C. Marieta

Characterization of interfacial behaviour in carbon-fibre/cyanate composites

In this study an attempt is made to investigate the influence of surface treatments such as oxidation and sizing on a high-strength carbon fibre in respect of interfacial adhesion in composite materials with a cyanate matrix. For analysing the fibre/resin interfacial adhesion the single-fibre pull-out technique has been used. The interfacial shear strengths obtained by this technique have been compared with results of interlaminar shear strength measurements corresponding to woven composite plates. In order to clarify the nature of this interfacial adhesion, both morphological (by atomic force microscopy, AFM) and chemical characterisation (by Fourier transform infrared, FTIR), have also been carried out.

AFM approach toward understanding morphologies in toughened thermosetting matrices

Atomic force microscopy, AFM, has been used for determining the microstructure of thermosetting matrices toughened by incorporation of core-shell particles and high-performance thermoplastics. A variety of systems has been considered in this work: one group is based on diglycidyl ether of bisphenol-A (DGEBA) epoxy matrix, and the other group is based on bisphenol-A dicyanate (DCBA) matrix. The studied epoxy systems were: DGEBA cured with an aromatic hardener, diamino diphenyl sulfone (DDS), and modified with polymethylmethacrylate (PMMA), or cured with a cycloaliphatic hardener, diamino dimethyl cyclohexylmethane (3DCM), and modified with core-shell particles of polystyrene-co-butylacrylate (PS-co-Bu). The DCBA-based matrices have been modified with polysulfone of bisphenol-A (PSU) or with polyetherimide (PEI). The influence of the modifiers and the curing conditions on the generated morphologies is reported as analysed by AFM in contact and tapping modes.

Effect of the cure temperature on the morphology of a cyanate ester resin modified with a thermoplastic: characterization by atomic force microscopy

A bisphenol A dicyanate (DCBA) resin has been modified with bisphenol-A polysulfone (PSU) at a concentration of 15 wt%. Mixtures, postcured at the same conditions, have been precured at different temperatures. The effect of the curing temperature on the morphology has been studied by Atomic Force Microscopy (AFM). In the present study, we have also compared Scanning Electron Microscopy (SEM) and AFM in order to demonstrate that AFM is a powerful tool for the characterisation of polymer mixtures morphology.

Crystallization of poly(l‐lactid acid) monitored by dielectric relaxation spectroscopy and atomic force microscopy

An investigation was carried out on the crystallization process of poly(l‐lactid acid) by dielectric relaxation spectroscopy and atomic force microscopy. Experimental results were generated by dielectric relaxation spectroscopy over a wide range of frequency and temperature in both the wholly amorphous state and during crystallization. The variation of the average relaxation time was studied during crystallization at 80 °C and the temperature dependence of this relaxation time for wholly amorphous and crystallized samples was analysed. This behaviour was modelled by Havriliak‐Negami and Vogel‐Fulcher equations. The sensitivity of the segmental dynamics to the degree of crystallinity was analysed, taking into account the relaxing segments and the thickness of the amorphous layer between lamellae. The morphologies obtained during crystallization processes at 80, 130 and 150 °C were monitored by atomic force microscopy at both the lamellar level and by analysing the multilayered superstructures formed. Hedrites, intermediate structures between single lamellar crystals and mature spherulites, were found to appear at the highest temperatures, whereas no evidence of hedrites was found at 80 °C, the spherulites seemed to be constructed from a framework of individual dominant lamellae that splay apart and branch. Complementary to the atomic force microscopy study, the evolution of the obtained morphologies was also followed by optical microscopy. Supporting evidence about the thermal behaviour of the polymers was obtained with differential scanning calorimetry.

Effect of Diisocyanate Structure on Thermal Properties and Microstructure of Polyurethanes Based on Polyols Derived from Renewable Resources

Polyols derived from renewables resources are good candidates to obtaining segmented polyurethane elastomers. Diisocyanates with different chemical structure, aliphatic and aromatic, have been used to synthesize by a two step polymerization procedure polyurethane elastomers with different hard segment content. Microphase separation and thermal stability have been studied using attenuated total reflection Fourier transform infrared spectroscopy (ATR‐FTIR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The analysis of the H‐bonded and non H‐bonded urethane carbonyl stretching vibration in the amide I region, the glass transition temperature of the soft and hard segments and the melting temperature and enthalpies of hard segment reveal that aliphatic diisocyanate based polyurethanes present higher phase separation degree and harder segment crystallinity and also superior thermal stability than aromatic diisocyanate‐based polyurethanes.

Properties of a Vinyl Ester Resin Modified with a Liquid Polymer

A vinyl ester (VE) resin was modified with different concentrations of a liquid polymer, polyoxypropylenetriamine (POPTA), in order to study the changes produced during curing and in its final properties. Fourier transform infrared spectroscopy (FTIR) measurements were made to obtain both the styrene and vinyl ester unsaturations conversions during the cure of the resin. The glass transition region was analysed by dynamic mechanical thermal analysis (DMTA), which showed the constancy of glass transition temperature with modifier content. The mechanical properties of the mixtures were also analysed and the results have been related to the flexural behaviour of the cured neat resin.

¿Peligra la escultura del Peine del Viento por la fuerza del oleaje que lo azota? Diseño de un ABP orientado al aprendizaje activo en la formación de Arquitectos Técnicos

In this communication, the design of a PBL, Problem Based Learning, for the teaching of physical and mechanical properties of materials in the subject of Fundamentals of Materials I for a degree in Technical Arquitecture is presented. This new methodology of teaching orientated to the active learning was implemented in the academic course 2012/13. On the basis of the results obtained in the exams, we can confirm that the methodology is suitable and positive for the acquisition of the results of learning proposed for the subject.

Rheokinetic and Dynamic Mechanical Analysis of Tetrafunctional Epoxy/anhydride Mixtures. Influence of Stoichiometry and Cure Conditions

The copolymerization of hexahydrophthalic anhydride (HHPA) with N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) has been studied for several stoichiometric ratios. The rheological, thermal and dynamic mechanical behaviors of these systems were examined. Kinetic studies by differential scanning calorimetry, in both isothermal and dynamic modes, showed a first-order kinetics. Activation energies were also obtained by rheological measurements, through gelation times at different temperatures, with results in agreement with calorimetric results. The dynamic mechanical behavior was studied to analyse the influence of both stoichiometric ratio and cure schedule in the viscoelastic properties of the mixtures.