Authors:Manuel Monte, Luís Santos, José Fonseca, and Carlos Sousa
The vapour pressures of six para-substituted benzoic acids were measured using the Knudsen effusion method within the pressure range (0.1–1 Pa) in the following
temperature intervals: 4-hydroxybenzoic acid (365.09–387.28) K; 4-cyanobenzoic acid (355.14–373.28) K; 4-(methylamino)benzoic
acid (359.12–381.29) K; 4-(dimethylamino)benzoic acid (369.29–391.01) K; 4-(acetylamino)benzoic acid (423.10–443.12) K; 4-acetoxybenzoic
acid (351.28–373.27) K. From the temperature dependence of the vapour pressure, the standard molar enthalpy, entropy and Gibbs
energy of sublimation, at the temperature 298.15 K, were derived for each of the studied compounds using estimated values
of the heat capacity differences between the gaseous and the crystalline phases. Equations for estimating the vapour pressure
of para substituted benzoic acids at the temperature of 298.15 K are proposed.
Authors:Maria da Fonseca, Ramon Almeida, Albaneide Wanderley, Ulysses Ferreira, Luiza Arakaki, José Simoni, and Claudio Airoldi
Polar n-alkylmonoamines of general formula H3C(CH2)nNH2 (n = 1, 3, 5) interacted with layered silicate vermiculite at the solid/liquid interface. The maximum amount of amine intercalated
(Nf) inside the interlamellar space were 0.62, 0.46, and 0.38 mmol g−1, to give the following order of intercalation ethyl → butyl → hexylamines. The layered vermiculite solid was suspended in
deionized water and calorimetrically titrated with this series of amines, to give favorable thermodynamic data, such as exothermic
enthalpy, negative Gibbs free energy and positive entropy data.
Authors:José Geraldo de P. Espínola, Evandro P. S. Martins, Franklin P. Aguiar, Haryane R. M. Silva, M. G. Fonseca, L. N. H. Arakaki, and Ercules E. S. Teotônio
The complex BiCl3·L (L = 1,10-phenanthroline) was synthesized and characterized by elemental analysis and infrared spectroscopy (IR). Infrared spectroscopy data suggested that the nitrogen atom of the aromatic ring is bonded to the bismuth atom. The kinetic study of thermal degradation was determined by non-isothermal thermogravimetry. Two methods based on integral equation of Coats-Redfern, were necessary for determining the kinetic trip: the fitting method, known as the checking model and an iso-conversional method. The latter gives the activation energy for each degree of conversion and the first, the kinetic model gives activation energy and the pre-exponential factor for thermal decomposition processes that occur through a single simple mechanism. The kinetic parameters, Ea and log A for the heating rates of 5, 10, and 15 min K−1, were determined considering the decomposition model denoted by F0/R1 in the range of degree of conversion between 0.065 and 0.71.
Authors:Juliana Cordeiro Cardoso, Ricardo Luiz C. Albuquerque Jr., Francine Ferreira Padilha, Felipe Oliveira Bittencourt, Osvaldo de Freitas, Paula Santos Nunes, Newton L. Pereira, Maria José Vieira Fonseca, and Adriano Antunes S. Araújo
The use of biodegradable natural polymers has increased due to the over-solid packaging waste. In this study, a chemical modification of the casein molecule was performed by Maillard reaction, and the modified polymer was evaluated by polyacrylamide gel electrophoresis (PAGE), thermogravimetry/derivative thermogravimetry (TG/DTG), FT-IR, and 1H-NMR spectroscopy. Subsequently, films based on the modified casein were obtained and characterized by mechanical analysis, water vapor transmission, and erosion behavior. The PAGE results suggested an increase of molecular mass of the modified polymer, and FT-IR spectroscopy data indicated inclusion of C–OH groups into this molecule. The TG/DTG curves of modified casein presented a different thermal decomposition profile compared to the individual compounds. Mechanical tests showed that the chemical modification of the casein molecules provided higher elongation rates (45.5%) to the films, suggesting higher plasticity, than the original molecules (13.4%). The modified casein films presented higher permeability (0.505 ± 0.006 μg/h mm3) than the original polymer (0.387 ± 0.006 μg/h mm3) films at 90% relative humidity (RH). In pH 1.2, modified casein films presented higher erosion rates (32.690 ± 0.692%) than casein films (19.910 ± 2.083%) after 8 h, suggesting an increased sensibility for erosion of the modified casein films in acid environment. In water (pH 7.0), the films erosion profiles were similar. Those findings indicate that the modification of molecule by Maillard reaction provided films more plastic, hydrophilic, and sensitive to erosion in acid environment, suggesting that a new polymer with changed properties was founded.