Flow characteristics of mixtures of ceramic powder and polymer were investigated with a cone and plate rheometer at high temperatures and at high solid concentrations (40-70 vol%). The ceramic powders were alumina powder and glass beads of various sizes and the polymers were thermoplastic polymers: polypropylene (PP), polyethylene (PE) and polystyrene (PS). The results are as follows:
1) The type of flow changed from Newtonian flow to non-Newtonian flow as the solid concentration increased and the particle size decreased.
2) The viscosity increased with decreasing particle size at a constant concentration of solid.
3) The apparent activation energy of flow evaluated at a constant rate of shear decreased with increasing particle size for the PP- and PS-ceramics systems. For the PE-ceramics system the activation energy was independent of the particle size.

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A new viscoelastic spectrometer for measurements of complex moduli of solid samples in the audiofrequency range from 10² to 10³ Hz was designed based on the mechanical impedance method. The feature of this instrument is to measure mechanical impedance of a rod-shaped specimen at its driving end : one end of the specimen was glued to a mass served as the fixed end; longitudinal vibrations were applied from the other end by an electromechanical driver through an impedance head at various frequencies. The mechanical impedances, forces and accelerations were detected through the impedance head. The measured impedance of the specimen with a dimension comparable to the wavelength was a hyperbolic function of the complex modulus, the dimension, the density of the specimen and the frequency. Here, we used a computer method to seek the particular value of dynamic modulus with which the calculated and observed values of the mecha nical impedance matched with each other. Preliminary tests for this method were demonstrated with poly (vinylidene fluoride), poly (ethylene terephthalates) and plasticised poly (vinyl chloride) samples. For all these samples, the present method gave reasonably good results. The results at low frequencies agreed with the data obtained by conventional Rheovibron.

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Time-dependent viscoelastic properties of a carbon black-linseed oil suspension were investigated using a computer-controlled double cone type rheometer in which the amplitude of applied oscillatory shear could be held constant. Dynamic shear viscosity η′ and rigidity G′ were measured at a frequency of 0.628 rad/sec at relatively small strain amplitudes, 0.5, 1 and 2%. The suspension of carbon black in linseed oil shows a remarkable thixotropic behavior, which is attributable to the change in density of interparticle network structure. The structure seems to change in deformation and to depend on strain amplitude, rate of strain, and strain history. During the structural recovery after cessation of steady shear flow, the values of G′ at strain amplitudes of 1 and 2% reach equilibrium values after attaining maxima. The stress level of the peak values of G′ is close to the yield stress of the system. This phenomenon may be attributable to competition between rupture by oscillation and formation of structural networks. The rupture of the networks increases the internal friction and leads to an increase of viscous component of the system. The kinetics of the formation and the rupture of the interparticle structure can be described by a kinetic equation using structural parameter Q presented by Chaffey. The viscoelastic properties during structure build-up leading to the dynamic equilibrium can be predicted using an empirical kinetic equation that takes into account the kinetic processes of structural networks and the increment of the viscous component due to rupture of the networks. The characteristics in time dependence of the viscoelastic properties at each strain amplitude mainly depend on the rate constant for breaking down of the growing network structure k_t; with increasing strain amplitude, the value of k_t, increases remarkably.

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A simple emprical expression for temperature dependence of liquid viscosity, which carries two adjustable parameters and includes a glass transition temperature, T_g, and the liquid viscosity η_g at T_g, has been proposed in the form :
log(η/η_g)=A[exp{B(T_g-T)/T}-1]
This expression has been applied to 14 liquids including polymeric materials. The mean values of A and B for 11 substances are found to be 15.29±1.04 and 6.47±1.13, respectively. The Andrade equation and the Williams-Landel-Ferry equation for liquid viscosity can be derived analytically from the proposed equation with reasonable approximation.

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The sample of hydroxypropyl cellulose used in this study forms a mesophase at temperatures from about 130°C to about 175°C. The microscopic examination shows that the isotropic phase begins to appear at about 175°C and grows with temperature to become prominent at 190°C. At about 225°C the sample becomes optically isotropic. The DSC curve shows a very broad endothermic area spreading from 130°to 250°C having shallow bottoms at about 175°C and 225°C. The former may be related to the first appearance of isotropic phase and the latter to the transition to the completely isotropic state. In connection with change in state, the steady-flow viscosity decreases with temperature until a minimum is reached at 173°C and then tends to increase to make a peak at 190°C. In the frequency region from 10^-2 to 10² radian·sec^-1, the thermotropic mesophase at 175°C exhibits very; high storage and loss shear moduli of the order of magnitude of 10⁵-10⁶ Pa, in contrast with the magnitude of 10-10³ Pa of the lyotropic mesophase. The logarithmic plot of storage shear modulus against frequency gives a flat curve with a small slope like the plateau zone of rubberlike consistency. The dynamic data of the thermotropic mesophase of hydroxypropyl cellulose at 175°C resemble in dimension the dynamic data at the plateau zone of lightly cross-linked amorphous polymers such as lightly vulcanized Hevea rubber at 25°C. At 211°C the dynamic shear moduli are reduced to one-hundredth of the values at 175°C, indicating that the network is strongly loosened by the preponderance of isotropic phase. At 250°C the dynamic properties change radically and exhibit the characteristics of isotropic liquids. The effect of temperature on the dynamic properties is interpreted in terms of the resistance of network to the oscillatory deformation at different temperatures.

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In order to perform a behavior analysis of polymeric material in a mixer with ovalor wing-type rotors, it was necessary to find a theoretical solution to the movement of an unmelted material layer. This layer, which appeared on to the rotor surface during the initial mixing period, was distinguished from the melt layer by a well-defined boundary. Photographs of material flow during various mixing stages of low-density polyethylene(LDPE) in a single-rotor mixer showed that the umelted layer moved along the rotor surface in the direction away from the tip region and finally broke at the end of the melt pool. This was previously referred to as the “breaking phenomenon.” The motion of the secondary flow boundary point, which is the separation point of the flow from the rotor surface, was analyzed using an assumed temperature distribution for the behavior model. The result agreed well with the actual movement of the unmelted layer. The result of model calculation indicates that the unmelted layer is the secondary flow region at the front face of the oval-type mixer. The breaking causes the undispersed, low-temperature material of the un-melted layer to flow into the melt layer and this gradually passes through the tip region of the rotor. During this passing period, the required torque increased even in the mixing of LDPE. Thus, it became more necessary to determine if this phenomenon corresponds to the second torque peak phenomenon which had been reported by many researchers for polymers containing large quantities of agglomerate particle additives such as carbon black.

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In order to perform behavior and dispersion analyses of polymeric material in an oval- or wing-type mixer, it was necessary to clearify the mechanism on the appearance of the second torque peak during mixing. Experiments were carried out in two stages : 1) mixing of low-density polyethylene (LDPE) by a single-rotor mixer, 2) mixing of LDPE with 40 weight 13% carbon black by a twin-rotor mixer. In the first stage, five thermocouples were attached to the rotor surface, and material temperatures at each point were measured. An unmelted material layer was detected by photographs of material flow and also as appearance of a low-temperature lump in the temperature profiles. The layer moved on the rotor surface up to the end of the melt pool, and it finally broke there. This low-temperature material disseminated into the melt when the breaking occured and then gradually passed through the tip region. The material temperature was thereby lowered in this passing period, resulting in an increase of the required torque. This passing period showed up as an irregular high-torque region which included a second torque peak. Similar analysis in the mixing of LDPE with carbon black in the second experimental stage agreed well with that in the mixing of LDPE. These analyses clarified how the second torque peak appeared. After the passing period the carbon dispersion level became extremely high due to the disappearance of undispersed material and additives. These analyses clarified why the rate of change in such properties as Mooney viscosity, die swelling, resistivity, and dispersion level, suddenly changes at the point of the second torque peak, as reported by many researchers.

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