Authors:Hellyda K. T. A. Silva, Thiago Chellappa, Fabíola C. Carvalho, Edjane F. B. Silva, Tarcísio A. Nascimento, Antônio S. Araújo, and Valter J. Fernandes Jr.
Biodiesel is defined as a mixture of mono- or di-alquil esters of vegetable oil or animal fats. During long-term storage, oxidation caused by contact with air (autoxidation) presents a legitimate concern in relation to monitoring and maintaining fuel quality. Extensive oxidative degradation may compromise the quality by adversely affecting kinematic viscosity, acid value, or peroxide value. The oxidation susceptibility of biodiesel, due to the presence of triacilglycerides of poly-unsaturated fatty acids, was evaluated in this study. Samples of sunflower, castor, and soybean biodiesels were obtained through the transesterification reaction, with the intention of achieving the thermal stability study through thermogravimetrical analyses and differential scanning calorimetry high pressure. It was furthermore observed through thermogravimetry and pressure differential scanning calorimetry curves that castor biodiesel exhibited the highest thermal and oxidative stability.
Authors:J. R. Azevedo, R. H. Sizilio, M. B. Brito, A. M. B. Costa, M. R. Serafini, A. A. S. Araújo, M. R. V. Santos, A. A. M. Lira, and R. S. Nunes
The purpose of this study was to develop and characterize insulin nanoparticles systems using chitosan. Insulin-loaded nanoparticles were prepared by ionic gelation of chitosan with tripolyphosphate anions (TPP). The interactions between insulin and chitosan were evaluated by differential scanning calorimetry (DSC), thermogravimetry/derivative thermogravimetry (TG/DTG), and Fourier-transform infrared (FTIR) spectroscopy. Besides, particle size distribution, polydispersity index (PDI), zeta potential, and association efficiency (AE%) of the nanoparticles were evaluated. In general, inert nanoparticles and insulin-loaded nanoparticles showed an average size of 260.56 nm (PDI 0.502) and 312.80 nm (PDI 0.481), respectively. Both nanoparticles showed positive charge, but after insulin incorporation the zeta potential was reduced, evidencing its incorporation. Nanoparticles obtained also showed AE% around 70%, measured by high-performance liquid chromatography (HPLC). The results of FTIR, DSC, and TG/DTG corroborated the data presented suggesting that insulin was successfully encapsulated. However, drug incorporation seems to be related not only to electrostatic interactions, but also to physical process and/or adsorption phenomena.
Authors:K. L. G. V. Araújo, P. S. Epaminondas, M. C. D. Silva, A. E. A. de Lima, R. Rosenhaim, A. S. Maia, L. E. B. Soledade, A. L. Souza, I. M. G. Santos, A. G. Souza, and N. Queiroz
Physicochemical and thermal analyses were undertaken to evaluate the influence of the temperature on the oxidation of sea fish oil once its polyunsaturated fatty acids deteriorate rapidly. Fish oil displayed four decomposition steps in synthetic air atmosphere and only one step in nitrogen atmosphere. The first step started at 189 and 222 °C for oxidizing and inert atmospheres, respectively. An OIT value of 53 min was measured at 100 °C. After the degradation process the peroxide index and the iodine index reduced from 35.38 to 9.85 meq × 1000 g−1 and from 139.79 to 120.19 gI2 × 100 g−1, respectively. An increase of the free fatty acids amount from 0.07 to 0.17% was observed while viscosity increased from 57.2 to 58.0 cP. Absorption at 272 nm also increased. The thermogravimetric and spectroscopic techniques are reproducible and versatile being an option for characterization of edible oil oxidation.
Authors:Késia K. V. Castro, Ana A. D. Paulino, Edjane F. B. Silva, Thiago Chellappa, Maria B. D. L. Lago, Valter J. Fernandes Jr., and Antonio S. Araujo
Thermogravimetry (TG) was used in this study to evaluate thermal and catalytic pyrolysis of Atmospheric Petroleum Residue (ATR) which can be found in the state of Rio Grande do Norte/Brazil, after a process of atmospheric distillation of petroleum. The utilized sample in the process of catalytic pyrolysis was Al-MCM-41, a mesoporous material. The procedures for obtaining the thermogravimetric curves were performed in a thermobalance with heating rates of 5, 10, and 20 °C min−1. From TG, the activation energy was determined using the Flynn–Wall kinetic method, which decreased from 161 kJ mol−1, for the pure ATR, to 71 kJ mol−1, in the presence of the Al-MCM-41, showing the efficiency of the catalyst in the pyrolysis of Atmospheric Petroleum Residue.
Authors:Maria J. F. Costa, Antonio S. Araujo, Edjane F. B. Silva, Mirna F. Farias, Valter J. Fernandes Jr., Petrus d’Amorim Santa-Cruz, and José G. A. Pacheco
The nanostructured hybrid AlMCM-41/ZSM-5 composite was synthesized starting from a hydrogel with molar composition SiO2:0.32Na2O:0.03Al2O3:0.20TPABr:0.16CTMABr:55H2O. The cetyltrimethylammonium bromide (CTMABr) and tetrapropylammonium bromide (TPABr) were used as templates. The above mentioned material presents morphological properties with specific characteristics, such as the surface area of the composite which is approximately half of the surface area of the conventional MCM-41. Another interesting feature is the formation of walls with the double of the density of the MCM-41 structure, which characterizes the hybrid material, resulting in a high stability material for catalytic application. The aim of this study is obtain optimized structures of the hybrid material and for this purpose variations in the synthesis time were carried out. A comparative analysis was performed including X-ray diffraction, Fourier transform infrared spectroscopy, and Thermogravimetry measurements. The model-free kinetic algorithms were applied in order to determinate conversion and apparent activation energy of the decomposition of the CTMA+ and TPA+ species from the hybrid AlMCM-41/ZSM-5.
Authors:P. S. Epaminondas, K. L. G. V. Araújo, A. Lima de Souza, M. C. D. Silva, N. Queiroz, A. L. Souza, L. E. B. Soledade, I. M. G. Santos, and A. G. Souza
Chemical and thermal analyses of golden and brown flaxseeds were carried out for raw and toasted seeds aiming at evaluating their nutritional and thermo-oxidative properties. Moisture, lipids, protein, soluble carbohydrates, and ash contents were quantified. Concerning lipids and proteins, in average, no meaningful differences were observed for the two varieties, being also equivalent to the literature data. The golden variety had a lower amount of fibers and a higher amount of soluble carbohydrates than the brown variety. The techniques of thermogravimetry and differential scanning calorimetry were applied for elucidating the thermal degradation process of the seeds. The toasted gold and brown seeds were more stable to thermal decomposition than the raw seeds, under oxidative conditions. Golden seeds seem to be more susceptible to oxidation than brown seeds, under toasting conditions. Finally, no meaningful advantages were observed for the golden seeds in comparison to the brown ones.
Authors:P. S. Epaminondas, K. L. G. V. Araújo, J. A. Nascimento, M. C. D. Silva, R. Rosenhaim, L. E. B. Soledade, N. Queiroz, A. L. Souza, I. M. G. Santos, and A. G. Souza
Physico-chemical properties, spectroscopy, and thermal analyses were used aiming at evaluating the influence of toasting and of the flaxseed variety on thermo-oxidative behavior of flaxseed oils. Thermogravimetry (TG) and differential scanning calorimetry (DSC) were associated to gas chromatography, infrared spectroscopy and UV–Vis spectroscopy, as well as to physico-chemical analyses to characterize the oils obtained from raw and toasted flaxseeds. No meaningful differences in the thermal and oxidative stabilities were noticed comparing oils obtained from the brown and the golden flaxseeds. Nevertheless, the UV–Vis spectra indicated that both flaxseed oils were at the beginning of the oxidation process. The previous toasting of the seeds led to a higher oxidation for both varieties being harmful to the flaxseed oil quality.
Authors:Ellen Denise P. Almeida, Adjane A. Costa, Mairim R. Serafini, Fábia C. Rossetti, Juliana M. Marchetti, Victor Hugo V. Sarmento, Rogéria de S. Nunes, Mário Ernesto G. Valerio, Adriano A.S. Araújo, and Ana Amélia M. Lira
Solid lipid nanoparticles (SLN) without drug and SLN loaded with chloroaluminum phthalocyanine (AlClPc) were prepared by solvent diffusion method in aqueous system and characterized by thermal analyses and X-ray diffraction (XRD) in this study. Determination of particle size, zeta potential (ZP), and encapsulation efficiency were also evaluated. SLN containing AlClPc of nanometer size with high encapsulation efficiency and ZP were obtained. The results indicated that the size of SLN loaded with AlClPc is larger than that of the inert particle, but ZP is not changed significantly with incorporation of the drug. In differential scanning calorimetry (DSC) curves, it was observed that the melting point of stearic acid (SA) isolated and in SLN occurred at 55 and 64 °C, respectively, suggesting the presence of different polymorphs. DSC also shows that the crystallinity state of SLN was much less than that of SA isolated. The incorporation of drug in SLN may have been favored by this lower crystallinity degree of the samples. XRD techniques corroborated with the thermal analytic techniques, suggesting the polymorphic modifications of stearic acid.
Authors:M. R. Serafini, P. P. Menezes, L. P. Costa, C. M. Lima, L. J. Quintans Jr, J. C. Cardoso, J. R. Matos, J. L. Soares-Sobrinho, S. Grangeiro Jr, P. S. Nunes, L. R. Bonjadim, and A. A. S. Araújo
In this investigation, the study of inclusion complexes formation between p-cymene and β-cyclodextrin using the methods of physical mixture, paste (PC) and slurry (SC), was evaluated. The results of DSC and TG/DTG showed that the products prepared by PC and SC methods were able to incorporate greater amounts of p-cymene, as evidenced by the weight loss of 7.15 and 3.97%, respectively, which occurred between 120 and 270 °C. SEM images showed decreased size of the household, especially in the SC product. The absorption bands in the IR spectrum, characteristic of p-cymene, were also identified in the preparations, indicating the presence of the compound in the complex.