Authors:E. Araújo, Renata Barbosa, Crislene Morais, L. Soledade, A. Souza, and Moema Vieira
Nanocomposites containing both polyethylene and montmorillonite clay organically modified with four different types of quaternary
ammonium salts were obtained via direct melt intercalation. Thus, the main purpose of this work was to evaluate the effect
of the organoclay on the thermal stability of polyethylene. The organoclays were characterized by XRD, FTIR, DSC and TG. The
polyethylene/organoclay nanocomposites were studied by XRD, TEM, TG, besides an evaluation of their mechanical properties.
The results showed that the salts were incorporated by intercalation between the layers of the organoclay and, apparently
that the nanocomposites were more thermally stable than pure polyethylene.
Authors:E. Araújo, Renata Barbosa, Amanda Oliveira, Crislene Morais, T. deMélo, and A. Souza
Polyethylene/montmorillonite clay nanocomposites were obtained via direct
melt intercalation. The clay was organically modified with four different
types of quaternary ammonium salts. The objective of this work is to study
the use of montmorillonite clay in the production of nanocomposites by means
on rheological, mechanical and crystallization properties of nanocomposites
and to compare to the properties of the matrix and PE/unmodified clay nanocomposites.
In general, the tensile test showed that the yield strength and modulus of
the nanocomposites are close to the pure PE. Apparently, the mixture with
Dodigen salt seems to be more stable than the pure PE and PE/unmodified clay.
Authors:H. Polli, L. Pontes, M. Souza, V. Fernandes Jr, and A. Araujo
The degradation kinetics
of polycarbonate with flame retardant additive was investigated by means of
thermogravimetric analysis. The samples were heated from 30 to 900C in
nitrogen atmosphere, with three different heating rates: 5, 10 and 20C
min–1. The Vyazovkin model-free kinetics
method was applied to calculate the activation energy (Ea)
of the degradation process as a function of conversion and temperature. The
results indicated that the polycarbonate without flame retardant additive
starts to loose mass slightly over 380C and the polycarbonate with flame
retardant additive, slightly over 390C (with heating rate of 5C
min–1). The activation energy for flame retardant
polycarbonate and normal polycarbonate were 190 and 165 kJ mol–1,
Authors:M. Brito, Gabriela Barin, A. Araújo, D. de Sousa, S. Cavalcanti, Ana Lira, and Rogéria Nunes
The aim of this work was to study the effect of Lippia sidoides essential oil (LSEO) on stratum corneum lipids and the permeation of salicylic acid. DSC and FTIR spectroscopy were applied.
LSEO 1% (v/v) significantly enhanced salicylic acid flux through snake skin. According to the DSC curves changes in the transition
temperature of the lipids were observed indicating that LSEO can interact with stratum corneum. The IR spectrum of skin treated
with LSEO showed a decrease in the peak intensity for CH2 stretchings (2920–2850 cm–1) however the peak positions did not alter suggesting the extraction of the lipids.
Authors:Juan A. Araujo Ruiz, Guido van Hooydonk, Raul G. Torricella Morales, and Ricardo Arencibia Jorge
Summary This comparative study covers the period 1988-2003 of the Institute for Scientific Information Databases (ISI-DBs), CD-ROM edition: Science Citation Index (SCI), Social Sciences Citation Index (SSCI) and Arts & Humanities Citation Index (A&HCI) as international databases and from the CubaCiencias (CubaCiencias) as an internal database. The number of articles published in Cuban journals, ISI-DBs, the author associativeness trend, the most important institutions and other indicators are collected. However, it is observed that CubaCiencias and ISI-DBs are not perfectly suitable for a study of the productivity of Cuban authors. It is necessary to properly standardize the author fields. For bibliometric studies, Cuba needs a database not only for the published papers in Cuban journals, but also for all the papers published by Cuban authors.
Authors:J. Santos, I. Santos, M. Conceiçăo, S. Porto, M. Trindade, A. Souza, S. Prasad, V. Fernandes, and A. Araújo
Thermoanalytical, kinetic and rheological parameters of commercial edible oils were evaluated. The thermal decomposition of
the oils occurred in three steps, due to polyunsaturated, monounsaturated and saturated fatty acids decomposition, respectively.
According to the temperature of the beginning of the decomposition, the following stability order was observed: corn (A)>corn>sunflower
(A)>rice>soybean>rapeseed (A)>olive>rapeseed>sunflower (A - artificial antioxidants). Kinetic parameters were obtained using
Coats-Redfern and Madhusudanan methods and presented good correlation. According to the activation energy of the first thermal
decomposition event, obtained of Coats-Redfern' method, the following stability order is proposed: sunflower>corn>rice>soybean>rapeseed>olive.
In relation to rheological properties, a Newtonian behavior was observed and no degradation occurred in the temperature range
Authors:Maria Ribeiro da Silva, N. Araújo, A. Silva, L. da Silva, N. Barros, J. Gonçalves, and M. Ribeiro da Silva
The standard (p0=0.1
MPa) molar enthalpies of formation, at T=298.15
K, in the gaseous phase, for three tetradentate Schiff bases involving a N2O2
(H2salch), N,N’-bis(acetylacetone)cyclohexanediimine (H2acacch)
(H2bzacch), were determined from their enthalpies of
combustion and sublimation, obtained by static bomb calorimetry in oxygen
and by the Knudsen effusion technique, respectively. The results are compared
with identical parameters for related compounds previously studied, resulting
from the condensation of salicylaldehyde or β-diketone with aliphatic
Authors:Paula Nunes, Marília Bezerra, L. Costa, Juliana Cardoso, R. Albuquerque, M. Rodrigues, Gabriela Barin, Francilene da Silva, and A. Araújo
The purpose of this study was to evaluate the physical–chemical properties of collagen (CL) and usnic acid/collagen-based
(UAC) films, using differential thermal analysis (DTA), thermogravimetry (TG/DTG), infrared spectroscopy (FTIR), and scanning
electron microscopy (SEM). Both films were prepared by casting process using polyethylene glycol 1500 (PEG 1500) as plasticizer.
In the spectrum of UAC, similar bands of the usnic acid are observed, indicating that the polymerization (film formation)
did not affect the stability of the drug. Distinctly, DTA curve of UAC did not show an endothermic peak at 201 °C, indicative
that the drug was incorporated into the polymeric system. These results were corroborated by the scanning electron microscopy
(SEM). The TG/DTG curves of UAC presented a different thermal decomposition profile compared to the individual compounds and
CL. These findings suggest the occurrence of molecular dispersion or solubilization of the drug in the collagen film.