Rheology history

This studies have shown that the rheological parameters are affected by the type of measuring device, composition of the paste and rheological history of the sample. The pastes can be attributed to the Newtonian or non-Newtonian types of liquid between the later the plastic (Bingham), pseudo-plastic or exhibiting the dilatancy phenomena can be differentiated. Moreover, the pastes reveal basically the thixotropy or anti-thixotropy properties. 

This importance has been demonstrated in a variety of ways. First of all, the porosities of the sand or screen pack are quite critical. It has been shown that these can have a definite effect on final fiber properties. Beyond this, even the placement of a given porosity medium (sand or screen) in a layered pack can exert a strong influence on the product properties. Such behavior shows that the rheological history of the melt in the pack is a factor in setting yam properties. 

Both the gross mechanical properties and the absence of thermal expansion effects are intimately associated with all levels of structure within the material. Those structures, themselves, depend on the rheological history of the product and understanding them is central to the commercial development of this class of polymer. 

Object in this section is to review how rheological knowledge combined with laboratory data can be used to predict stresses developed in plastics undergoing strains at different rates and at different temperatures. The procedure of using laboratory experimental data for the prediction of mechanical behavior under a prescribed use condition involves two principles that are familiar to rheologists one is Boltzmann s superposition principle which enables one to utilize basic experimental data such as a stress relaxation modulus in predicting stresses under any strain history the other is the principle of reduced variables which by a temperature-log time shift allows the time scale of such a prediction to be extended substantially beyond the limits of the time scale of the original experiment. 

The rheology of hydroxypropylguar is greatly complicated by the cross-linking reactions with titanium ions. A study to better understand the rheology of the reaction of hydroxypropylguar with titanium chelates and how the rheology depends on the residence time, shear history, and chemical... 

Complex (polymer) fluids can exhibit fascinating rheological properties that depend upon the history of the deformation, rather than the instantaneous state of deformation as in Newtonian fluids. As early as ad 100, the great Roman historian Cornelius Tacitus described the harvest of bitumen near a lake in The Histories V. He wrote [1] ... 

Craigie, L.J. "A New Method for Determining the Rheology of Crosslinked Fracturing Fluids using Shear History Simulation," SPE/DOE paper 11635, 1983 SPE/DOE Symposium on Low Permeability, Denver, March 14-16. 

The time-dependent rheological behavior of liquids and solids in general is described by the classical framework of linear viscoelasticity [10,54], The stress tensor t may be expressed in terms of the relaxation modulus G(t) and the strain history ... 

EFFECT OF THERMAL HISTORY ON THE RHEOLOGICAL BEHAVIOR OF THERMOPLASTIC POLYURETHANES... 

These two mathematical Equations (4.59) and (4.60) illustrate an important feature about linear viscoelastic measurements, i.e. the central role played by the relaxation function and the compliance. These terms can be used to describe the response of a material to any deformation history. If these can be modelled in terms of the chemistry of the system the complete linear rheological response of our material can be obtained. 

Rokudai, M., Mihara, S., and Pujiki, T., Influence of Shearing History on the Rheological Properties and Processability of Branched Polymers. II. Optical Properties of Low-Density Polyethylene Blown Pilms, /. Appl. Polym. Set, 23, 3289 (1979) MaiUefer, C., Screw for Extrusion Apparatus, U. S. Patent 3,358,327 (1967)... 

One of the major difficulties in developing theories of the rheology of coagulated or flocculated dispersions is that the microstructures of the aggregates are nonequilibrium structures under shear. Understandably, the rheology of such dispersions is history dependent, as we have seen above, and requires computer simulations and nonequilibrium statistical mechanics for proper study. 

VISCOELASTICITY. Mechanical behavior of material which exhibits viscous and delayed clastic response to stress in addition to instantaneous elasticity. Such properries can be considered to be associated with rate effects—time derivatives of arbitrary order of both stress and strain appearing in the constitutive equation—or hereditary or memory influences which include the history of the stress and strain variation from the undisturbed state. See also Rheology. 

The rheological behaviour of thermotropic polymers is complex and not yet well understood. It is undoubtedly complicated in some cases by smectic phase formation and by variation in crystallinity arising from differences in thermal history. Such variations in crystallinity may be associated either with the rates of the physical processes of formation or destruction of crystallites, or with chemical redistribution of repeating units to produce non-random sequences. Since both shear history and thermal history affect the measured values of viscosity, and frequently neither is adequately defined, comparison of results between workers and between polymers is at present hazardous. 

Rheology of Curing Thermosets. A curing thermoset polymer has a conversion or cure dependent viscosity that increases as the molecular weight of the reacting polymer increases. For vinyl ester whose curing history is shown in Fig. 2.38 [29], the viscosity behaves as shown in Fig. 2.39 [29],... 

Prud homme, R. K., Constien, V., and Knoll, S. (1989). The effects of shear history on the rheology of hydroxypropyl guar gels. In Polymers in Aqueous Media, Glass, J. E. (Ed.), Advances in Chemistry 223, pp. 90-112. Am. Chem. Soc., Washington, DC. 

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