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Journal of Thermal Analysis and Calorimetry
Authors: G. Vázquez, J. González-Álvarez, and G. Antorrena

Abstract  

The curing of a phenol–formaldehyde–tannin (PFT) adhesive in the presence of pine or eucalyptus wood has been studied using differential scanning calorimetry. The influence of the adhesive/wood ratio on the activation energy (E a), the temperature of the maximum of the exothermic peak (T p) and the enthalpy of the curing process (ΔH) was analysed. E a, T p and ΔH of the curing reaction decreased when wood was added in the curing system. The adhesive/wood interaction did not depend significantly on wood species.

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Journal of Thermal Analysis and Calorimetry
Authors: G. Vázquez, F. López-Suevos, J. González-Alvarez, and G. Antorrena

Summary  

Phenol-urea-formaldehyde-tannin (PUFT) adhesives have been prepared by copolymerization at room temperature of pine bark tannins with phenol-urea-formaldehyde (PUF) prepolymers prepared under varying operating conditions. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) have been used to analyse the curing of prepolymers and adhesives. DSC curves were obtained at three different heating rates and, by means of the Model Free Kinetics isoconversional method, chemical conversion vs. time at a given temperature was obtained. Mechanical conversion was calculated from DMA storage modulus data for those adhesives which gave the best results for plywood and MDF boards.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Valeria Palermo, Ángel G. Sathicq, Patricia G. Vázquez, Horacio J. Thomas, and Gustavo P. Romanelli

Abstract

In this research, we report the preparation of doped PMo Keggin heteropolyacids where Mo is partially replaced by V, Bi, and Bi–V. These catalysts were characterized by means of ICP-AES analysis, 31P-NMR, UV–visible spectra, FT-IR spectra, thermal analysis, and textural properties. In addition, the activities of the synthesized catalysts were evaluated in the selective oxidation of sulfides to sulfoxides/sulfones. The incorporation of V, Bi and Bi–V into the structure of H3PMo12O40 increases the catalytic activity. The two most active catalysts, those with V and V–Bi were supported on aminopropyl-functionalized silica (SiO2NH2) and they were found to be and efficient heterogeneous catalysts for the selective oxidation of diphenylsulfide to the corresponding sulfoxide/sulfone.

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Acta Alimentaria
Authors: F.J. Vazquez-Armenta, J.F. Ayala-Zavala, G.I. Olivas, F.J. Molina-Corral, and B.A. Silva-Espinoza

This study evaluated the effect of onion essential oil (OEO) (0, 0.5, 2.5, and 5 mg ml−1) on microbial growth, browning decay, and sensorial appealing of cut potatoes stored for 15 days at 4 °C. Dipropyl disulphide and dipropyl trisulphide were the main constituents identified in OEO, and its application at a dose of 0.5 mg mlt-1 was the most effective to prevent browning (38.5% inhibition respect to control) during storage, inhibiting PPO activity (39% respect to control) after the treatment. The higher the added OEO concentration the lower microbial growth of the treated product was, achieving a reduction of 1.27 log CFU g−1 for the 5 mg ml−1 treatment. The odour and flavour appealing of cut potatoes were well received by the panelists after 10 days of storage. Therefore, the use of OEO in cut potatoes has a potential as antimicrobial and antibrowning agent.

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Journal of Thermal Analysis and Calorimetry
Authors: Javier A. Díaz-Ponce, Eugenio A. Flores, Alfonso Lopez-Ortega, Jose G. Hernández-Cortez, Arquimides Estrada, Laura V. Castro, and Flavio Vazquez

Abstract

A simplified equation relating water droplet size distribution to crystallization temperature, determined from differential scanning calorimetry (DSC) curves of aqueous emulsions of petroleum is reported in this article. A series of water-in-oil (W/O) emulsions was prepared by dispersion of water in different Mexican crude oils; in a classical DSC experiment, these emulsions were submitted to a regular heating and cooling cycle within temperatures including freezing and heating of dispersed water. The Z-average diameters of the water drops (D dz) were estimated this way and correlated with petroleum composition.

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