Different aspects of the rheology of melt spinning are reviewed. These include (i) the behavior of molten polymer filaments during stretching at constant elongation rates, (ii) flow patterns in the entry region of spinnerets, (iii) die swell under applied tension, (iv) spinline dynamics and deformation, (v) crystallization and orientation development in the spinline.
The steady-flow properties of suspensions of powdered glass fibers in polystyrene solutions were measured by means of a coaxial cylinder type rheometer at rates of shear higher than 1 sec<BUP>-1</BUP>. The powdered glass fibers used were short rods in shape. The content of solid particles ranged from 0 to 50wt%. Experimental results reveal that the temperature dependence of steady-flow properties for the suspensions is similar to that for the medium.However, at low rates of shear, the viscosity for suspensions of higher particle contents increased with decreasing rate of shear, indicating that some structure was formed by the solid particles. Double logarithmic plots of the viscosity vs. shear rate for various suspensions were superposable into a master curve by horizontal and vertical shifts over a wide range of the variables, except for the so-called second plateau region. For all the suspensions employed in this study, the horizontal shift factor was equal to the vertical shift factor regardless of the particle content and medium viscosity. This suggests that the increase in relative viscosity of suspensions is due to the increase in relaxation times rather than to the reinforcing effect of the suspended particles. However, the increase in viscosity in the so-called second plateau region could also result from the formation of some internal structure in suspensions.
The effect of solvent on crazing of enameled wires is discussed in the light of rheological data obtained for enameled polymer films. The enamels studied were polyesterimide, modified polyvinyl formal, trimellitic polyamideimide, and Nylon 66. The test wires were specifically prepared by coating these polymers on an oxidized conductor whose adhesion to the polymers was poor, and they were subjected to rheological measurement after treatment by various solvents. Two types of solvent effect were observed on the stress relaxation curves under constant elongation. In one, there was an abrupt change in the stress relaxation rate upon application of the solvent, and in the other, a stress growth for a certain period resulting in a stress relaxation curve with a maximum. This difference seemed to be attributable to the nature of the solvent rather than to the polymer, at least within the tested combinations of polymers and solvents. The mechanical tan curves of the polymer films stripped from wires were also investigated, with and without application of solvents. It has been found that the shift of the glass transition temperature caused by the solvent is a good measure of the solvent effect on crazing of enameled wires. That is, a solvent which lowers more markedly the glass transition temperature of a given polymer film shows a greater tendency to cause crazing.
The ratio of widths R between two phases of a stationary stratified flow for which the phase interface is parallel to the side walls of a rectangular slit is calculated under the condition that the two phases give equal volume fluxes. For a combination of two Newtonian fluids, the width ratio Ris simply proportional to their viscosity ratio. If both components are of the power-law type, R is greater than the viscosity ratio and increases with the amount of shear-thinning (pseudo plasticity) of the higher viscosity component. For a combination of a Bingham fluid with a Newtonian fluid R decreases with increasing yield stress of the former. Measurements of R were made on various combinations of polyvinyl alcohol (PVA) solutions and of suspensions of CaCO3 in PVA solutions. In the former cases, the experimental values were in good agreement with the theoretical values for the power-law fluids. In the latter, R was primarily affected by the yield stress as predicted by the theory, but a correction was found to be necessary for the shear-thinning effect.
This paper deals with the linear viscoelastic relations for transient shear stresses at the start and cessation of steady shear flow. Viscosity growth function η(t) and viscosity decay function η(t) were defined as the limiting values at vanishing rate of shear, of the ratios of shear stresses to the rate of shear at the start and cessation, respectively, of steady shear flow. A short review was given for exact interrelations among η(t), η(t), and other linear viscoelastic functions. Approximation equations for evaluating various functions from the relaxation modulus could be easily transformed into equations for evaluating various functions from η(t). Proposed approximation formulae for complex viscosity and relaxation spectrum proved usable when examined numerically in the cases of wedge- and box-type relaxation spectra. The approximation formulae for the relaxation spectrum may be employed for determining the rate-dependent relaxation spectrum of nonlinear viscoelasticity.
The dilatant behavior of TiO2 (Rutile)-in-water suspensions stabilized with various amounts of sodium pyrophosphate was studied using a caplillary viscometer for a wide variety of solid concentrations, colloidal stabilities, shear histories and capillary dimensions. The onset of dilatancy was observed at lower shear rates, and the extent of dilatancy was found to increase, respectively, with an increase in (a) the solid concentration, (b) the degree of flocculation varied by the dispersing agent (colloidal stability) and the shear stress previously imposed (history of shear), and (c) the length of capillary. In the dilatant region, the apparent viscosity increased not only with increasing shear rate but with shearing time, i. e., resident time of suspension in a capillary at a constant shear rate. Based on these results, it was concluded that the dilatancy observed in this study can be attributed to the progressive flocculation induced by shear. Additionally, there is a discussion of the mechanism of the pseudo-plastic flow observed at the lower and higher shear-rate ends of the dilatant recrion.