Moscow, U.S.S.R., 1977, 438 pp. Rub. 3.16.Chapter 1 (nearly a quarter of the book) deals with the basic notions of rheology to which the stress tensors and deformation tensors belong, and in which elastic solids, viscous liquids, and viscoelastic materials are considered. The treatment is mathematical and general, so that the main concern is with rheology rather than with polymers. In Chapter 2, equally long, on viscosity in shear flow, experimental data are used to illustrate the validity of the equations derived (such as the temperature superposition rule), but the theory still predominates. Fully eight sections in this chapter have headings such as A's theory, B's theory, etc.The next 90 pages are taken up by relaxation (viscoelastic) properties of flowing polymer systems. Here also many mechanical models of these systems are clearly and critically discussed. Chapter 5 is shorter and devoted to the normal shear stresses (the Weissenberg effect), including the flow birefringence. The next chapter is on high elasticity of liquid polymers; and the last is on uniaxial extension of polymers.The book certainly can be recommended to anyone working in one of the above mentioned areas of science (and can read Russian). A peculiarity of the text is that, although so many ideas and experimental data are covered, literature references are distinctly scarce. We find, e.g., on p. 176, eleven empirical equations relating the effective viscosity to the shear rate or the shear stress, but no authors are quoted. J. J. Bikerman 15810 Van Aken Blvd. Shaker Heights, Ohio
The dynamic shear modulus and the flow rate through capillaries under constant pressure and under constant velocity of the piston, have been measured for polybutadienes and polyisoprenes of narrow molecular weight distribution with molecular weights ranging, respectively, from 3.8 × 104 to 5.8 × 105 and from 1.06 × 105 to 6.02 × 105. The phenomena of the discontinuous increase of volume flow rate and self‐oscillatory flow regime at critical rates of deformation have been considered in detail. It is proposed that these phenomena are due to the induced transition of the polymer from the fluid to the high‐elastic state at higher deformation rates. As a result, an inference has been made that polybutadienes and polyisoprenes with a narrow molecular weight distribution in the high‐elastic state, behave in certain respects as crosslinked polymers incapable of displaying fluidity. The quantitative relationships among the viscoelastic characteristics measured under dynamic regimes, the parameters determining the critical flow regimes, and the molecular weights of polybutadienes and polyisoprenes have been worked out.
Methods of capillary viscometry were used in studying the rheological properties and behavior of a broad range of rubbers, including polymers with narrow and wide molecular-weight-distribution as well as commercial rubber grades, at widely varying shear rates and stresses. As is shown, in full conformity with the previously conducted experiments, during transition from a fluid to highelastic (quasi-cross-linked) state, they are chracterized by spurting followed by sliding over the channel walls. This relaxation transition is characterized by a critical shear stress value invariant with respect to the molecular weight, molecularweight distribution and temperature. The parameters defining spurting of polymer flow as a function of molecular-weight characteristics, temperature, and channel geometry have been investigated in detail. It is shown for the first time that under supercritical conditions the rate of polymer flow through channels does not depend, in the first approximation, on the molecular weight of the polymer, its molecularweight distribution, temperature, and filling, but is determined only by the shear stress.
The behavior of narrow molecular weight distribution polymers has been investigated under uniaxial extension at constant deformation rate and at constant stress. It has been established that up to rupture these polymers behave as linear viscoelastic bodies. A detailed investigation of the rupture phenomenon has shown that the rupture of fluid polymers is due to their transition to the rubbery state at critical deformation rates, with the result that they disintegrate like quasi‐cured rubbers. The effect of the temperature and the molecular weight on the critical conditions of rupture has been described in terms of viscoelastic relaxation.
Blends of polyoxymethylene (POM) with a copolymer of ethylene and vinyl acetate (CEVAc) have been studied. The effect of viscosity ratio for melts of the components on the processes of fiber formation in extrudates and on the rheological properties of the molten blend has been tested. The viscosity ratio of the fiber‐forming POM and the matrix varied in the range 0.35‐27.7. POM ultrathin fibers of unlimited length can be formed in the CEVAc only at a viscosity ratio close to unity. For ratios much greater than unity, the extrudate is found to contain short fibers and a finely dispersed powder or no fibers at all. If the viscosity of the POM melt is lower than that of the matrix, films are formed in addition to fibers. The second factor that governs fiber formation is the extrusion shear stress. An optimum shear stress exists at which the amount of ultrathin fibers is a maximum.
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