Viscoelastic properties of poly (vinyl chloride) melts (PVC) were studied with varying the degree of polymerization (P) and some other factors such as plasticizer contents. Effects of copolymerization were also studied by using poly-random-(vinyl chloride-copropylene)(E), poly (vinyl chloride-propylene)-propylene oxide graft copolymer (F) and poly. (vinyl chloride-propylene)-(ethylene-propylene terpolymer) graft copolymer (G) as copolymer samples. Relaxation moduli G (t) of these PVC melts were found to show a very long plateau in the rubbery region and a low slope in the flow region, in contrast to those of other plastics melts like polypropylene. This characteristic of G (t) which is responsible for high viscosity and elasticity of PVC may be related to cross-links caused by crystallites which exist even in molten samples, and it may be an origin of poor processability. For straight PVC samples, G (t) curves were shifted to the side of longer time scale with increasing P. The curves of G (t) for copolymer samples E and F were located in shorter time region than were those of straight samples with equivalent p. In spite of low crystallinity, the G (t) curve of the sample G exhibited a low slope in the flow region, suggesting that a super-molecular cross-linking structure exists in the rubbery phase. As for the effect of plasticizer, the relaxation modulus in the rubbery plateau region reduced and transition to the flow region became gradual with increasing plasticizer content. The activation energy of relaxation decreased with the increase of P for the straight PVC's, and those of the copolymers such as E-, F- and G-samples were considerably lower than that of the straight PVC due to the high mobility of molecular chains.
Based on flow and sedimentation measurements, rheological and dispersing properties of calcite-goethite mixed suspensions were evaluated and their mutual correlation was discussed. By applying Casson's equation to the results of flow measurements, two parameters, as and αβ, were calculated, whereas from sedimentation experiments the median diameter and the sedimentation volume were obtained and taken as the criteria of dispersity. These four parameters varied themselves parallel to each other with varying mixing composition of two solid components, total solid content being kept constant, and they showed maxima at the volume fraction of goethite approximately equal to 0.8. The parameter αβ was found to serve as a practical and yet well defined measure of interparticle forces in liquid media, even for a mixed suspension where heteroflocculation predominantly takes place.
The flow behavior of polymer melts in a “Screw Die” is theoretically analyzed to establish the condition for obtaining the uniformity of extrudate (sheet/film). The isothermal steady flow of incompressible power-law fluids is treated in this study. Polymer melts extruded from an extruder are dragged in the direction of screw channel by the rotation of die screw. Simultaneously, they have a pressure flow through the slit section perpendicular to the screw axis. The analysis is made for two modes of flow, i. e., the screw flow and the die slit flow. The following four cases are studied: i) Modified Newtonian fluids in rectangular channels. ii) Modified Newtonian fluids in rectangular channels having rounded corners. iii) Power law fluids between shallow plate channels. iv) Power law fluids between shallow plate channels including a transverse flow. Die screw is divided into M equal sections along the axis direction. An equation for determining the reduced pressure along the screw can be formulated by a numerical method in above four cases, based on the mass balance in each section between screw and slit flows. An equation for improving the degree of uniformity can be established by utilizing the fact that the relative deviation from the mean flow in the ith section has to be zero for assuring the perfect uniformity. Thus, an iteration method is explored for modifying the dimensions of slit or screw. It is concluded that the zero pressure gradient and the constant die slit dimension is essential for the ideal screw die. This means that the depth of screw channel should decrease linearly with the increase of axial distance.
Nonlinear viscoelastic behavior of rigid poly-vinylchloride (PVC) resin under time dependent extension was investigated at 20°C and 65% R. H. In log modulus-log time plots, the initial modulus decreases and the rate of relaxation increases as the strain increases, and a master curve can be obtained by shifting each of the curves along the log time axis. The master curve.and the shift factors are used as the basic data for constructing singleintegral type constitutive equation of the time-strain reduced model. This equation is applied to predict stress responses under the following tests: (1) two step stress relaxation, (2) loading and unloading at constant strain-rate, and (3) stress relaxation after loading of constant strain-rate. In the two-step stress relaxation, the predicted values are in good agreement with the observed values when the additive strain Δε is positive, while the former are greater than the latter values when Δε is negative. The discrepancy between predicted and observed values of stress becomes more marked as the ratio of |Δε|de to the first strain ε1, increases. In the loading tests at a wide range of constant strain-rates, the ranges of strain where the linear theory is applicable are found to be independent of strain rate. All the results of constant strain-rate experiments can be described by the simple constitutive equation adopted in this study. The applicability of the theory to the results of PVC is better than that to polyethylene studied in our previous papers.
The discharge of powder from a vessel under gravity is often stopped by the formation of bridging. The shape of a vessel exerts a distinguished influence on bridging. It is known that a hyperbolic vessel (whose degree of reduction is uniform in cross sectional area toward the outlet) can avoid irregularities in the discharge and gives a uniform density of the discharged powder. By the pressure distribution in powder, the effect of the shape of a hyperbolic vessel has been studied mathematically, assuming that the curvature of the wall of a vessel or the height of powder is small. It seems that a hyperbolic vessel whose pattern of the pressure distribution is similar to that of a cylindrical vessel has the higher discharge efficiency, and that a conical vessel whose pattern is not similar to that of a cylindrical vessel has the lower one.
The steady flow and dynamic viscoelastic properties of glass beads-polystyrene solution suspensions were investigated using a coaxial cylindrical viscometer. The rheopectic behavior, indicated by remarkable increase of the apparent viscosity with shearing time, was observed. The Casson's equation was applicable to the equilibrium flow response. The second plateau, defined by Onogi et al., appeared at a lower side of the rubbery plateau in the diagram of the absolute value of the complex shear modulus plotted against the frequency, and its appearance was accompanied by a remarkable distortion of a Lissajous' figure from an ellipsoid.
The steady-flow and dynamic properties have been measured by means of a Weissenberg Rheogoniometer for suspensions of relatively small amounts of titanate fibers in a polystyrene solution. The titanate fibers employed in this study were long thin needles, having diameters smaller than 0.5 micron and aspect ratios higher than 40. The results show marked rheopexy when the rate of shear is changed suddenly from a high value to a considerably low value; the shearing stress increases sigmoidally with increasing time and finally reaches an equilibrium value. This behavior can probably be attributed to the formation of such structure as network or skeleton structure of suspended fibers under shear. In the course of the formation of structure, the dynamic storage rigidity G′ increases first and reaches its equilibrium after passing through a maximum, while the loss rigidity G″ shows behavior similar to shearing stress. The frequency dependences of G′ and G″ during the formation of structure in the suspensions are compared with those for several Maxwell type models having different distributions of relaxation times.