Effects of a Static Mixer on the capillary flow behavior of high density polyethylene and polystyrene melts were investigated in the temperature region from 150 to 200°C. Two types of dies were employed: The one was a Static Mixer die having 7 elements of 9mm diameter and 12mm length in the reservoir, and the other was an empty-tube die without the Static Mixer in the reservoir. For all test conditions the critical shear rate for spiralling flow increased with the use of the Static Mixer. It was inferred that the increase of the critical shear rate was caused by equalization of temperature in the reservoir due to mixing of polymer melts. The pressure loss induced by the Static Mixer increased with increasing velocity and viscosity. The pressure loss coefficient K, which was introduced by Chen, was 1.73 for the high density polyethylene and 4.70 for the polystyrene.
Transient shear stresses, κη(t, κ) and κη(t, κ), at a sudden start and cessation, respectively, of steady shear flow were measured for a 20% solution of styrene-butadiene-styrene triblock copolymer in cetyl chloride. Here κ is the rate of shear, t the time, η the stress development function, and η the stress decay function. Measurements were performed with a rheometer of the cone-and-plate type in the range 5×10-4<κ<7 sec-1 at 15.8°C and at every 5°C interval starting from 20°C up to 40°C. A polystyrene of molecular weight close to that of polystyrene blocks precipitated from solution when the temperature was decreased below 30°C. Results on η(t, κ) indicated that the contribution from relaxation modes of long relaxation times selectively decreased with increasing rate of shear. The method of reduced variables with respect to κ and the temperature T was not applicable to the steady shear viscosity η(κ) below 30°C. The Cox-Merz empirical law concerning η(κ) and the complex viscosity was not applicable also in the same range of T. These results may be due to destruction of structures formed by precipitated polystyrene blocks in solution below 30°C.
The strain-dependent relaxation modulus G (t, s) was measured for a 20% solution of styrene-butadiene-styrene triblock copolymer in cetyl chloride at 15.8 and 20°C. Measurements were performed with a cone-and-plate relaxometer in the range of shear 0.222≤s≤6.68. The strain-dependent relaxation spectrum H (τ, s) obtained from G (t, s) indicated that the relaxation mode of the longest relaxation time was very sensitive to shear and decreased rapidly in the strain range 0.5<s<1.0. The applicability of the strain-dependent constitutive model (or the BKZ model) was examined: The memory function was obtained from G (t, s) and therefrom were calculated the steady shear viscosity and the transient shear stresses at a sudden start and cessation, respectively, of steady shear flow. Calculated results were in good agreement with the experimental results given in part I.
The development of shearing stress after onset of steady shear flow has been measured for concentrated solutions in chlorinated biphenyl of monodisperse polystyrenes (M=2.75×105 and 1.53×106) and their blends. The effect of molecular weight distribution on the transient behavior has been discussed on the basis of experimental results for solutions of blend and the components. The parameter discussed here is the total strain κ tms at the time tms, when the shear stress takes its maximum. κ is the imposed rate of shear. Rate of shear dependence curves of κ tms measured at various temperatures can be superposed into a master curve. The shift factor is the same as that obtained from the time-temperature superposition of linear viscoelastic functions. For the solutions of monodisperse polystyrene, κ tms is a constant of 2.4, independent of κ, at relatively low rates of shear, and increases monotonically with further increase of κ. On the other hand, the κ dependence curve of κ tms for a blend solution gives a constant value of 3.8 at low rates of shear, and shows the two-step increase with increasing κ. This higher value of κ tms is believed to be related to the higher value of steady-state compliance of the blend sample. It has also been found that each of the above two steps corresponds to each of the components. In the certain range of κ, two overshoot peaks have been observed for stress development curve of a binary blend, whose components have very different molecular weights from each other.
A number of series of W/O-type creams were prepared, in which the oil phase consisted of liquid paraffin and microcrystalline wax. The emulsifying agent employed was polyoxy-ethylene oleyl ether. The dynamic viscoelastic properties of the creams, and also of the oil phases, were measured at 25°C with a Weissenberg rheogoniometer at frequencies ranging from 5×10-3 to 1.582Hz. The frequency dependence of viscoelastic functions was influenced much by the change in the weight fractions of water, but little by the change in the ratio of microcrystalline wax to liquid paraffin. The gradient of curves in logarithmic plots of the viscoelastic functions of the creams against the weight fraction of water changed drastically at a certain weight fraction of water. These results of viscoelastic measurements were compatible with the microscopic appearance of the creams that large particles of microcrystalline wax were dispersed through the liquid paraffin medium, together with emulsified water drops of much smaller size. The observed dependence of the viscoelastic functions on the weight fraction of water was explained qualitatively by the theory of viscoelastic properties of disperse systems proposed by Okano.
The limiting propagation number [Γl*]=[Γl′] i [Γl″] has been calculated for dispersion of elastic spheres in elastic medium in the range of x=kla=10-2 to 102 with varying parameter values of ρ′/ρ, κ′/κ, μ′/κ′and, μ/κ. Here Γl* and Γl are the complex propagation constants of the dispersed system and the medium, respectively, and [Γl*] is defined as -lim _??_ (Γl*-Γl)/Γlc where c is the volume concentration of spheres. κl is the wave number of the longitudinal wave in the medium, a is the radius of sphere, ρ and ρ′are the densities of the medium and the dispersed particles, κ and κ′are their bulk moduli, and μ and μ′are their shear rigidities, respectively. The real component of the limiting propagation number [Γl′]gives a plateau at low values of x, which corresponds to the Rayleigh scattering, and it displays a rather rapid decrease at around x=1 and approaches to zero at higher values of x. The imaginary component [Γl″] displays a maximum at a slightly larger value of x than 1.
The ultrasonic velocity was measured by a sing-around method in bovine erythrocyte ghosts suspended in four mediums with different density ρo and bulk modulus Ko. The limiting numbers of velocity [V] and density [ρ] and the intrinsic bulk modulus [K] were obtained from the concentration dependence of the ultrasonic velocity and the density of the erythrocyte ghost suspensions. The density ρm, the bulk modulus Km. and the hydration δM of the membrane were determined, with the theoretical relation that [ρ]=(1/ρo-1/ρm)(1+δM) and [K]·(Km-K0)(1+δM)/ρmKm.
The carbon fiber composites of thermally stable polymers which have aromatic and/or heterocyclic rings in their main chain were investigated by torsional free oscillation measurement. The composites were composed of two kinds of commercial varnishes, A and B, and four kinds of straight bundles of carbon filaments with different manufacturers, treated (a), non-treated (b), 6,000 filaments (c), and 12,000 filaments (d). The mechanical data were analyzed as Gillham's TBA technique. The results obtained are shown in Figs. 1~4. The relaxations obtained correspond to those observed on film samples.
The rheological properties of TiO2-water suspensions stabilized with sodium pyrophosphate were studied under steady and oscillatory shear using a coaxial cylinder viscometer. The rheopectic behavior resulting from the structual rebuild-up under steady shear was observed. Structual rebuild was also observed under oscillatory shear. When the suspensions were subjected to oscillatory shear of a constant frequency, stress amplitude was found to increase with increasing the time after the shear was applied, and hysteresis loop (Lissajous' figure) gradually deviated from an initial ellipse. The deviation of the hysteresis loop from the ellipse was also observed with increasing strain amplitudes of oscillation. In the case of deviated loop, the absolute value of complex modulus |G*| was calculated as the ratio of the stress amplitude τmax to the strain amplitude γmax. The relation between the-maximum shear_stress τmax=|Gτ*|γmax and the maximum shear rate γmax=ωγmax coincided well with those of shear stress τ and shear rate γ obtained under steady shear.
The dilatant behavior was observed in a high shear rate range for concentrated TiO2-water suspensions stabilized with various amounts of sodium pyrophosphate. The effects of the history of shear, colloidal stability, solid concentration, and capillary length on this behavior were studied using capillary viscometer. The suspension mechanically deflocculated by high shear rate showed the dilatant flow in the shear rate range, where the suspension previously subjected to a low shear rate exhibited a pseudo-plastic nature. The dilatant flow was accompanied by a pseudo-plastic flow at ei ther lower or higher shear rates. In the dilatant region, the flow curve was affected by the length of capillary: The shear rate at the onset of dilatant flow decreased with increasing capillary length. The apparent viscosity increased with increasing average resident time of sample in a capillary. It is concluded that the dilatancy observed in this study was attributable to the dependence of viscosity on shearing time similar to that of rheopexy.