Structural models and rheological properties of particle-dispersed systems are briefly reviwed. Among a number of models, ever proposed to describe the rheological behavior of the complex systems, three models of Goodeve-Gillespie, Cross, and Ruckenstein-Mewis are compared with one another from the viewpoints of the time-dependent behavior of the rate equation and the predicted viscosity behavior in the steady state. No remarkable difference in the time dependence of structural parameters is expected in the short time range, but in the equilibrium state, they differ from one another depending on the models. Calculated steady flow viscosities from the models are proportional to the n-th power of the ratio of the rate constant of link formation to that of link breaking, n varying with the models. Finally, shown are the steady flow and rheopexy properties of particle dispersed systems predicted from a two-step structural model, which was recently proposed by the auther.
The viscoelastic properties of disperse systems of polybutadiene particles in polystyrene solution were measured, and the effects of particle content and molecular weight of polystyrene in matrix solution on the viscoelastic properties were discussed. The temperature dependence of viscoelastic function is well-expressed by the WLF equation, taking a reference temperature Ts for each particle content. Ts increases with particle content. The rubbery plateau modulus Ge increases with particle content, but it is independent of molecular weight of matrix polymer. The relative stiffness of the particle to that of matrix phase determines the rubbery plateau modulus of the system. The characteristic relaxation time for entanglements of the matrix solution is affected by the particle content and the molecular weight independently. The modulus of the second plateau depends not only on particle content but also on molecular weight of matrix polymer. The modulus also depends on the molecular weight of polystyrene grafted on the surface of polybutadiene particles.
Molecular structural parameters such as number-average molecular weight(Mn), weight-average molecular weight(Mw), and long-chain branching frequency of low-density polyethylenes (LDPE) synthesized by an autoclave and a tubular reactor were evaluated from GPC and intrinsic viscosity data on the basis of the method developed individually by Drott and by Kurata. In Drott's procedure, the contraction factor g derived for unfractionated materials was used. On the other hand, g derived for fractionated materials was used in the Kurata's procedure. Here g is the ratio of root-mean square radii of the branched and linear polymers with the same molecular weight. Values of Mn or Mw obtained by the two procedures were almost the same but long-chain branching frequencies evaluated by Kurata's procedure were considerably larger than those of Drott's one. In order to evaluate which procedure would provide more adequate long-chain branching frequencies, the long-chain branching frequencies were also evaluated on the basis of 13C-NMR spectra and compared with those obtained by means of GPC and intrinsic viscosity measurements. However we could not obtain a definite conclusion from such a comparison. The relationships among melt index (MI), density, and molecular structural parameters were also investigated. It was found that (i) MI can be predicted from Mw and long-chain branching frequency, and (ii) the long-chain branching frequency of autoclave resins increases with decrease in their density.
When low-density polyethylene (LDPE) is subjected to shearing force in the molten state, its melt viscoelastic properties considerably vary though its primary molecular parameters such as weight-average molecular weight, molecular weight distribution, and long-chain branching frequency do not change. Such an experimental fact indicates that it is indispensable to clarify the shearing histories of the materials for a comprehensive understanding of the rheological behavior of LDPE melts. The materials, on which definite shearing histories were imposed, were prepared by means of solvent- or shear-treatment, and the following experimental results were obtained. (1) The zero-shear viscosities of the solvent-treated materials were larger than those of the sheared ones. (2) The empirical equation of Cox-Merz did not hold for the solvent-treated materials, but held for the sheared ones. (3) The flow-activation energy of the solvent-treated materials was dependent on the materials but that of the sheared ones was independent of the materials. These experimental results were discussed in terms of a concept of rheological flow units.
Wood bending utilizing microwave heating was investigated. In the first place, a creep test for Quercus crispula having various moisture contents during irradiation with microwave was carried out and the effect of the initial moisture content φ0 on the final creep deflection Ycf was examined. The relation between Ycf and φ0 was expressed by Ycf=4√φ0. In the next place, the bending quality of nine kinds of softwoods and hardwoods was compared. The rating of the bending quality was based on the radius of curvature of a bent member. The bending quality varied among the different wood species and as a rule that of hardwoods was better than that of softwoods. Robinia pseudo-acacia and Pinus taeda could be bent to a 3 cm radius in 1 cm thickness without any compressive wrinkles and tensile failures. An attempt was also made to correlate the bending quality with the specific gravity of wood and such mechanical properties of water saturated wood specimens as modulus of elasticity, stress and strain at proportional limit and maximum load and deflection. The mechanical properties were measured by a static bending test at 20°C. A good correlation was found between bending quality and maximum deflection. Furthermore, the anatomical structure in cross section of the bent wood was examined through a microscopic examination. Regular array of cells in radial direction which is common in the untreated wood became disordered by the bending treatment, which suggests that the cell wall materials were softened remarkably during irradiation with microwave.
An AB-diblock copolymer in a highly selective solvent such as poly (styrene-b-butadiene) diblock copolymer/n-paraffin solutions has a micellar structure and shows a thixotropic flow with a yield stress. The dynamic stress for small-amplitude sinusoidal strain of such a system contains higher odd harmonics, and their contributions to the whole stress diminish as the frequency is increased. Such a nonlinear behavior can be qualitatively described by a simple Bingham-type viscoelastoplastic model, which consists of a Bingham model connected in series with a spring. The oscillatory Couette-flow behavior of 10% SB/n-tetradecane solution was simulated by this model by considering the presence of two dimensional plug flow. The model suggests that the thickness of the plug region alters periodically, and the angular velocity profile in the solution is not sinusoidal because of the plasticity.
Krigbaum's modulus theory and its application to polyethylene which was irradiated with γ-rays are discussed, and the following conclusions were obtained. Amorphous chain in crystalline polymer varys from inverse Langevin chain to Gaussian chain with increasing temperature. Krigbaum's parameter Nn(t), which is the average number of statistical segments present in an amorphous chain when the two ends have just deposited themselves on the surface of growing crystallites, does not depend on the degree of degradation of the samples. The ratio of the theoretical initial Young's modulus for the degraded sample to that for the undegraded sample, E0(t)/E0(0), increases with the degree of degradation of the samples.
Krigbaum's modulus theory, which was based on an assumption that amorphous chains in crystalline polymers were nearly fully extended without an external force, was applied to chemorheology of crystalline polymers. We derived the following chemorheological equation for crystalline polymer from Krigbaum's modulus theory. _??_ It was found that the theoretical values of the ratio of the initial Young's modulus for the degraded samples to that for the undegraded samples, E0(t)/E0(o), increase with the increase in the degree of degradation. The tendency agrees well with that of experimental data. It seems to be caused by the increase in the degree of crystallinity accompanied by degradation. Such an increase may be contributed predominantly by crystallization of some of the remaining unsevered chains in the amorphous region.