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: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: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.
Thermal, chemical and rheological properties of ultraviolet aged asphalt binder were characterized by differential scanning
calorimetry (DSC), Fourier transform infrared (FTIR) and dynamic shear rheometer (DSR), respectively. Asphalt binder samples
were made with different film thickness (50, 100, 200 and 500 μm) and suffered different ageing time (0, 48, 96 and 144 h),
at a certain UV radiant intensity of 20 w m–2 in a self-made accelerated ageing oven. The results indicate that the UV light ageing would lead to the improvement of thermal
behavior and the growth of the glass transition temperature of asphalt binder. This type of ageing can be also reflected from
the FTIR spectra in terms of the characteristic peaks of the carbonyl groups and sulphoxides. The UV light ageing can change
some rheological parameters of asphalt binder, such as complex modulus and phase angle. The ageing degrees of asphalt binder
by this type of ageing test are mainly related to the ageing time and film thickness of the sample.
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.
Authors:F. Cser, M. Jollands, P. White, and S. Bhattacharya
Cross-linked polymers have particular rheological responses during reprocessing, e. g. if the material is recycled, special
processing conditions are required. Other virgin polymers can be used as a blending component to enhance rheological properties.
Bi-layer film of EVA/LLDPE was produced on a blown film line and cross-linked by high-energy radiation. This film was ‘agglomerated’
then reprocessed in a twin-screw extruder with virgin LLDPE and blown into film. The miscibility of the blend components was
then studied using a TA Instruments temperature modulated differential scanning calorimeter (TMDSC).
It was found that the cross-linked EVA/LLDPE scrap and the LLDPE have a slight miscibility in the liquid state. A bigger portion
of LLDPE was miscible (dissolved) in EVA in low LLDPE blends. A positive deviation in the heat capacity of the LLDPE component
compared to the additivity rule indicated melting to be more reversible in the first heating cycle. This initial miscibility
was attributed to being induced by high shear during processing. A smaller positive deviation also occurred in the second
heating cycle. This was attributed to intrinsic miscibility.