Authors:J. Santos, L. Lima, Iêda Santos, and A. Souza
The thermal degradation process of mineral base lubricating oils was
studied in this work by means of thermal, spectroscopic and rheologic analysis.
The lubricating oils were degraded at temperatures varying from 150 to 210C,
and for degradation times from 1 to 48 h. After the degradation, the lubricating
oils were characterized by X-ray fluorescence, IR and NMR spectroscopies,
rheological properties and thermal analyses (TG/DSC). The spectroscopic analyses
determined the oxidation reaction products. TG curves indicate that the thermal
stability of lubricating oils is below 161C. TG curves in air present
three mass loss stages, whereas in nitrogen there are only two mass loss steps.
DSC analyses in air indicate two highly exothermic peaks related to hydrocarbon
oxidation and combustion processes, while in nitrogen only two endothermic
peaks were observed. The decrease in the degradation temperature led to a
decrease of the lubricant viscosity.
Authors:L. L. A. Vermeersen, R. Riva, and R. Sabadini
The 3D quasi-static displacements during and following an earthquake provide a wealth of information on the internal structure and rheological properties of the Earth. If an earthquake occurs in a region that has shallow-viscosity zones inside the crust or at the top of the mantle (asthenosphere), then post-seismic displacements of the crust on the order of millimeters per year are possible. These can be detected by means of permanent GPS stations in the years following a faulting event. In this paper we systematically study the influence of viscoelastic simulation model restrictions on co- and post-seismic deformation. Examples include stratification of the Earth model, modeling of the seismic source, influence of compressibility, effects of position and viscosities of shallow low-viscosity layers. It will be shown that some of these model restrictions or assumptions can have non-negligible influences on the simulated 3D co- and post-seismic displacements.
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
In practice, there is a demand for quick characterization of rheological properties of food materials. The exact model calculation requires complex and long-term mathematical process. In this work, a simple, quick linearization method – the Peleg linearization – is discussed and is compared with the Prony series method. In the Peleg linearization only two constants are used, one of them gives the initial rate of relaxation or creep and the second one gives the equilibrium value of relaxing force or of creeping strain. The Prony series approach the relaxation and creep with the sum of two or more exponential functions and equilibrium values. Both methods give the same equilibrium values for both the relaxation and creep of wine gums and apple. The initial increasing rate of creep is higher by the Peleg linearization and lower by the Prony series. At relaxation the initial decreasing rate is lower by the Peleg linearization and higher by the Prony series.
Authors:M. Partini, O. Argenio, I. Coccorullo, and R. Pantani
Aliphatic polyesters are readily degradable polymers, hydrolysis being the dominant mechanism of degradation. On one side,
this makes them extremely interesting for industrial applications in which degradability is required. On the other side, they
present considerable processing problems due to their sensitivity to process and stocking conditions. In this work, the degradation
of two aliphatic polyesters was studied in the molten state by analysing the rheological properties with the aim of defining
the significance of previous thermal history and of residence time at a given temperature. Rheological measurements were adopted
as a mean of analysis for degradation kinetics because rheological properties are strongly dependent on molecular weight.
In particular, the change in complex viscosity (at constant frequency) as a function of time at different temperatures was
measured. The experimental results show that a significant reduction of viscosity takes place during the isothermal tests
for all the materials analyzed. This reduction was ascribed to the hydrolysis reaction. Indeed, a dried sample showed only
a marginal viscosity reduction. After this initial decrease, an increase in viscosity (more pronounced at higher temperatures)
was found for all the materials and at all the temperatures investigated. This phenomenon was ascribed to the inverse reaction
(esterification) taking place in the absence of water. The dried sample showed, in fact, a much faster increase in viscosity
with respect to the undried one. The degradation kinetics was modeled considering both forward and reverse reactions. The
relative rate of the two reactions depends on the moisture content, and thus the water evaporation from the sample was kept
into account in the rate equations.
Authors:M. Bahra, D. Elliott, M. Reading, and R. Ryan
A novel instrument is described called the Thin film Analyser (TFA) which quantitatively measures changes in mechanical and rheological properties of drying films in-situ on a test panel. It is based around a simple force-sensing device, capable of carrying various probes, which can be positioned in anX-Y plane over the panel. Temperature control is achieved by means of a heating block under the sample. By imposing a thermal gradient along the block, measurements can be obtained at a series of temperatures in a single experiment. Several applications of the TFA to the drying of curable and latex-based coatings are discussed, as well as some more specialized uses. The TFA concept represents a novel approach to the thermal analysis of thin films.