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San Pablo de la Moraleja, Spain

Gracia-Fernandez C.A.,Thermal Analysis | Gomez-Barreiro S.,University College Dublin | Lopez-Beceiro J.,Polytechnic University of Mozambique | Naya S.,Polytechnic University of Mozambique | Artiaga R.,Polytechnic University of Mozambique
Journal of Materials Research | Year: 2012

Poly(l-lactic acid) (PLLA) is one of the most studied biopolymers nowadays. Due to its good performance, it constitutes an alternative to petrochemical-derived polymers. It was largely studied by differential scanning calorimetry (DSC) and temperature-modulated DSC. Nevertheless, there is an ongoing debate of what happens at the overlapping melting processes. In the present work, the experimental setups are discussed. Different modulation conditions are proposed for the study of the glass transition, cold crystallization, and the two reported melting processes. Finally, the experimental results allowed to measure the heat capacity change at the cold crystallization and a correct interpretation of what happens at the reported double melting peak of PLLA, which involves the existence of three crystalline structures. © Copyright Materials Research Society 2012. Source

Lopez-Paz J.,University of La Coruna | Gracia-Fernandez C.,Thermal Analysis | Gomez-Barreiro S.,University College Dublin | Lopez-Beceiro J.,University of La Coruna | And 2 more authors.
Journal of Materials Research | Year: 2012

Asphalt bitumens are complex colloidal systems of high viscosity and complex behavior, which are mainly used for making asphalt concrete for road surfaces. Thermal and rheological characterizations are needed to understand their complex behavior, particularly at the processing stage. Prediction of properties at short and long observation times is usually performed through time-temperature superposition (TTS) models, which make use of some calculated shift factors. The influence of crystallization-like transformation processes on the validity of these shift factors is investigated here by temperature-modulated differential scanning calorimetry (TMDSC). Four asphalt emulsions are considered in this work, each one with a specific transformation behavior. The structure-properties relationships are explained on the basis of the transformation profiles and rheological data. © Copyright Materials Research Society 2012. Source

Lopez-Beceiro J.,University of La Coruna | Gracia-Fernandez C.,Thermal Analysis | Artiaga R.,University of La Coruna
European Polymer Journal | Year: 2013

A model describing the low temperature solid state phase transformation kinetics observed in a metal organic framework by differential scanning calorimetry (DSC) at several cooling rates is modified so that the reaction rate is now expressed as a function of time and temperature. Thus, when applied to ramp data, the new model exactly matches the former one but, additionally, it allows to explain isothermal data. The new model is tested for primary crystallizations of two polymers from the molten state, using DSC data, cooling ramp experiments at several cooling rates and isothermal experiments. Good fittings were obtained at all the varied experimental conditions with both polymers. The model makes use of three fitting parameters with physical meaning: an upper critical temperature, Tc, an energy barrier, and a reaction-order, n + 1. Additionally, and previously to perform the kinetic fitting, the dependence of the time to the maximum crystallization rate peak on the isothermal temperature was investigated. That dependence was found to follow a simple model which makes use of two parameters related to the limits of the temperature range in which the crystallization may occur. The polymers used in this work were a commercial extruded polyamide and pristine syndiotactic polypropylene. © 2013 Elsevier Ltd. All rights reserved. Source

Pato-Doldan B.,University of La Coruna | Sanchez-Andujar M.,University of La Coruna | Gomez-Aguirre L.C.,University of La Coruna | Yanez-Vilar S.,University of La Coruna | And 6 more authors.
Physical Chemistry Chemical Physics | Year: 2012

We report that the hybrid organic-inorganic compound [(CH3) 2NH2][Mg(HCOO)3] shows a marked dielectric transition around Tt ∼ 270 K, associated to a structural phase transition from SG R3c (centrosymmetric) to Cc (non-centrosymmetric). This is the highest Tt reported so far for a perovskite-like formate that is thus a promising candidate to display electric order very close to room temperature. This journal is © the Owner Societies 2012. Source

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