mass on the build-up of the multilayer film was investigated using model cellulose surfaces and a quartz crystal microbalance technique. The adsorption of a low (LMw) and a high molecular weight (HMw) PEI onto cellulose fibers and carboxymethylated (CM) cellulose fibers was investigated using polyelectrolyte titration. The fibers were consecutively treated with PEI and SHMP to deposit 3.5 bilayers (BL) on the fiber surfaces, and the treated fibers were then used to prepare sheets. In addition, a wet-strength paper sheet was prepared and treated with the same LbL coatings. Thermal gravimetric analysis of LbL-treated fibers showed that the onset temperature for cellulose degradation was lowered and that the amount of residue at 800 °C increased. A horizontal flame test and a vertical flame test were used to evaluate the combustion behavior of the paper sheets. Papers prepared from both cellulose fibers and CM-cellulose fibers treated with HMw-PEI/SHMP LbL-combination self-extinguished in a horizontal configuration despite the rather low amounts of adsorbed polymer which form very thin films (wet thickness of ca. 17 nm). The tensile properties of handsheets showed that 3.5 BL of HMw-PEI and SHMP increased the stress at break by 100% compared to sheets prepared from untreated cellulose fibers

Recent advances in the design of water based-flame retardant coatings for polyester and polyester-cotton blends

Over the last ten years a new trend of research activities regarding the flame retardancy of polymeric materials has arisen. Indeed, the continuous search for new flame retardant systems able to replace the traditional approaches has encouraged alternative solutions, mainly centred on nanotechnology. In this context, the deposition of nanostructured coatings on fabrics appears to be the most appealing and performance suitable approach. To this aim, different strategies can be exploited: from the deposition of a single monolayer consisting of inorganic nanoparticles (single-step adsorption) to the building-up of more complex architectures derived from layer by layer assembly (multi-step adsorption). The present paper aims to review the application of such systems in the field of polyester and polyester-cotton blend fabrics. The results collated by the authors are discussed and compared with those published in the literature on the basis of the different deposition methods adopted. A critical analysis of the advantages and disadvantages exhibited by these approaches is also presented

Formas y representaciones tardías : aproximaciones a una mirada integral al estilo cerámico Sanagasta - Angualasto

El presente trabajo tiene como objetivo brindar los resultados de una primera aproximación al análisis morfométrico y decorativo de un conjunto de vasijas cerámicas de estilo Sanagasta-Angualasto del Período de Desarrollos Regionales (1000 — 1480 AD) del área valliserrana. Las mismas forman parte de colecciones arqueológicas de distintas instituciones académicas y organismos públicos del país, cuyas procedencias en su mayoría corresponden a la provincia de La Rioja, y en menor medida al norte de San Juan y sur-oeste de Catamarca. La perspectiva de la investigaciónse focaliza en comprender los criterios de análisis de forma integral, prestando especial atención a sus mutuas relaciones. De esta manera, los resultados permiten obtener una caracterización detallada de la heterogeneidad de formas de los recipientes cerámicos (cuencos, escudillas, jarras, ollas y tinajas), sus capacidades volumétricas, como también una primera individualización y discriminación de los tipos de motivos y patrones decorativos que constituyen, en conjunto con las formas, dicho estilo.The aim of this work is to offer the results of the first approximation to the morphometric and stylistic analysis of a set of Sangasta-Angualastos s style pottery vessels and pucos from the Regional Developments period (1000 — 1480 AD) of the valliserrana area. These vessels belong to archaeological collections from different academic institutions and public organisms of the country. The origin of most of them is from the province of La Rioja, and in lesser extent the smaller group to the north of San Juan and south of Catamarca. Our perspective is focused on understanding the criteria of integrated analysis, paying particular attention to its mutual relations. Therefore, the results allow to obtain a detailed characterization of the heterogeneity of forms of the different ceramic containers (bowls, jars, pots and vats), their volumetric capacities, as also the first individualization and discrimination of the types of motives and decorative bosses which constitute, as a whole with the forms, the aboye mentioned style.Fil: Revuelta, Claudio. Universidad Nacional de La RiojaFil: Carosio, Sebastián. Universidad Nacional de Cuyo. Facultad de Filosofía y LetrasFil: Aguilar, Juan Pablo. Universidad Nacional de Cuyo. Facultad de Filosofía y Letra