This paper summarizes the results of experiments performed for testing the tube-model theory of Doi and Edwards to describe the nonlinear viscoelasticity of entangled polymeric systems. For each concentrated solution of polystyrene of sharp molecular weight distribution, one can determine a characteristic time constant τA from the shear stress following step-shear deformations of various magnitudes of shear. The Doi-Edwards theory was revealed to describe well various observed rheological phenomena, provided that the time scale of the phenomenon is longer than τA or that the rate of strain is less than τk-1. The experimentally determined quantity τA, being proportional to the square of the number of entanglement per molecule, may give a measure of time in which the fluctuation of the chain contour length equilibrates completely. There are some indications that the concept of tube model is consistent with the phenomena at short times or at high rates of strain, for which the theory for the viscoelasticity has not yet been established.
In order to investigate the effect of relaxation to the stress-strain curves of natural rubber vulcanizates, stress relaxation was measured after the cessation of elongation with various strain rates. Stress relaxation curves obeyed Cotten's equation over a fairly wide time scale. A parameter of Cotten's equation (A) is taken as a measure of the rate of stress decay. It was shown that the relationship between the rate of stress decay and elongation ratio had three distinct regions with respect to elongation ratio, i. e., small, intermediate and large deformations. The ranges of the latter two regions were dependent on temperature, and these regions were indistinguishable at higher temperatures. Density, birefringence and X-ray diffraction measurements revealed that the region of the intermediate deformation was attributable to chain orientation and that the region of the large deformation was attributable to stress induced crystallization.
Monodisperse polyvinylchloride (PVC) spherical particles were prepared by emulsion polymerization. The PVC particles dispersed in the dioctylphtalate have high ζ-potential and form a regular structure of face-centered cubic closed packing. This suspension, in which the crystal-like ordered structure is formed, showed a linear dynamic visco-elastic behavior at low frequencies (0.001Hz~1Hz) under a small strain unless the magnitude of distortion of the particle exceeded the lattice distance. The value of the dynamic rigidity evaluated by experiments at zero frequency limit agreed well with the theoretical value of the static rigidity which was calculated by using modified Hahn-Bross equation. It is suggested that the elastic nature of the crystal-like structure in PVC-suspension is due to an electrostatic potential which is similar to the ionic potential in an ionic crystal. As the speeds or the Brownian motions of the particles and ions become slower by the increase is the medium viscosity, the suspension exhibits stronger elastic properties attributable to the electrostatic potential.
Bending creep tests in the direction perpendicular to grain were carried out on eighteen different wood species during microwave irradiation. When a high power microwave was irradiated on specimens of water-saturated wood, their temperature rapidly rose above the softening temperatures of lignin and hemicellulose and the creep deformation increased markedly with this increase in temperature. Then, the water inside the wood specimens was vaporized, resulting in an anomalous rise in the internal vapor pressure, which drove out the water from the specimens. During such a drying process, the wood specimens showed considerably high plasticity, resulting in large creep deformation. Thus, at the completion of the drying process, considerably large permanent deformation was left. For example, for Hinoki-wood the deformation just before the failure reached more than 30 times the initial, instantaneous deformation. For almost all the wood species, the creep deformation during the microwave irradiation exceeded remarkably the deformation at failure in static bending test carried out at about 100°C on water-saturated specimens. The magnitudes of the residual deformation varied among the different wood species tested such as softwood, ring porous wood, and diffuse porous wood. However, the difference in the deformation behavior cannot be explained in terms of the morphological differences among these woods. This fact suggests that the difference in the bending quality may be ascribed to that in the cell-wall structure, especially to the composition of lignin and hemicellulose in the matrix of the cell wall. Furthermore, the results of SEM observation indicated that both the arrangement of the cells and the cell shape in the cross section charged remarkably by the bending treatment. However, neither the collapse nor the failure of the cell wall was detected. The fact suggests that the cell wall materials were softened remarkably during the microwave irradiation.
Young's modulus of the cell wall in longitudinal direction, which varies widely not only among the different wood species but also within the same species, is closely related to the bending quality of wood. In order to explain this observation, we made measurements of Young's modulus, crystallinity and microfibril angle for numerous softwood species. The experimental values of the average dynamic Young's modulus of the cell wall ranged from 4.5×1011dyn/cm2 to 6.4×1010dyn/cm2. Species having extremely low value of this modulus showed low degree of crystallinity and large microfibril angle. On the other hand, the Young's modulus of the cell wall was theoretically estimated using a cell-wall model, in which the distribution of chemical constituents and microfibril angles in the cell-wall layers are taken into account. The effects of crystallinity, microfibril angle and elastic constants of matrix on the Young's modulus of the cell wall was examined according to this theory. From these results it was proved that the Young's modulus of the cell wall depend strongly on microfibril angle and that the main reason for the variation of the Young's modulus of the cell wall and the bending quality among the different species is resulted from the variation of microfibril angle.
To clarify the factors affecting apparent viscosity ηa of tobacco powder-water systems and to formulate an emprical equation for ηa experimental results are rearranged, and supplementary tests have been conducted for the pressure transmittances for those of Bright Yellow-water systems and of Matsukawa-water systems. The following results have been obtained; The ratio of pressure transmittances changed remarkably at 0.13 in moisture content for Bright Yellow-water systems, and at 0.20 for Matsukawa-water systems. These values are smaller than those of the systems of each residues by 0.25~0.23. Dependencies of ηa on shear rate are expressed by Cross's equation. However, m=2/3 is inadequate to represent the results, in this study. Good agreement between experimental results and the equation is found at m=0.70~0.85. Dependencies of ηa on volume fraction are expressed by Eilers's equation. For the upper limit of volume fraction,φm employed is the volume fraction at the critical moisture content which is estimated from the transmitting characteristics. Dependencies of ηa on temperature are expressed by Andrade's equation. Constant B is determined for the systems of two types of tobacco, and B increases according to the decrease of ψ.