Controlled composite processing based on off-stoichiometric thiol-epoxy dual-curing systems with sequential heat release (SHR)

Control of curing rate and exothermicity during processing of thermosetting composite materials is essential in order to minimize the formation of internal stresses leading to mechanical and dimensional defects in the samples, especially in thick composite samples. It was recently proposed that sequential heat release, an approach based on the kinetic control of the curing sequence of dual-curing thermosets, would enable a step-wise release of the reaction heat and therefore a better control of conversion and temperature profiles during the crosslinking stage. In this article, it is shown experimental proof of this concept obtained by means of an instrumented mold that can be used for the processing of small samples with and without carbon fiber reinforcement. Safe processing scenarios have been defined by numerical simulation using a simplified two-dimensional heat transfer model and validated experimentally.Peer ReviewedPostprint (author's final draft

Comparison of the nanostructure and mechanical performance of highly exfoliated epoxy-clay nanocomposites prepared by three different protocols

Three different protocols for the preparation of polymer layered silicate nanocomposites based upon a tri-functional epoxy resin, triglycidyl para-amino phenol (TGAP), have been compared in respect of the cure kinetics, the nanostructure and their mechanical properties. The three preparation procedures involve 2 wt% and 5 wt% of organically modified montmorillonite (MMT), and are: isothermal cure at selected temperatures; pre-conditioning of the resin-clay mixture before isothermal cure; incorporation of an initiator of cationic homopolymerisation, a boron tri-fluoride methylamine complex, BF3·MEA, within the clay galleries. It was found that features of the cure kinetics and of the nanostructure correlate with the measured impact strength of the cured nanocomposites, which increases as the degree of exfoliation of the MMT is improved. The best protocol for toughening the TGAP/MMT nanocomposites is by the incorporation of 1 wt% BF3·MEA into the clay galleries of nanocomposites containing 2 wt% MMT.Peer ReviewedPostprint (published version

Laboratory 3.0: manufacturing technologies laboratory virtualization with a student-centred methodology

This paper presents a blended-learning strategy for improving the teaching method applied in the laboratory subject Manufacturing Technologies. The teaching method has been changed from a predominantly teacher-centred to an active learning system with a student-centred focus and e-learning activities. In face-to-face classes, a game-based learning platform has been used. This methodology ensured engaging classes at the same time that provided a useful live feedback for students and teachers. The virtualization of the laboratory was achieved by two different e-learning activities, self-assessment tasks and video clips. These e-learning tools have been used not only to improve the students’ learning but also to enhance their motivation. The results from academic outputs show a significant improvement after the new blended learning method is applied. Moreover, a student satisfaction survey shows the positive impact of the methodology on the students’ engagement and motivationPeer Reviewe

Laboratori 3.0: virtualització del laboratori amb una metodologia centrada en l'estudiant

This paper presents an improvement introduced to a laboratory subject by means of a student - centered blended - learning teaching strategy. The implemented virtual tools (videos and questionnaires) help to prepare the practical sessions and allow the sel f - assessment before and after each practical session. Students have shown a great satisfaction with the method. The analysis of the qualifications obtained has allowed an assessment of the degree of correlation between the different techniques used.Postprint (published version

New epoxy thermosets derived from clove oil prepared by epoxy-amine curing

New thermosets from a triglycidyl eugenol derivative (3EPOEU) as a renewable epoxy monomer were obtained by an epoxy-amine curing process. A commercially-available Jeffamine® and isophorone diamine, both obtained from renewable resources, were used as crosslinking agents, and the materials obtained were compared with those obtained from a standard diglycidylether of bisphenol A (DGEBA). The evolution of the curing process was studied by differential scanning calorimetry and the materials obtained were characterized by means of calorimetry, thermogravimetry, thermodynamomechanical analysis, stress–strain tests and microindentation. 3EPOEU formulations were slightly less reactive, and the thermosets obtained showed higher Tgs than those prepared from DGEBA, since they had higher crosslinking density than formulations with DGEBA because of the more compact structure and higher functionality of the eugenol derivative. 3EPOEU thermosets showed good thermal stability and mechanical properties. The results obtained in this study allow us to conclude that the triglycidyl derivative of eugenol, 3EPOEU, is a safe and environmentally friendly alternative to DGEBA.Postprint (published version

Anàlisi de les qualificacions obtingudes amb una estrategia docent ludificada. Cas pràctic en assignatures de l’àmbit de l’enginyeria mecànica

Es presenta l‘anàlisi de la correlació entre les qualificacions de proves avaluadores tradicionals i les obtingudes amb qüestionaris ludificats. S’ha desenvolupat un mètode per obtenir de forma automatitzada unes qualificacions amb diferents criteris de ponderació (penalització de les respostes incorrectes, segons el temps de resposta i la normalització de les qualificacions). Els resultats mostren correlacions significatives que suggereixen l’ús de les activitats ludificades en l’avaluació sumativa.Peer ReviewedObjectius de Desenvolupament Sostenible::4 - Educació de QualitatPostprint (published version

Hard epoxy thermosets obtained via two sequential epoxy-amine condensations

A new family of dual-curable poly(ß-hydroxyamine ether) thermosets based on amine-epoxy formulations has been prepared and characterized. Both curing stages consist in an epoxy-amine polycondensation, each having different reactivity. Whereas the first one is carried out at relatively low temperature using an aliphatic flexible amine, the second is carried out at high temperature with a rigid aromatic amine. The sequentiality of the curing and the stability of the intermediate materials can be established in the basis of the different nucleophilicity of the amines used. The aromatic amine, with a weakly nucleophilic character, is not able to react with epoxides during the first stage at low temperature. The intermediate and final materials exhibit a wide range of properties, thanks to the different glass transition of both epoxy-amine networks, and can be tuned by changing the relative proportion of both diamines in the formulation. The participation of the epoxy resin in both curing stages ensures the homogeneity of the prepared materials, rendering them excellent candidates for applications such as adhesives or smart materials.Postprint (author's final draft

New BN-epoxy composites obtained by thermal latent cationic curing with enhanced thermal conductivity

A series of boron nitride (BN) composites, with different BN content, were prepared and characterized by cationic curing of DGEBA/BN formulations. As cationic initiator a commercial benzylanilinium salt was used. This cationic system shows good latent characteristics that were not lost on adding the filler. The performance of the catalytic system was optimized by varying the amount of initiator and adding little proportions of glycerol. The kinetics of the curing process was evaluated by calorimetric measurements. The addition of BN allowed increasing thermal conductivity without loss of mechanical properties like Young modulus, impact resistance, adhesion and other thermal characteristics like Tg or thermal stability. In addition, dielectric properties were improved with the increment of filler.Postprint (author's final draft

Structural safety 1994-96 Review and recommendations; eleventh report of SCOSS The Standing Committee on Structural Safety

SIGLEAvailable from British Library Document Supply Centre-DSC:7613.050(11) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Psicothema

Resumen tomado de la publicaciónAntecedentes: la motivación del presente estudio es la baja demanda de la carrera de ingeniería mecánica por parte de los alumnos, y muy especialmente las alumnas, que ingresan en la Universidad. Se planteó que, en parte, esta situación se debía a: (a) un conocimiento erróneo de las tareas propias de la profesión, y (b) una percepción distorsionada y negativa de su entorno y condiciones de trabajo. Método: para evaluar estos dos puntos se desarrollaron dos instrumentos de medida (tareas y percepciones) que se administraron en una muestra de 496 alumnos de Bachillerato. Se utilizó un diseño multi-grupo y los datos se analizaron de acuerdo a un modelo extendido de la teoría de respuesta al ítem. Resultados: en términos generales los resultados apoyan los supuestos de partida. Sin embargo, no se encontraron diferencias significativas entre hombres y mujeres. Discusión: finalmente, se discuten las implicaciones de los resultados cara a futuras acciones de mejora.Universidad de Oviedo. Biblioteca de Psicología; Plaza Feijoo, s/n.; 33003 Oviedo; Tel. +34985104146; Fax +34985104126; [email protected]