Relationship between internal stresses and rheological properties

It is shown that, under practically identical viscous-shear conditions, the correlation between orientation and relaxation processes taking place in an extruder die is different for different brands and batches of shock-resistant polystyrene. It has been found that the material with the the higher orientation tendency in the viscous-fluid state in the die is oriented more strongly at the same conditions in the Mackian elasticity state in the reception and pulling of the extruded polymer. It is shown that the thermal shrinkage of the sheets correlates reasonably well with the degree of swelling and the Mackian elasticity deformation of the polymer."Plastpolimer" Scientific-Industrical Association, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 952–955, September–October, 1972.     

Modification of the mechanical properties of synthetic fibers by grafting vinyl monomers

Graft polystyrene has been synthesized on polypropylene fibers. The isometric heating curves of the grafted fibers have two maxima. The first is associated with the preserved oriented polypropylene structures, the second with the oriented structures formed directly in the process of polystyrene synthesis. The maximum stress corresponding to the latter maximum is proportional to the amount of polystyrene and the degree of orientation of the starting polypropylene and depends on the mechanical stress in the fiber during the process of polystyrene synthesis.Mekhanika Polimerov, Vol. 3, No. 6, pp. 963–969, 1967     

Effect of the molecular weight of polystyrene on the viscosity of concentrated solutions

The viscosity of solutions of polystyrene of various molecular weights (from 1.04 · 10² to 3.8 · 10⁵) in a poor solvent (decalin) and a good solvent (ethylbenzene) has been measured at temperatures from 15 to 70°C over a broad range of shear stresses from 10² to 10⁶ dyne/cm². The nature of the solvent has a considerable influence on the critical molecular weight and the absolute value of the viscosities of the solutions over the entire range of molecular weights and on the form of the flow curves of decalin solutions of polystyrene as a function of temperature. The heat of activation of viscous flow increases with increase in molecular weight and shear stress on the interval 20–80°C. The results obtained are explained in terms of the effect of the molecular weight of the polymer, the nature of the solvent, stress and temperature on structure formation in the solution and on the orientation of the macromolecules and structures in the flow process.Ural Gor'kii State University, Sverdlovsk. Translated from Mekhanika Polimerov, No. 5, pp. 920–926, September–October, 1970.     

Effect of the molecular weight of the polystyrene matrix on the physicomechanical properties of impact polystyrene

The effect of the molecular weight of the polystyrene on the properties of impact polystyrene obtained by mechanical mixing of polystyrene and rubber has been investigated. As the molecular weight of the polystyrene increases, the physicomechanical properties of the impact polystyrene improve and its rheological properties deteriorate. There is a definite correlation between the physicomechanical properties of the polystyrene and those of the impact polystyrene.Scientific-Research Institute of Synthetic Rubber, Kralupy-on-Vltava, Czechoslovakia. Translated from Mekhanika Polimerov, No. 3, pp. 545–546, May–June, 1971.     

Experimental determination of the limiting birefringence of oriented polymers

Experimental data on the birefringence and molecular orientation factorf, determined from the IR absorption spectra in polarized light, are compared for polystyrene, polyvinyl alcohol, and polyethylene. Limiting values of the birefringence corresponding to maximum orientation (f=1) for these polymers are found to be equal to 0.16, 0.063, and 0.065, respectively.Mekhanika Polimerov, Vol. 3, No. 6, pp. 1105–1109, 1967     

Relation between molecular orientation characteristics determined from birefringence and acoustic data and the effect of orientation on the strength of polycaprolactam fibers

The mean molecular orientation calculated from birefringence and acoustic data has been investigated in relation to the degree of stretching for polycaprolactam fiber. A correlation has been found between the characteristics calculated by these two independent methods. It is shown that the molecular orientation factor calculated from the speed of sound does not depend on crystallinity if the measurements are made below the glass transition temperature. It is confirmed that the strength of the fiber depends importantly on the degree of orientation of the molecular segments in the amorphous zones.Mekhanika Polimerov, Vol. 3, No. 1, pp. 3–7, 1967     

Study of the prefracture states of rigid polymers 1. Forced high-elastic deformation

It is shown that in the process of extension specimens of a rigid unoriented polymer — polyethylene terephthalate — go over into the oriented state before failure. Various cases of transition to the oriented state are considered: with the formation of a neck and deformation bands, with and without loss of continuity. The degree of molecular orientation of the specimens and their fracture conditions are estimated.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 8–14, January–February, 1976.     

Birefringence and stress-strain diagrams for oriented atactic polymethyl methacrylate and polystyrene films

The stress-strain diagrams of amorphous linear polymers oriented under different conditions are examined; a comparison is made with the parameters of their internal structure. It is shown that the shape of the diagram for rigid polymers is basically determined by the degree of orientation of the links of the macromolecules irrespective of the molecular weight of the polymer and the extension conditions. It is established that the moment of failure can not be determined from this parameter alone. It is found that when the oriented polymer is tested close to the softening point the correlation between the shape of the diagram and the birefringence, characterizing the degree of orientation of the links of the macromolecules, is disturbed.Mekhanika Polimerov, Vol. 2, No. 3, pp. 435–439, 1966     

Fracture mechanism of amorphous polystyrene

The degradation products of polystyrene film specimens have been recorded and their accumulation kinetics in the presence of uniaxial tensile stresses have been studied at various temperatures. It is shown that the accumulation kinetics satisfy the Arrhenius equation for reactions in a mechanical field. The equation for the rupture life can be written in terms of the corresponding parameters of the mechanical degradation reactions. It is concluded that the rupture life and strength of polystyrene depend on the kinetics of mechanical degradation of the polymer chains.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 541–544, May–June, 1975.     

Opticome chanical method of studying changes taking place in the molecular structure of polymers under the influence of external actions

The results of investigations into the behavior of certain polymer films subjected to mechanical action are presented. Special attention is paid to the orientation of the molecular lattice which accompanies the deformation of the sample. As a structure-sensitive method the optical polarization technique is employed. The apparatus specially designed for the measurements in question is described. Results are given for cis-polybutadiene rubbers differing in their molecular-weight distribution and polycarbonate films differing in their degree of stretch.S. V. Lebedev All-Union Scientific-Research Institute of Synthetic Rubber, Leningrad. Translated from Mekhanika Polimerov, No. 2, pp. 209–213, March–April, 1972.     

Investigation of the relaxation process in polycarbonate film

The temperature relaxation of polycarbonate film and the accompanying change in the birefringence path difference are considered. It is shown that at a temperature of about 170°C intense crystallization takes place in the film. The deformation modulus is a function of the density of the network and its degree of orientation. The variation of these parameters with the stretch ratio and temperature is determined experimentally. The creep of polycarbonate film is considered and correlated with the curves representing the fall in the number of chains of the molecular network in pure relaxation.Mendeleev All-Union Scientific-Research Institute of Metrology, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 72–76, January–February, 1973.     

Uniaxial extension of polystyrene with a constant true stress

A apparatus designed for the extension (stretching) of yielding polymers at a constant true stress is described. The changes taking place in the general, rubber-elastic, and irreversible deformations aredetermined, together with the corresponding rates of deformation, as well as the viscosity and relaxation characteristics, during the extension (tensile strain) of block polystyrene at various constant true stresses and a temperatore of 130°C.All-Union Scientific-Research Institute of Synthetic Fiber, Kalinin. Translated from Mekhanika Polimerov, No. 6, pp. 1104–1109, November–December, 1972.     

On the theory of biaxial orientation of amorphous polymers

The macromolecule orientation distribution function for biaxial orientation is calculated on the basis of a network model of a linear amorphous polymer. The dependence of the distribution function on the biaxial stretch ratio, orientation temperature, and certain other factors is investigated. A relation is established between the distribution function and the experimentally observed birefringence. The birefringence of biaxially oriented polymethyl methacrylate is measured in relation to the degree of deformation. The experimental data are compared with theory.Moscow Lenin State Pedagogical Institute, Problem Laboratory of Polymer Physics. Translated from Mekhanika Polimerov, No. 5, pp. 771–779, September–October, 1970.     

Investigation of the working region of kapron fibers

Kapron fibers with various stretch ratios have been subjected to tensile stress relaxation tests at constant clamped length. The relaxation constants — activation energy U₀ and the coefficient — are calculated from the results of the experiments. It is shown that the fiber parameters U₀ and depend on the given molecular orientation.All-Union Scientific-Research Institute of Synthetic Fibers, Kiev Branch. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 736–739, July–August, 1968.     

Effect of gamma radiation on the cracking and mechanical properties of Kapron (polycaprolactam)

The results of a mechano-optical investigation of irradiated oriented polycaprolactam film are discussed. After irradiation comparatively large cracks running at right angles to the orientation axis appear in the film; these are responsible for the reduced tensile strength and deformability of the polymer.Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad; Lenin Tadzhik State University, Dushanbe. Translated from Mekhanika Polimerov, No. 4, pp. 756–758, July–August, 1971.     

Biaxial orientation of amorphous linear polymers

The dependence of the birefringence and orientation stress on the biaxial stretch ratio and orientation conditions has been experimentally investigated. The temperature dependence of these characteristics is explained in terms of the network structure of amorphous polymers. It is shown that the transformations of the supermolecular structures in the process of biaxial orientation depend on the orientation temperature — at higher temperatures better organized structures are formed. There is a formal relationship between the effect of orientation temperature on supermolecular structure formation and on the relaxation process responsible for the formation of a more thermally stable molecular network.Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 17–23, January–February, 1971.     

Investigation of the temperature strain relaxation of urethane elastomers by the opticomechanical method and infrared spectroscopy

The data of an experimental investigation of polyester- and polyether-based elastomers are presented. The elastomers were investigated in creep while increasing the temperature in steps of 20°C. Infrared absorption spectra were obtained for a series of loads and temperatures and the variation of the total orientation of the molecular structure (birefringence) and the growth of the deformation with time were recorded. An attempt is made to interpret the changes in the rates of orientation of the molecular structure by varying the concentration of certain characteristic chemical bonds.Translated from Mekhanika Polimerov, No. 3, pp. 437–441, May–June, 1975.     

Effect of orientation and molecular weight on the modulus of elasticity of polymer materials

The modulus of elasticity of a perfectly crystalline polymer is calculated as a function of the orientation of the crystallites. The calculations are based on the mechanics of a micro-inhomogeneous continuum. The dependence of the modulus of elasticity on crystallite orientation and molecular weight is calculated with reference to the example of crystalline kapron.Moscow-Lenin Pedagogical Institute. Problem Laboratory of Polymer Physics. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1002–1007, November–December, 1968.     

Effect of molecular weight on strength and deformation characteristics of oriented amorphous polymers

Tensile tests were carried out on uniaxially oriented films of several amorphous linear polymers (polymethyl methacrylate, polystyrene, and poly-2,2-octamethylene-5,5-dibenzimidazol) of various molecular weights. It was shown that molecular weight has no direct effect on polymer strength, which is determined by structure. However, when polymer fibers and films are formed and stretched, the molecular weight of a given material affects the orientation of macromolecules and so predetermines the structure of the products obtained and, consequently, their strength.Mekhanika Polimerov, Vol. 3, No. 4, pp. 579–585, 1967     

Elasticity of the crystal lattice of polyethylene terephthalate

The elasticity of the crystal lattice of polyethylene terephthalate was studied along and across the axes of the polymer molecules. The elastic modulus across the chains depended on the degree of crystallinity and the interplane distances in the directions of thea and b parameters of the unit cell. The nature of the elastic deformation in the crystal lattice was analyzed, and its elastic modulus along and across the axes of the chains was calculated. On loading biaxially oriented amorphous-crystalline polymers with a tensile stress applied in the direction of one of the orientation axes of the polymer, the stresses in the crystallites oriented along and across the external applied force and the amorphous regions in series with them were equal to the stress in the sample averaged over the cross section.Deceased.Translated from Mekhanika Polimerov, No. 6, pp. 982–986, November–December, 1972.