Elasticity of the intercrystallite zones and the mechanical properties of oriented polymers

As a result of a study of the behavior under load of the elements of the supermolecular structure of oriented amorphous-crystalline polymers it is shown that the stresses on the crystallites and the amorphous zones in series with them in the direction of the chain axes are equal to the mean stress applied to the specimen along the orientation axis. The nature of the elasticity and deformability of the amorphous zones is analyzed. A relation is obtained between the strength properties of oriented polymers and the number of load-carrying chains in the amorphous zones.Ioffe Physico-Technical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 1002–1007, November–December, 1969.     

Uniaxial deformation of partially crystalline oriented polymers (fibers)

The uniaxial deformation of partially crystalline oriented polymers is examined under the following assumptions: the volume of the specimen is constant, deformation is affine, stable and reversible, and the crystallites are only slightly deformable as compared with the deformation of the amorphous part. A general expression is obtained for the applied load as a function of the crystallinity, anisotropy factor, and relative elongation. The following cases are considered: isotropic, completely amorphous specimen; isotropic, partially crystalline specimen; and highly oriented, partially crystalline specimen. The results obtained are compared with experimental data.Mekhanika Polimerov, Vol. 3, No. 1, pp. 24–28, 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.     

Conoscopic investigation of the optical properties of kapron and polyethylene monofilaments

The conoscopic method of investigation is applied to anisotropic crystalline polymers (kapron and polyethylene monofilaments). The conoscopic figures obtained for various stretch ratios show that the optical properties of the monofilaments are similar to those of biaxial positive crystals and can be characterized by an optic indicatrix in the form of an ellipsoid with three nonequal principal axes. The angle of the optic axes 2E is the measured parameter of the optic indicatrix. This angle varied with the stretch ratio and over the cross section of the monofilaments. The variation of the angle 2E with stretch ratio may be associated both with orientation of the crystallites and with the nature of the packing in the crystalline regions of the monofilament. The variation of the angle 2E over the cross section of the monofilaments indicates nonuniformity of the optical properties in the radial direction.T. G. Shevchenko Kiev State University. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 598–602, July–August, 1968.     

Limiting stretch ratios of polymers. Role of molecular mobility

Orientation stretching stops before the polymer chains reach full orientation. The reason for the cessation of stretching in linear polymers is considered to be the decreased kinetic flexibility of the macromolecules. With Kapron as an example, it has been demonstrated, using NMR, that on attainment of the limiting stretch ratio under the action of the stretching (orienting) forces, segmental motion in the amorphous regions is almost completely stopped: the amorphous regions are glassy at any orientation temperature, even those close to the melting point of the crystals. The orientation process stops because the polymer under load behaves like a rigid body devoid of rubber-like elasticity.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 387–391, 1973.     

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.     

Temperature — Time dependence of the strength of polymers exposed to UV radiation

Experiments on several polymers have shown that the dependence of the radiation lifetime under load on the intensity of the ultraviolet radiation and test temperature is governed by general empirical laws. An analysis of the results yields important information on the photodegradation of stressed polymers.Ioffe Physico-Technical Institute, Academy of Sciences of the USSR. Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 442–448, May–June, 1969.     

Lifetime of amorphous polymers under intermittent loading

The lifetimes of two types of amorphous polymers (polyvinyl chloride and plasticized epoxy resin) under intermittent loading have been investigated. It is established that the lifetime, determined without allowance for recovery time, is less than that under constant load. Under periodic loading at constant stress the lifetime varies with the loading regime. For each of the investigated polymers a lifetime minimum is observed at a certain duration of the loading and recovery periods.Higher Chemical Technology Institute, Sofia. Translated from Mikhanika Polimerov, No. 5, pp. 912–916, September–October, 1971.     

Strength and deformability of reinforced polymers in tension normal to the fibers

The strength and deformability of reinforced polymers in tension across the fibers is investigated. It is assumed that the polymer deforms as an ideal elastoplastic body. Relations are obtained for the nature of the deformation of the polymer between the fibers and the strength and deformability of the composite with allowance for the structural distribution of the components. Theoretical stress-strain diagrams are presented for composites with different reinforcement densities and resin elasticities. The theoretical values of the strength and deformation of reinforced polymers with the load applied across the fibers are compared with the results of experiments on model specimens of epoxy-Thiokol polymers.Leningrad Mechanical Institute. Translated from Mekhanika Polimerov, No. 4, pp. 682–687, July–August, 1970.     

Deformation properties and texture of isotactic polypropylene fibers

The deformation properties of isotactic polypropylene fibers are compared with the fraction of crystallites in thea and c textures and with their orientation.Institute of High-Molecular-Weight Compounds, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 7–10, January–February, 1971.     

The half-widths of the bands due to the skeletal vibrations of polyethylene molecules,free and under an applied load

The third-order phonon interactions in free polyethylene chains and polyethylene chains under load have been analyzed to obtain the theoretical temperature dependence of the half-widths of the bands due to the skeletal vibrations potentially active in the absorption and Raman spectra. The problems of the harmonic and anharmonic vibrational analysis of polymers under load are discussed.A. F. Ioffe Order of Lenin Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 3–11, January–February, 1972.     

Propagation of sound in oriented polymers

The propagation of sound in oriented polymers is considered. Starting from an assumption concerning the superposition of relaxation processes in polymers, expressions are obtained for the speed and absorption of sound as functions of the relaxation spectrum, molecular orientation, and crystallinity. It is shown that the orientation dependence of the acoustic properties is more distinctly expressed in the region of the glassy state.Scientific-Research Institute of Plastics, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 437–441, May–June, 1969.     

Molecular mechanism of orientation in polymers

On the basis of calculations in which the behavior of the chain under load is investigated, it is suggested that, apart from the rotational isomerism mechanism, at low temperatures and high stresses the instability of the folded configuration may play an important part in polymer orientation. A distinctive feature of the proposed mechanism is the high rate of orientation, which for an isolated chain is of the order of the speed of sound.T. G. Shevchenko Kiev State University. Translated from Mekhanika Polimerov, No. 3, pp. 525–528, May–June, 1976.     

Study on the impact-shear viscosity of block polymers

The temperature dependence of the specific impact viscosity of several amorphous and amorphous-crystalline polymers as measured in tests by means of the authors' impact-cutting method is discussed. It is shown that this dependence agrees fairly well with the mechanical losses determined at the same interaction frequencies and, hence, is sensitive to the relaxation transitions in polymers (an enhanced impact stability corresponds to the transition regions). The similarity mentioned above and the correspondence between the temperature dependences of the density, the Poisson coefficient, and the elasticity modulus suggests that mechanical energy supplied is dissipated by a molecular-motion type including segment motion and relating to melting of the crystallites.S. M. Kirov Leningrad Institute of Textile and Light Industry. Translated from Mekhanika Polimerov, No. 2, pp. 226–230, March–April, 1972.     

Effect of ultraviolet radiation on the lifetime of polymers under load in the low-stress region

In the low-stress region the lifetime of polymers placed under load in the presence of UV radiation is appreciably greater in a vacuum than in air. This indicates that the ambient medium plays an important part in the process of restoration of broken bonds and that the knee on the log =f() curve is at least partly due to recombination processes.Ioffe Physico-Technical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 929–931, September–October, 1969.     

Change of strength of polymeric materials in the process of orientation

In the process of orientation the strength of polymeric materials changes as a result of a net increase in the number of ordered structural elements. It is shown that the model obtained can be used to predict the effect of orientation on the strength of polymers. The theoretical relations satisfactorily describe the available experimental data.Scientific-Research Institute of the Tire Industry, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 848–853, September–October, 1970.     

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 Poisson's ratio of certain crystalline polymers under a constant compressive load

The results of an investigation of the Poisson's ratio in compression for two crystalline polymers, low-density polyethylene and teflon, are given. The effect of time under load and temperature on the value of the Poisson's ratio is examined.Mekhanika Polimerov, Vol. 1, No. 4, pp. 43–46, 1965     

Damage to transparent polymers caused by laser pulses lasting 10−3 and 10−8 sec

A study has been made of the internal damage produced in transparent polymers by laser pulses lasting 10^–3 sec (free-generation mode) and 10^–8 sec (giant-pulse mode). It has been established that in these cases different mechanisms are responsible for the damage. The action of giant laser pulses on transparent polymers evidently provides the first and so far only means of studying fracture effects associated with the truly instantaneous application of load, i. e., when the load application time is much less than the fracture time.Mekhanika Polimerov, Vol. 3, No. 3, pp. 493–497, 1967     

Acoustic determination of molecular orientation in polymers

On the basis of the results of measurements of the ultrasonic propagation velocity in polyethylene terephthalate fibers it is shown that the Moseley formula is suitable for determining the molecular orientation of both amorphous and amorphouscrystalline polymers. The dependence of the molecular orientation factor of amorphous and crystalline specimens of polyethylene terephthalate on the draw temperature and draw ratio is investigated. The effect of polymer orientation on the ultrasonic shear-wave velocity in the fiber is studied.Kiev Branch, All-Union Scientific-Research Institute of Artificial Fibers. Translated from Mekhanika Polimerov, No. 1, pp. 26–34, January–February, 1976.