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Abstract : Application of Disordered Organic Semiconductor Theory to Low Temperature Curing of Epoxy Resins (3)
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Abstract: The steep autocatalytic feature in a highly accurate DSC study of the heat rate from curing an epoxy resin with piperidine at 27.5 Deg C could not be explained using chemical kinetic power laws usually applied to curing epoxy resin products at higher temperatures. The theory of disordered conjugated organic semiconductors developed in the last decade has been applied to the observed heat rate data. Four heat rate sources have been identified to completely account for the experimental data. Two of the four sources generating 80% of the heat are consistent with mobility change of ion pairs indicating that the low temperature cure follows an organic semiconductor mechanism. It was shown that autocatalysis did not begin until about one fiftieth of the epoxy rings were opened (ignition). After ignition the heat rates of two propagation mechanisms grow exponentially. One charge transport mechanism generates a small heat rate but grows immediately after ignition due to an increase in ion pairs by the dopant (piperidine). The second mechanism appears later but becomes dominant, peaking at 50% completion, where the heat rate is about 50 times higher than the start of the first mechanism. The rate increase is attributed to localized energy sites that lower the LUMO level closer to the HOMO level of the monomer increasing the mobility (heat rate). Keywords: Epoxy resins, kinetics (polym), calorimetry, diffusion, organic semiconductors.Download Full Article |
Abstract : Bisphenol, Diethylstilbestrol, Polycarbonate and the Thermomechanical Properties of Epoxy–Silica Nanostructured Composites
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Abstract: The report has a double character: it deals with the synthesis and preparation of a series of polymers based on bisphenol-A (BPA) monomer; a series of physical and thermomechanical properties are examined for one type (diglycidyl ether of BPA, DGEBA with nanosilica) of the prepared materials. The reactions involved in diepoxy curing with a diamine, functional group modelling for cross-linked polymers, formation of a polymer DGEBA, BPA polyaddition to DGEBA forming a polyether, DGEBA curing with Jeffamine and cross-linking to form a resin are analyzed. Nanocomposites of silica, coated with cross-linked epoxy–amine, are synthesized and examined by 29Si-magic-angle-spinning nuclear magnetic resonance and Fourier-transform infrared spectroscopies, thermogravimetric and dynamic mechanical analyses, differential scanning calorimetry and scanning electron microscopy. Epoxy matrix is filled with nanosilica to design materials with defined properties. A low weight percentage of filler results in matrix improvement. Keywords: Polycarbonate, polymer, nanocomposite, nanosphere, nanosilica, amine, nanostructure, nanomaterial.Download Full Article |
Abstract : Electromagnetic Modeling of Dielectric Mixtures
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Abstract: Electromagnetic modeling of dielectric materials allows us to study the effects of electromagnetic wave propagation and how such electromagnetic fields influence and interact with them. Dielectric materials are composites or mixtures, which often are made up of at least two constituents or phases. Modelling the electromagnetic behaviour of dielectric mixtures is crucial to understand how geometrical factors (shape and concentration), electromagnetic properties of inclusions and background medium, influence the permittivity of the overall material. The aim of this work is to develop new analytical models for dielectric mixtures, in order to describe their electromagnetic behaviour and design them with desired electromagnetic properties, for specific required applications. In particular, in this paper a new general expression for the effective permittivity of dielectric mixture is presented. The mixtures consist of inclusions, with arbitrary shapes, embedded in a surrounding dielectric environment. We consider the hosting environment and the hosted material as real dielectrics, both of them as dispersive dielectrics. The proposed analytical models simplify practical design tasks for dielectric mixtures and allow us to understand their physical phenomena and electromagnetic behaviours. Keywords: Analytical models, dielectric mixtures, effective permittivity, dispersive models, polymers.Download Full Article |
Abstract : Mechanical Characterization of Epoxy Polymer Concrete Containing Fly Ash
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Abstract: Polymer concrete is a composite material made of aggregates and polymeric resin as a binder. The applications of polymer concrete is limited not only to the domain of civil engineering but it has got inroads in to structural applications in Machine tool structures. Till date no standard mix design procedures are available for polymer concrete systems. In this research, Polymer concrete samples were made using epoxy resin as a binder, fly ash as a filler and marble waste as aggregate. The various mix proportions were developed using concept of mixture design of experiments. Compressive and flexural strength was evaluated for each composition of polymer concrete thus obtained. The effect of variables such as epoxy resin, fly ash and aggregates were analyzed. An optimum mix composition has been developed using the regression equations. The coefficient of correlation (R-Square) between the experimental value and predicted value was found to be high near about one proving the fitness of the model. Keywords: Polymer concrete, Fly Ash, Mixture design of experiments, Compressive strength, flexural strength.Download Full Article |
