Thermal curing of an epoxy-anhydride system modified with hyperbranched poly(ethylene imine)s with different terminal groups

New hyperbranched polymers (HBP) have been synthesized by reaction of a poly(ethylene imine) with phenyl and t-butyl isocyanates. These HBPs have been characterized by 1H-NMR (nuclear magnetic resonance of hydrogen) and Fourier transform infrared spectroscopy. Their influence on the curing and properties of epoxy-anhydride thermosets has been studied by different techniques: differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermogravimetry (TG). The curing kinetics has been studied with DSC. Integral isoconversional method and the S ¿ esta´k–Berggren model have been used to determine the activation energy and the frequency factor. The kinetic parameters are very similar for all the studied systems at the middle stage of the process, but changes are observed at the beginning and at the end of the process when these modifiers are used. The HBPs reduce the glass transition temperature of the cured materials. In addition, from the DMA analysis it can be seen that the HBP modifier obtained from phenyl isocyanate hardly changes the storage modulus, but the obtained ones from t-butyl isocyanate decrease it. TG analysis reveals a decrease in the onset temperature of the degradation process upon addition of the HBPs.Postprint (author's final draft

Curing of off-stoichiometric amine–epoxy thermosets

The kinetics of the epoxy–amine polycondensation and the epoxy homopolymerization in off-stoichiometric epoxy/amine formulations with excess of epoxy groups, and in the presence of an anionic initiator have been investigated. Diglycidyl ether of bisphenol A (DGEBA) and diethylenetriamine (DETA) have been used as epoxy and amine reagents, respectively, and 2-methylimidazole (2MI) has been used as anionic initiator. This study has been carried out using a differential scanning calorimeter (DSC). The thermal–mechanical properties of the partially cured and fully cured materials with and without initiator have been determined by DSC and dynamic-mechanical analysis. First, off-stoichiometric DGEBA/DETA mixtures with excess of DGEBA, with and without 2MI, have been reacted isothermally at low temperatures, where only the epoxy–amine condensation takes place, because the epoxy homopolymerization has a very low curing rate. Afterward, samples containing 2MI have been heated at different heating rates to study the homopolymerization process of the epoxy excess. The kinetics of both processes have been analyzed with an isoconversional method to determine the activation energy, and the Šesták–Berggren equation has been applied to determine the frequency factor and the orders of reaction. In the isothermal curing, amine–epoxy condensation, the activation energy and the frequency factor decrease with increasing degree of conversion, but in the homopolymerization process, both magnitudes increase with the degree of conversion. Results show that the dual-curing character of off-stoichiometric DGEBA/DETA thermosets with 2MI as anionic initiator renders them suitable for multistage curing processes in which the degree of cure and material properties in the intermediate stage can be controlled easily and final material properties can be enhanced.Postprint (author's final draft

Time-temperature-transformation (TTT) diagram of dual-curable epoxy thermosets obtained via two sequential epoxy-amine condensations

A simple and robust strategy to generate time-temperature-transformation (TTT) diagrams for dual-curable thermosets is presented. TTT diagram is built for a dual-curable amine-epoxy formulation. Both curing stages are epoxy-amine polycondensations. Whereas the first stage is carried out at relatively low temperature using a strongly nucleophilic aliphatic amine, the second is carried out at high temperature with a weakly nucleophilic aromatic amine. The good separation between curing stages enabled the individual kinetics analysis of each stage by integral isoconversional procedures. Gelation was determined by thermomechanical analysis; the glass transition temperature - conversion relationship was determined by calorimetry and was used to draw the vitrification line. Gelation and vitrification lines were checked by means of solubility tests and temperature modulated calorimetry. The results presented in the form of a TTT diagram showed the disparate reactivity of both curing stages and a substantial storage stability at the intermediate curing stage. These materials show great potential in applications where processing flexibility and intermediate stability are crucial.Postprint (author's final draft

Curing and thermomechanical properties of off-stoichiometric anhydride-epoxy thermosets

n the present work, we report the preparation and characterization of a new family of thermosets based on off-stoichiometric anhydride–epoxy formulations in the presence of an anionic initiator. Diglycidyl ether of bisphenol A (DGEBA) and hexahydro-4-methylphthalic anhydride (HHMPA) have been used as epoxy and anhydride comonomers, respectively, and 1-methylimidazole (1MI) has been used as anionic initiator. The isothermal curing kinetics and the thermal properties of the stoichiometric and the off-stoichiometric systems have been compared. The kinetics of the isothermal curing has been analyzed by differential scanning calorimetry (DSC) using an isoconversional method and the S ¿esta ´k–Berggren equation to determine the activation energy, the frequency factor and the reaction orders. The materials obtained were characterized by DSC and dynamic mechanical analysis. Gelation during epoxy–anhydride condensation was determined by thermomechanical analysis. At the same curing temperature, the reaction is faster in the system with excess of epoxy groups. However, the glass transition temperatures of the partially cured stoichiometric system are greater. The gelation time of the off-stoichiometric system is shorter than that of the stoichiometric one. The results indicate that the dual-curing character of off-stoichiometric DGEBA/HHMPA thermosets with 1MI as anionic initiator makes them suitable for multistage curing processes with easy control of degree of cure and material properties in the intermediate stage and enhanced ¿nal material properties.Postprint (author's final draft

Hall-Petch strengthening of the constrained metallic binder in WC-Co cemented carbides: Experimental assessment by means of massive nanoindentation and statistical analysis

WC–Co cemented carbides are geometrically complex composites constituted for two interpenetrating networks of the constitutive ceramic and metal phases. Accordingly, assessment of microstructural effects on the local mechanical properties of each phase is a challenging task, especially for the metallic binder. In this work, it is attempted by combining massive nanoindentation, statistical analysis, and implementation of a thin film model for deconvolution of the intrinsic hardness and flow stress of the metallic phase. Plotting of yield stress values as a function of the binder mean free path results in a Hall-Petch strengthening relationship with a slope (ky) of 0.98 MPa m1/2. This value points out the effectiveness of WC–Co phase boundaries as strong obstacles to slip propagation; and thus, for toughening of the brittle phase (WC) by means of crack-bridging ductile (Co) reinforcement.Peer ReviewedPostprint (author's final draft

FIB/FESEM experimental and analytical assessment of R-curve behavior of WC-Co cemented carbides

Exceptional fracture toughness levels exhibited by WC-Co cemented carbides (hardmetals) are due mainly to toughening derived from plastic stretching of crack-bridging ductile enclaves. This takes place due to the development of a multiligament zone at the wake of cracks growing in a stable manner. As a result, hardmetals exhibit crack growth resistance (R-curve) behavior. In this work, the toughening mechanics and mechanisms of these materials are investigated by combining experimental and analytical approaches. Focused Ion Beam technique (FIB) and Field-Emission Scanning Electron Microscopy ( FESEM) are implemented to obtain serial sectioning and imaging of crack-microstructure interaction in cracks arrested after stable extension under monotonic loading. The micrographs obtained provide experimental proof of the developing multiligament zone, including failure micromechanisms within individual bridging ligaments. Analytical assessment of the multiligament zone is then conducted on the basis of experimental information attained from FIB/FESEM images, and a model for the description of R-curve behavior of hardmetals is proposed. It was found that, due to the large stresses supported by the highly constrained and strongly bonded bridging ligaments, WC-Co cemented carbides exhibit quite steep but short R-curve behavior. Relevant strength and reliability attributes exhibited by hardmetals may then be rationalized on the basis of such toughening scenario.Ministerio de España de Economía y Competitividad (Grant MAT2012-34602)Industry-University program between Sandvik Hyperion and Universitat Politècnica de Cataluny

Análisis de patrones en asaltos de espada de alto nivel

El objetivo de este estudio fue la caracterización técnico-táctica de las acciones de combate en asaltos de esgrima de competición, determinando su e&cacia en función del período del asalto en que se realizan, analizando el tiempo efectivo de combate y de pausa, e identi&cando si existen regularidades en las conductas de los esgrimistas en competición. Para ello se utilizó un diseño observacional puntual, nomotético y multidimensional. El instrumento observacional ESGRIMOBS fue validado mediante un panel de expertos compuesto por 17 especialistas. Se utilizó como instrumento de registro el programa LINCE, y los registros obtenidos fueron tratados y recodi&cados a través del programa Microsoft® O;ce Excel® 2013. El análisis estadístico descriptivo e inferencial se realizó mediante el programa PASW Statistics para Windows y el análisis de patrones a través de <eme. La &abilidad en la observación se determinó mediante el grado de concordancia intra e interobservador. Se analizaron 14 asaltos del Campeonato del Mundo de espada masculina de categoría absoluta. El 43,1 % (±13,3) de las acciones analizadas fueron e&caces, apreciándose un claro incremento de la e&cacia en el transcurso del asalto. A medida que avanza el asalto el tiempo efectivo de combate disminuye y se alargan los tiempos de pausa. Se identi&caron 72 T-Patterns que mostraron distintas regularidades en los 14 combates analizados. En conclusión, se dispone de una herramienta válida para el análisis técnico-táctico y de la estructura temporal de asaltos de esgrima, pudiendo con&gurarse la detección de T-Patterns como una nueva estrategia cualitativa en el análisis táctico de la esgrima

Molecular epidemiology of enterovirus 71, coxsackievirus A16 and A6 associated with hand, foot and mouth disease in Spain

Producción CientíficaHand, foot and mouth disease (HFMD) is a childhood illness frequently caused by genotypes belonging to the enterovirus A species, including coxsackievirus (CV)-A16 and enterovirus (EV)-71. Between 2010 and 2012, several outbreaks and sporadic cases of HFMD occurred in different regions of Spain. The objective of the present study was to describe the enterovirus epidemiology associated with HFMD in the country. A total of 80 patients with HFMD or atypical rash were included. Detection and typing of the enteroviruses were performed directly in clinical samples using molecular methods. Enteroviruses were detected in 53 of the patients (66%). CV-A6 was the most frequent genotype, followed by CV-A16 and EV-71, but other minority types were also identified. Interestingly, during almost all of 2010, CV-A16 was the only causative agent of HFMD but by the end of the year and during 2011, CV-A6 became predominant, while CV-A16 was not detected. In 2012, however, both CV-A6 and CV-A16 circulated. EV-71 was associated with HFMD symptoms only in three cases during 2012. All Spanish CV-A6 sequences segregated into one major genetic cluster together with other European and Asian strains isolated between 2008 and 2011, most forming a particular clade. Spanish EV-71 strains belonged to subgenogroup C2, as did most of the European sequences circulated. In conclusion, the recent increase of HFMD cases in Spain and other European countries has been due to a larger incidence of circulating species A enteroviruses, mainly CV-A6 and CV-A16, and the emergence of new genetic variants of these viruses

BioBlitz Serra Llarga-Secans de la Noguera 2021: desenvolupament i espècies presents

En aquest article es fa la descripció de la tasca duta a terme durant el BioBlitz Serra Llarga-Secans de la Noguera dels dies 21 i 22 de maig de 2021 i es presenta el llistat despècies observades amb lobjectiu de facilitar que aquestes observacions es puguin integrar en les bases de dades públiques de biodiversitat.This paper lists the work carried out during the BioBlitz Serra Llarga-Secans de la Noguera on 21-22 May 2021. We present the list of observed species with the aim of facilitating that these observation could be integrated into public biodiversity databases

Los orígenes de la natación en Barcelona, en Madrid y por extensión en España, a través de la figura de Ernesto Masses Forges (1896-1968), un nadador, waterpolista, entrenador, árbitro, organizador, promotor y directivo de la natación Española.

In this work chronicles the history of swimming in Madrid from its origins through the figure Ernesto Masses Forges (1896-1968), a swwimmer, water polo player, coach, referee, organizer, promoter and manager of the Spanish swimming. A person who was involved in the founding of various sports swimming clubs and the corresponding swimming federations at a territorial and state level, convinced of the benefits of swimming as a sport, in all its specialties, a sport to which he dedicated his entire life from his childhood and youth in his native Barcelona to Madrid, where he lived for the rest of his life. A fignter and popularizer of he could, the lack of swimming pools where to practice this sport and in a very special way in Madrid. All this in a historic moment in which there was no tradition, nor facilities, nor swimming clubs in Madrid, being the swimming festivals, the demostrations and competitions, such as the Return to the laKe of the Casa de Campo or the pond of the Retiro, or the Masses or Ulloa Trophies, events that were of great importance in the expansion and diffusion of swimming and other water sports such as water polo or leap jumps.En este trabajo se relata cronológicamente la historia de la natación en Madrid desde sus orígenes a través de la figura Ernesto Masses Forges (1896-1968), un nadador, waterpolista, entrenador, árbitro, organizador, promotor y directivo de la natación española. Una persona que se implicó en la fundación de diversos clubes deportivos de natación y de las correspondientes federaciones denatación a nivel territorial y estatal, convencido de los beneficios de la natación como deporte, en todas sus especialidades, un deporte al que dedicó toda su vida desde su infancia y juventud en su Barcelona natal hasta en Madrid, donde residió el restode su vida. Un luchador y divulgador de la natación, en un mundo aún no globalizado, denunciando siempre que pudo, la falta de piscinas donde practicar este deporte y de manera muy especial en Madrid. Todo ello en un momento histórico en el que en Madrid no había, ni tradición, ni instalaciones, ni clubs de natación, siendo los festivales de natación, las demostraciones y competiciones, como la Vuelta al Lago de la Casa de Campo o al estanque del Retiro, o los Trofeos Masses o Ulloa, unos eventos que tenían gran importancia en la expansión y difusión de la natación y de otros deportes acuáticos como el waterpolo o los saltos de palanca