In reviewing the papers published by the author and his coworkers, the discussion was focused on two topics; entaglements of linear polymers in concentrated solutions and steady-state compliance of branched polymers.
1) The intersegmental interaction working as entanglements in polymer solutions is different in different solvents as well as in different phenomena. The difference can well be observed by determining the critical degree of coil-overlapping in the scaling or its corresponding plot, at which entanglements begin to appear. The entanglement formation was found to become more difficult in the order of osmotic pressure, viscosity and steady-state compliance. And, the hydrodynamic entanglement for viscosity is stronger in poor solvents than in good solvents. Moreover, the shear rate dependences of steady-flow viscosity and steady-state compliance at different polymer concentrations form universal curves if they are reduced by a factor of 1/C². That is, the effect of increasing shear rate is equivalent to that of decreasing polymer concentration. This means that the main effect of increasing shear rate would be in decreasing the effective entanglement density. An analysis of transient viscoelastic phenomena such as stress-overshoot was presented based on this network rupture model. From these experimental results, it was pointed out that the solution viscosity of a linear polymer in poor solvents would be, in general, higher than in good solvents, whereas it is well known to be opposite in dilute solutions.
2) As molecular weight M of a polymer is increased and/or as polymer concentration C is increased, the steady-state compliance J_e of both linear and branched (nearly star-shaped) polymers transfer from the dilute solution region (J_e∝M/C) to the quasi-network region (J_e∝M⁰/C²) at a critical value of CM. In the dilute solution region, J_e of star-shaped polymers is lower than that of the corresponding linear polymers having the same molecular weight, whereas it is opposite in the undiluted state. From comparison between polymer concentration dependences of branched and linear polymers it was pointed out that the critical value of CM for star-shaped polymers is much higher than that for linear polymers, in contrast to the fact that the critical degree of coil-overlapping for viscosity is not much affected by branching. Consequently, J_e of star-shaped polymers becomes higher than that of the corresponding linear polymers at the undiluted state.

View full abstract

This paper gives a review on the rheological properties of polymer melts and concentrated solutions of branched polymers. The molecular weight dependences of various viscoelastic parameters, such as zero-shear viscosity η₀, steady-state compliance J_e⁰, and entanglement compliance J_eN⁰ for star-shaped polymers are described in terms of numbers and molecular weights of branches. Reductions of the molecular weight dependences of η₀ and J_e⁰ have been investigated. The effect of molecular weight between branch points on the viscoleastic behavior for concentrated solutions of randomly branched polymers is described.

View full abstract

Flow behavior in mixing of polymeric materials was investigated using several types of mixers. Low density polyethylene (LDPE) and natural rubber (NR) were employed as typical examples of pelletized plastics and bulky rubbers, respectively. Carbon black (CB) was added to evaluate a performance of mixers. The flow behavior of the materials in the initial stage of mixing, where polymers are converted from solid to fluid, has been observed and analyzed. The mechanisms of the following phenomena have been clarified; i) behavior of unmelted region and generation of a high pressure in LDPE mixing, ii) breaking phenomenon of materials, iii) two low-temperature regions and torque peaks, iv) breaking and granulation processes, and v) mechanical breakdown in NR molecules. An optimum dispersional parameter has been discussed to predict a CB dispersion level. Using this parameter, optimum mechanical dimensions of a mixing rotor were obtained for the best dispersion of CB.

View full abstract

It has been found by earlier investigators that elastomers in an internal mixer circulate around the mixing chamber. This led the authors to develop a model of 3-dimensional flow within a fully filled mixing chamber. However, internal mixers are largely operated under starved / partially filled conditions. To fully understand the behavior of an internal mixer under practical operating conditions and to model these characteristics, we need to know the distribution of rubber. Thus, an experimental study of the distribution of rubber on rotors in an internal mixer at various fill factors is described for different types of non-intermeshing rotors. Rates of circulatory flows around the mixing chamber are also evaluated. The position of the rubber on the rotors correlates with the predicted position of minimum pressure in the fully filled mixer based on an earlier model of flow by the authors. This is used as the basis of a new model to represent flow in a starved internal mixer. This new theory predicts both placement of rubber on the rotors and its rate of circulation around the chamber.

View full abstract

A blending law for linear viscoelasticity of entangled polymer systems is proposed in the present study, based on the extended tube model theory presented by Doi et al. in 1987. The following conclusions are obtained concerning the relaxation processes of entangled chains in binary blend systems where there are entanglements between the chains of higher molecular weight component.
(1) Constraint release due to relaxation of shorter chains in the blends gives rise to the following three changes in and around the long chains: (a) tube renewal, (b) tube dilation or enlargement of the tube diameter, and (c) large scale conformational re-arrangement due to a change in the tube length.
(2) When the tube diameter does not change (no dilation case), large scale conformational rearrangement of the long chains does not occur, because equilibration of the tube length due to the constraint release is not necessary in this case.
(3) Enlargement of the tube diameter and decrease in the tube length due to the constraint release result in the large scale conformational rearrangement of the long chains.
(4) In order to find experimentally a relaxation function associated with the conformational rearrangement, it is necessary to carry out stress relaxation experiments in a restricted regime corresponding to RD box given by the extended tube model theory of Doi et al.

View full abstract

Mechanical properties and bone density (photon absorptiometry method) of bone samples from horses were studied. The dynamic stiffness and tan δ were measured by a viscoelastic spectrometer. The three-point bending test was performed with an Instron-type universal testing machine. A bone densitometer (Norland Instruments) was used for the density measurement. The results are as follows :(1) Three point bending test showed that deformation averaged 5.23 mm, and the fractured load, 22.4 KN. (2) There was a positive correlation between dynamic stiffness and bone density. (3) There was a negative correlation between tan δ and fractured load. (4) There was a positive correlation between Sr content and fractured load. (5) There was a positive correlation between the contents of Ca and P and Vickers hardness number.

View full abstract

The effect of assumed size of dispersoid was investigated by the concentric multi-layer model proposed earlier for simulating the flow of immiscible polymer blend through a tube. The flow curves of PC, SAN and their blends were calculated by changing the diameter (d) of a dispersoid from 0.01 μm to 100 μm. The influence of diameter on calculated results was negligible provided that the diameter was 1 μm (d/2R₁=2×10_-3, R₁; radius of a capillary) or less. The calculated result was not affected by the order of layers, i.e., the matter of which component was in contact with the tube wall, when the assumed particle size was small, and was in good agreement with the observed result.

View full abstract

By using microtip catheter pressure transducers, pressure pulse waves were measured at the aortic arch, the thoracic aorta and the abdominal aorta of WHHL rabbits with inherited hyperlipidemia and premature atherosclerosis. Wave-front velocities at the thoracic and abdominal aortas were higher in WHHL rabbits than in a normal rabbit and increased with advancing age. Pressure pulse waves at each aortic portion showed an increase in amplitude of percussion wave with advancing age, followed by a gradual disappearance of the dicrotic notch and dicrotic wave. The above age-related changes were discussed based on the morphological and rheological features of the atherosclerotic aortic walls.

View full abstract