Ole Becker

Morphology, thermal relaxations and mechanical properties of layered silicate nanocomposites based upon high-functionality epoxy resins

This paper investigates the possibility of improving the mechanical properties of high-functionality epoxy resins through dispersion of octadecyl ammonium ion-modified layered silicates within the polymer matrix. The different resins used are bifunctional diglycidyl ether of bisphenol-A (DGEBA), trifunctional triglycidyl p-amino phenol (TGAP) and tetrafunctional tetraglycidyldiamino diphenylmethane (TGDDM). All resins are cured with diethyltoluene diamine (DETDA). The morphology of the final, cured material was probed by wide-angle X-ray scattering, as well as optical and atomic force microscopy. The α- and β-relaxation temperatures of the cured systems were determined using dynamic mechanical thermal analysis. It was found that the presence of organoclay steadily decreased both transition temperatures with increasing filler concentration. Further, the effect of different concentrations of the alkyl ammonium-modified layered silicate on the toughness and stiffness of the different epoxy resins was analyzed. All resin systems have shown improvement in both toughness and stiffness of the materials through the incorporation of layered silicates, despite the fact that it is often found that these two properties cannot be simultaneously achieved.

Dielectric relaxation spectroscopy of reactively blended amorphous poly(ethylene terephthalate) -poly(ethylene naphthalate) films

Abstract Reactively blended poly(ethylene terephthalate)–poly(ethylene naphthalate) films of different compositions and degrees of ester exchange reaction have been investigated by dielectric relaxation spectroscopy. The α-relaxation peaks associated with the glass transition have been fitted by the semi-empirical Havriliak–Negami relaxation function to frequency scans. The parameter relating to relaxation broadness, β, and the relaxation strength, Δe, were quantified and were found to be a parameter sensitive to processing conditions. Both values were affected on a molecular level by concentration fluctuation and the molecular chain architecture (such as polymer chain blockiness). Molecular coupling of the blends was determined from the slope of log frequency maxima vs. reduced temperature Tg/T, as commonly done in coupling theory analysis. It was found that the initial materials, PET and PEN show very similar coupling behaviour. Molecular coupling of the blends was little affected by the blend composition or the degree of transesterification. Activation energies of molecular motions have also been determined and show a positive deviation from the rule-of-mixtures averages of the homopolymers which indicates greater chain hindrance to motion of both blocky or the random copolymers formed by the transesterification process.