Search Results

You are looking at 41 - 50 of 160 items for :

  • "rheological properties" x
  • All content x
Clear All

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.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: J. Santos, I. Santos, M. Conceiçăo, S. Porto, M. Trindade, A. Souza, S. Prasad, V. Fernandes, and A. Araújo

Abstract  

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 studied.

Restricted access

Abstract  

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.

Restricted access

Árkovics E., Keszler J. Friction curve and rheological properties of Ajka red mud (in Hungarian) Metallurgy , Vol. 106, No. 3, 1973, pp. 135–138. Keszler J. Friction curve and

Restricted access

Dello Staffolo, M., Bertola, N., Martino, M. & Bevilaqcua, A. (2004): Influence of dietary fiber and rheological properties of yogurt. Int. Dairy J. , 14 , 263–268. Bevilaqcua A

Restricted access
Acta Alimentaria
Authors: N. Nedić Tiban, V. Piližota, D. Šubarić, D. Miličević, and M. Kopjar

525 532 Marcotte, M., Hoshahili, A. R. T. & Ramaswamy, H. S. (2001): Rheological properties of selected hydrocolloids as a function of concentration and temperature. Fd Res

Restricted access

Abstract  

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.

Restricted access

This study is a multivariate discriminant analysis that was performed to identify a set of physiological characteristics that can be used to distinguish between groups of durum wheat genotypes differing for adaptation to semi-arid environments. To this aim, at first twenty-six genotypes were classified as “adapted”, “nonadapted” or “indeterminate” on the basis of yield and yield stability, as determined in a drought-prone environment of southern Italy, over a minimum of 4 and a maximum of 9 years. Subsequently fifteen morpho-physiological traits and the yields were assessed in a field study. Univariate statistical analysis of morpho-physiological traits to compare genotypes and groups of genotypes showed significant differences between the genotypes, although no single character could be used to discriminate between the genotype groups. On the contrary discriminant functions, based on 13 morpho-physiological traits, were effective for the full discrimination of all of the groups, with a 100% success rate. Four traits was the minimum needed to fully discriminate the “adapted” genotypes. Together with the water status parameter, the rheological properties and the affinity for bound water are new promising leaf traits, to distinguish between the plants coming from these different groups.

Restricted access

Abstract  

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.

Restricted access

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.

Restricted access