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.     

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.     

Study of the effect of various factors on the low-temperature strength of polyethylene with graft polyacrylonitrile

Low-density polyethylene film has been subjected to graft polymerization with acrylonitrile. The effect of the graft polymerization conditions and subsequent treatment on the strength of the grafted film has been investigated. The strength was measured at -196°C. The grafted film behaves like a heterogeneous material in which the unoriented polyacrylonitrile macrostructures play the part of filler particles. The strength of the grafted film is additively composed of the strengths of the polyethylene and the polyacrylonitrile and the change in strength after stretching, heating, and other treatments is determined by the changes in the degree of orientation of the polyethylene.V. I. Lenin Belorussian State University, Minsk. Translated from Mekhanika Polimerov, No. 4, pp. 589–593, July–August, 1973.     

Strength properties of polymer films subjected to continuous tearing

Using the principle of tearing at a constant velocity and applying this to samples with longitudinal notches, a method of recording the tearing strength as a continuous function of temperature, crystallization time, and other factors which continuously vary the state of a (polymer) film material is developed. The characteristic points of the temperature transitions are determined for a number of polymer films in relation to their mechanical (strength) properties. The crystallization kinetics of polyethylene terephthalate films are analyzed.Scientific-Research Institute of Plastics, Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 257–261, March–April, 1972.     

Creep of polyethylene terephthalate with variable stresses under conditions of uniaxial extension

The results from experimental and theoretical investigation of the creep of polyethylene terephthalate film during stepwise varying stresses under conditions of uniaxial extension are given.Izhevsk Mechanical Institute. Translated from Mekhanika Polimerov, No. 5, pp. 929–933, September–October, 1972.     

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.     

Study of the supermolecular transitions associated with the reorientation of high-pressure polyethylene film

Small-angle optical and X-ray diffraction techniques have been used in a comparative study of the processes of orientation and reorientation of high-pressure polyethylene film. It is shown that at large stretch ratios both processes are governed by the same laws. In these supermolecular transitions it is possible to observe spherulite-macrofibril conversions during orientation and macrofibril-macrofibril conversions during reorientation, a direct genetic relationship being preserved between the dimensions of the starting spherulites or macrofibrils and the dimensions of the macrofibrils formed by stretching. However, the major period of the oriented film, the basic element of the microfibrils forming the macrofibril, is independent of the major period of the starting film and depends only on the temperature at which stretching is carried out.Institute of High-Molecular Compounds, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 771–777, September–October, 1969.     

Infrared spectroscopic study of the prefracture state of rigid polymers

A correspondence has been established between the effects of stress and temperature on the half-width and the position of the maximum of the 972-cm^–1 absorption band for polyethylene terephthalate. It is shown that the prefracture state of polyethylene terephthalate is a softened state.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 520–523, May–June, 1976.     

Relation between deformation and rotational isomerism

In uniaxially oriented polyethylene and polyethylene terephthalate films conformational transitions were studied by the absorption IR-spectroscopy method during deformation of the specimens carried to rupture in a wide range of temperatures and with different loading methods. It is shown that upon elongation of the polymers the concentration of trans isomers increases and that of gauche isomers decreases. A linear unique relation is obtained between the number of rotational isomers and magnitude of deformation in the amorphous parts of the investigated polymers. It is hypothesized that the conformational transitions determine the magnitude of deformation of amorphous-crystal-line polymers.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 1077–1080, November–December, 1975.     

Calculation of one-dimensional polymer creep under stepped loading

A graphic method is proposed for calculating polymer creep under stepped loading. The method is based on the equations of nonlinear viscoelasticity. It can be used to describe the aftereffects of specimens of polyethylene terephthalate film and the creep of tubular plexiglas specimens at sharply varying stresses. The agreement with experimental data is satisfactory.Mekhanika Polimerov, Vol. 3, No. 4, pp. 671–675, 1967     

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.     

Stress on the interatomic bonds near the surface of a polymer

The stresses on the interatomic bonds in the interior and at the surface of polyethylene terephthalate film in uniaxial tension have been determined by means of infrared transmission and reflection spectroscopy. The stresses are found using the shift in the frequency of the atomic vibrations produced by the application of a mechanical load. It is shown that the stresses on some bonds in the specimen reach 700 kgf/mm², i.e., approach their theoretical strength. The concentration of these bonds in a surface layer 1 µ thick is approximately an order greater than the concentration in the interior of the specimen.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 512–514, May–June, 1976.     

A polymer film hardening effect

It is shown that a polyester film incapable of forced high-elastic deformation can be subjected to such deformation by stretching a film-substrate system. The resulting oriented structure is stable and on being measured from the substrate, the film exhibits a hardening effect. In this case contact with and adhesion to the substrate are a necessary condition for the development of the latent potential of the film.Lenin All-Union Electrical Engineering Institute, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 731–733, July–August, 1971.     

Development of slits in polyethylene and polypropylene films stressed in uniaxial tension

Optical microscopy has been used to investigate the development of a slit in polyethylene and polypropylene films with spherulites of different types and sizes stressed in uniaxial tension. The angle between the slit and the direction of extension was 0, 45, or 90°. Slits at 45 and 90° initially develop through localization of slits by a stronger oriented polymer and subsequently as a result of failure of the oriented polymer at the tip of the slit. A longitudinal slit does not develop and does not affect the deformation of the film.Mekhanika Polimerov, Vol. 3, No. 1, pp. 95–98, 1967     

Modeling the influence of mineral content and porosity on ultrasound parameters in bone by using synthetic phantoms

Model composite media – 10×15×80 mm³ bone tissue phantoms based on an epoxy resin with fillers—were made to study the influence of porosity and mineral content on ultrasound velocity and attenuation. The pores were simulated by 1 mm³ particles of a soft rubber, while the mineral content was imitated by a mineral residue of natural bone obtained by burning and grinding. The porosity and mineral content were varied in the range of 0–70% by volume with a step of 10%. The velocity, attenuation, and prevalent frequency of ultrasound were measured by the pulse transition method, using transducers with nominal frequencies 0.1, 0.2, 0.5, and 1.0 MHz. It was experimentally found that the ultrasound velocity decreased nearly exponentially with growth in porosity, while the velocity dispersion was negligible at frequencies >0.2 MHz; the ultrasound attenuation increased linearly with growth in porosity and strongly depended on the frequency; the velocity increased nonlinearly with growth in mineral content above 40%; the attenuation did not exhibit a distinct dependence on the mineral content; the porosity provoked a shift in the prevalent frequency of transducers, tending to the common value of 0.2 MHz, while the mineral content did not excite similar changes. The complex measurement of velocity, frequency-dependent attenvation, and prevenlent frequency of ultrasound is proposed in ultrasonic diagnostics of bone for more precise determination of the influence of the porosity and the degree of mineralization on the bone condition.Published in Mekhanika Kompozitnykh Materialov, Vol. 35, No. 2, pp. 211–220, March–April, 1999.     

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.     

Effect of force fields on a thermotropic liquid-crystalline copolymer of hydroxybenzoic acid and ethylene terephthalate. 1. Creation of oriented copolymer structure in a uniform magnetic field

A melt of a copolymer of 60% hydroxybenzoic acid and 40% ethylene terephthalate was subjected to a uniform magnetic field with B = 0.65 T at 300 °C. The structure and thermal expansion of the material was studied by x-ray diffraction and dilatometry. The magnetic field produced a highly oriented structure. Dilatometry revealed previously unreported relaxation transitions in this material.Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 2, pp. 269–281, March–April, 1995.     

Two-stage biaxial orientation of polypropylene film

The microstructure of polypropylene film at various points of the two-stage orientation process is described. It is shown that the supermolecular structures and film properties vary with the method of orientation. A proposed mechanism of two-stage biaxial film orientation is based on the experimental results.Moscow M. V. Lomonosov Institute of Fine Chemical Technology. Translated from Mekhanika Polimerov, No. 4, pp. 735–737, July–August, 1969.     

Reversibility of the orientation effect in linear polymers

It is established that the orientation effect in polymethylmethacrylate, assessed from the alteration in its properties, does not completely vanish after stabilization of the volume of the polymer during heating. A comparative evaluation of the physicomechanical properties in the unoriented, oriented, and oriented-and-restored states of the polymer indicates that some traces of orientation are retained.Lenin Kom somol Riga Institute of Civil-Aviation Engineers. Translated from Mekhanika Polimerov, No. 5, pp. 830–834, September–October, 1973.     

Two-dimensional extension of polyethylene and polypropylene film

The two-dimensional extension of polyethylene and polypropylene film has been investigated by optical microscopy. It has been established that there is no two-dimensional plastic flow (two-dimensional necking) and that failure is quasi-brittle in character. In a small region near the cracks that develop, uniaxial orientation of the polymer associated with stress concentrations near the crack tip is observed. Measurements show that the ultimate stress in two-dimensional extension is close to the necking stress in uniaxial tension.Mekhanika Polimerov, Vol. 3, No. 1, pp. 41–45, 1967