Polymer reinforcement with nanoparticles

The Polymers and Composites research group belongs to the Materials Science and Engineering and Chemical Engineering Department of the University Carlos III of Madrid, Spain. Its objective is the development and characterization of polymeric materials, focussed in their reinforcement through the dispersion of nanoparticles. Following this method, very small additions of nanoreinforcements usually improve mechanical, electrical and optical properties, as well as the service performance of these materials. The research group is looking for companies interested in applying nanotechnologies to polymers of industrial interest

Refuerzo de polímeros con nanopartículas

El grupo de investigación Polímeros y Composites pertenece al Departamento de Ciencia e Ingeniería de Materiales e Ingeniería Química de la Universidad Carlos III de Madrid. Se dedica al desarrollo y caracterización de materiales poliméricos, centrándose en su refuerzo mediante la dispersión de nanopartículas. Por este método, con adiciones muy pequeñas de nanorrefuerzo se suelen mejorar las propiedades mecánicas, eléctricas y ópticas, así como el comportamiento en servicio de estos materiales. El equipo de investigación busca empresas interesadas en aplicar las nanotecnologías a polímeros de interés industrial

The use of 9-anthroic acid and new amide derivatives to monitorize curing of epoxy resins

Curing of an epoxy resin was studied by steady-state fluorescence and correlationed with IR methods to get more insight on the physical processes occurring during the curing of an epoxy/amine system. We have synthesized and tested a set of 9-anthroic acid (AA) derivatives, that are sensitive to changes in the medium properties. Its fluorescence response is analyzed and compared and it is concluded that N-dibutylanthroic acid amide shows the best performance

Curing of polymer matrix composites. Fluorescence study of dansyl fluorophore labelled to glass fibres and DGEBA-ethyelenediamine epoxy resin

Curing process of diglycidyl ether of bisphenol A/ethylenediamine mixture in the presence of glass fibers was monitored by fluorescence in two ways: first, using dansyl labeled glass fibers and diglycidyl ether of bisphenol A (DGEBA)/ethylenediamine mixture and second, using unlabeled glass fibers and DGBA-dansyl labeled/ethylenediamine mixture. Integral fluorescence intensity was analyzed as a function of time. Results allow comparison between the curing process inside the bulk of the resin and at the glass fiber interface. It was concluded that for the system DGEBA/ethylenediamine the polymer matrix viscosity increases with the curing time faster inside the bulk than at the glass fiber interface.Authors wish to thank CAM (07N/0002/1998) for suppor

Glass transition temperature of low molecular weight poly(3-aminopropyl methyl siloxane). A molecular dynamics study

The average specific volume of the model poly(3-aminopropyl methyl siloxane) as a function of temperature near the glass transition was computed from molecular dynamics simulations. The glass transition temperature was defined as the slop intersection around 210 K, a value similar to that of the experimental result. Globular polymer shaped chains were observed where the chain is closed upon itself. Three amino groups of amino propylene chains were located in the center and the rest of the amino groups were situated outside the main chain. The glass transition temperature of this low molecular weight polymer strongly depends on the binding energies between chains. The intersection of binding energy slopes defines a temperature of 213 K near the glass transition temperature. The most important contributions to the glass transition changes were the electrostatic binding contributions. The Van der Waals contributions in the volume changes were less important. The chain mobility was evaluated by the transition between angles for the states trans, g⁺ and g⁻. The glass transition temperature observed experimentally, 208±2 K, is due to cooperative movements of two different torsion angles, (O–Si) and (Si–C) of the main chain and the lateral chain, respectively, and its rotational mobility. Self-diffusion constant variation for all polymer atoms with the temperature is a probe that the polymer chain cooperative movement had started at temperatures around the glass transition temperature.This work was supported by the CAM through Grant 07N/0002/1998

Fluorescence probe-label methodology for in situ monitoring network forming reactions

The curing of the stoichiometric reaction mixture diglycidyl ether bisphenol A (DGEBA) with N-methylethylenediamine (MEDA) and BEPOX 1268 formulation was monitored by FTIR (in the near IR region) and by fluorescence spectroscopy. 5-Dimethylamino-1-naphthalenesulfonamide derivatives and 4-dialkylamino-4′-nitrostilbene structural units were used as labels and/or probes. It has been proved that hardener in BEPOX 1268 formulation consists of amine containing the primary and secondary amino group. The rate constant for the addition reaction of the secondary amino hydrogen to epoxide is approximately two times larger than that of the primary amino group hydrogen in MEDA and several times (∼seven times) lower in the amine component of BEPOX 1268 formulation. The changes in the integrated fluorescence intensity of the label during the epoxy groups conversion indicate the most important changes in chemical transformations of the reaction mixture, i.e. primary reaction of the secondary amino groups, the gel point (DGEBA–MEDA) and entry of the system to the glassy state (for DGEBA–MEDA and BEPOX 1268). The change in slope of the fluorescence half bandwidth dependence on the epoxy groups conversion indicates the maximum concentration of the secondary amino groups in the reaction mixture (BEPOX 1268). It has been shown that the dependence of the first moment of the emission band vs. epoxy groups conversion can be used to determine the epoxy groups conversion in situ and in real time.The authors would like to thank for funding to the European Commission through the BRITE-EuRam project (no. BE97-4472) and to CAM (projects 07N/0002/98 and 3rd Regional Research Programme)

Reactive compatibilization of epoxy/polyorganosiloxane blends

A new thermoset material based on DGEBA with polyaminosiloxane curing agents is presented. The system shows reaction-induced compatibilization which prevents coalescence of polysiloxane and DGEBA rich domains, leading to gradient structured morphologies. The influence of curing temperature and/or chemical nature of the siloxane on the morphology and surface microhardness were examined. When siloxane is pre-reacted with epoxypropylphenylether (EPPE), a more homogeneous material is obtained. Microhardness profiles on the material are strongly influenced by the extension of the compositional gradients

Development of Cocontinuous Morphologies in Initially Heterogeneous Thermosets Blended with Poly(methyl methacrylate)

Morphology and phase separation process in blends of a network-forming reactive polymer, poly(aminopropylmethylsiloxane) (PAMS), in a poly(methyl methacrylate) (PMMA)-modified epoxy system were studied using optical, epifluorescence and scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), and dynamic mechanical thermal analysis (DMTA). The thermoset system was bisphenol A diglycidyl ether (DGEBA) with different PMMA percentages, 2−10% w/w. Phase separation and reaction advancement were monitored in situ. At the concentration studied, PMMA does not influence the kinetics of the curing process, but it strongly affects the reactive compatibilization between DGEBA and PAMS. The morphology obtained consists of a continuous thermoplastic-rich phase surrounding thermosetting connected polyhedral particles of 5−15 μm. This cocontinuous morphology is observed independently of the percentage of PMMA. Results show that the morphology is strongly influenced by the diffusion and viscosity conditions during reactive compatibilization and phase separation. An increase in PMMA content leads to a decrease in the thermosetting polyhedral particle size. In contrast, an increase in curing temperature leads to bigger sizes. The addition of thermoplastic polymers to initially nonhomogeneous reactive blends is a potential route for generating cocontinuous morphologies irrespective of the thermoplastic contentThe authors would like to ex-press their gratitude to the Epoxsil (MAT2000-0391-P4-02) and Fibrodont (MAT2001-0677-P3) projects for financial support. The authors would also like to thank to Dr. I. Esteban (UNED) for his assistance with the TOM micrographs and to Dr. J. Iruin (UPV) for his assistance with the density measurements

Curing of linear and crosslinked epoxy systems: A fluorescence study with dansyl derivatives

The curing of diglycidyl ether of bisphenol A (DGEBA) with N,N′-dimethylethylenediamine (N,N′-DMEDA) or ethylenediamine (EDA) was monitored by fluorescence spectroscopy and Fourier transform infrared (in the near-infrared region). 5-Dimethylamino-naphthalene-1-sulfonamide (DNS) derivatives were used as probes (fluorophores added to the reaction mixture) and labels (fluorophores attached by covalent bonds to diglycidyl reactants). The term containing the ratio of the reaction rate constants for the addition of the secondary and primary amine hydrogens to the epoxide was included in the reduced reaction rate term for the autocatalyzed and catalyzed epoxide curing reactions. The changes in the integrated fluorescence intensities of the labels during the epoxy group conversion indicated, in some cases, the most important changes in the chemical transformations of the reaction mixture: the epoxy group conversion, during which a rapid increase in the tertiary amino group concentration was first observed; the gel point (for EDA); and the entry of the system into the glassy state (for N,N′-DMEDA and EDA). The fluorescence probes monitored neither the gel point nor the threshold of the glassy state. For the DGEBA–N,N′-DMEDA system, a wavy dependence of the integrated fluorescence intensities of the DNS labels on the epoxy group conversion might reflect the molar concentrations of polymer homologues (referred to the initial number of moles in the system) in the reaction mixtures of the diepoxide and secondary diamine.The authors thank the anonymous reviewers for their constructive comments and the European Commission for funding through the BRITE-EuRam project (BE97-4472) and Comunidad Autónoma de Madrid (CAM) (07N/0002/98)

Monitoring of curing process by fluorescence technique. Fluorescence probe and label based on 5-dimethylaminonaphthalene-1-sulfonamide derivatives (DNS)

The curing reaction of glycidyl ether bisphenol A (DGEBA) with n-butyl amine and/or N-methylethylenediamine was monitored by fluorescence spectroscopy. 5-Dimethylaminonaphthalene-1-sulfonamide (DNS) fluorophore was used as a probe and/or label. Fourier transform infrared (FTIR) analysis revealed that the rate constant for the addition reaction of the primary amino group hydrogen of n-butylamine to the epoxide ring is more than four times larger than that arising from a secondary amine. Significant differences have been observed between the fluorescence behavior of the DNS as a probe and label, especially in the system DGEBA-N-butyl amine. Integrated fluorescence intensity for the DNS label, in contrast to the DNS probe, indicates the most important changes in chemical transformations of this reaction mixture (the onset of tertiary amino groups and maximum concentration of secondary amino groups). Similarly, the dependence of the half-bandwidth on the epoxy groups conversion for the DNS label shows these stages of the curing reaction as well. In the system DGEBA-N-methylethylenediamine, the reactivity of the secondary amino group hydrogen is higher than that of the primary amino group. A change in slope of the dependence of integrated fluorescence intensity on epoxy group conversion clearly indicates the gel point and entry of the system into the glassy state. The DNS probe does not sense any of these changes. From the emission spectra of the DNS probe and/or label, the average value = SigmaIF(nu)nu/SigmaIF(nu) of the emission band position has been correlated with the epoxy group conversion determined by FTIR. Smooth dependencies were obtained in all cases. This enables one to monitor on line and in real time the epoxy group conversion.We would like to thank the European Commission for funding through the BRITE-EuRam Project (BE97-4472) and to CAM (07N/0002/98)