Viscosity mismatch

However, dispersion of high-molecular weight rubbers into the monomeric or prepolymer mixtures of the thermosetting resin matrix is usually difficult due to a viscosity mismatch and a lack of solubility or compatibility. 

Tubular-Blown Film Process. This process is more flexible with regard to the permissible polymer viscosity mismatch, control of film orientation balance in the transverse and machine directions through blow-up ratio, and easy randomization of film-thickness variations. Production rates are limited by flow rates per circumferential length of die (pressure drop) and cooling rates (heat transfer). 

Often polymers are intentionally selected with a mismatch in viscosities to avoid flow instabilities. Viscosity mismatch of a factor of 10 or more may be necessary. Layer nonuniformity expected with the mismatch is compensated by using shaped feedport geometry that is, the layers are introduced into the die nonuniformly so that uneven flow within the die results in a satisfactorily uniform... 

Tubular-blown- film dies are more tolerant of viscosity mismatch because the layers are arranged concentrically, ie, there are no ends. Since streamlines... 

This type of interfacial instability can be reduced or eliminated by increasing skin-layer thickness, increasing die gap, reducing total rate, or decreasing skin-layer polymer viscosity. These methods may be used singly or in combination. These remedies reduce interfacial shear stress, and stable flow results when it is below the critical stress for the polymer system being coextruded. Most often skin-layer polymer viscosity is decreased. In feedblock coextrusion the resultant viscosity mismatch imposed by this remedy can cause variations in layer thickness as discussed earlier. Shaped skin layer feedslots are then used to compensate. 

In plastics, relative viscosity can be defined as the ratio of the viscosity of a concentrate to that of the neat carrier polymer at the same temperature. In this use, relative viscosity predicts relative jetness—defined in the same manner—more accurately than the carbon black loading in a concentrate. A mismatch between masterbatch and letdown viscosities causes incomplete mixing and is the reason that relative jetness can decrease with an increase in relative viscosity [5]. 

To obtain the absolute sound attenuation in the coal slurry, the diffraction loss, the acoustic mismatch loss, the attenuation due to the Teflon window, and the oil coupling must be calculated. Thus, it is difficult to accurately determine the absolute attenuation. In practice, one measures the relative attenuation with respect to a standard. The attenuation of ultrasonic waves in a solid suspension is attributed to three major factors, namely, scattering, viscosity, and thermal effects. Although the presence of particles affects the fluid viscosity and thermal conductivity, the primary source of attenuation may be due to particle scattering. Hence, one may define the relative attenuation of the HYGAS coal slurry by comparing the slurry attenuation with that of the carrier fluid, i.e., the toluene/benzene mixture. This can be expressed by the equation... 

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