Investigation of the energy effects accompanying the elastic deformation of uniaxially oriented crystalline polymers

The energy (thermal and mechanical) effects accompanying the elastic deformation of uniaxially oriented crystalline polymers have been investigated; it has been established that, when these polymers are stretched, heat is released. It is shown that the heat release in uniaxial tension is a consequence of localization of the elastic deformation in the poorly ordered regions of the polymer. The relation between the thermoelasticity of uniaxially oriented crystalline polymers and their supermolecular structure is examined.Institute of Heteroorganic Compounds, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 785–798, September–October, 1970.     

Instability of the crystallites in oriented polymers under load

Large-angle x-ray diffraction and infrared spectroscopy have been used to investigate the behavior of the crystalline zones in oriented polymers under load. It is shown that under the influence of a load applied along the axis of orientation the crystallites are partially destroyed, the more so the greater the applied stress. For different polymers the destruction of the crystallites is the greater the weaker the intermolecular bonds. The stability of the crystallites is improved by orientation.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 516–520, May–June, 1976.     

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.     

Mechanism of the increase in strength and heat resistance of oriented polymeric materials modified by graft copolymerization with vinyl monomers

The mechanical properties and structures of oriented films and fibers composed of polyethylene, polymethyl methacrylate, and other amorphous and crystalline polymers modified by the synthesis of uniformly distributed graft and block copolymers of methyl methacrylate, acrylonitrile, vinylidene chloride and other monomers have been the subject of a comparative investigation. The effect of the grafted polymers on the molecular mobility, relaxation processes, and solubility of the materials is explained by reference to a universal physical "crosslinking" mechanism. A theory of the interrelation between the structure and physical properties of the materials, the nature of the polymers, and the grafting conditions is developed and used to analyze the experimental data on a broad range of systems.V. I. Lenin Belorussian State University, Minsk. Translated from Mekhanika Polimerov, No. 6, pp. 968–975, November–December, 1973.     

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     

Effect of submicroscopic crack formation and relaxation phenomena in polymers

The development of submicrocracks and the changes taking place in their concentration during loading and unloading cycles were studied by the low-angle x-ray scattering method in oriented amorphous-crystalline polymers (capron and polypropylene). The deformation () of the polymers was compared with the changes in submicrocrack concentration (N_cr).A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 387–392, May–June, 1970.     

Behavior of the supermolecular structure of oriented amorphous-crystalline polymers under cyclic loading

Equipment has been developed for investigating small-angle X-ray diffraction in various phases of the loading period in cyclically extended polymers. The behavior of the large-period structure of oriented polycaprolactam (kapron) films in cyclic extension has been studied. The results are compared with the data on the behavior of the same structure in static tests.Mekhanika Polimerov, Vol. 4, No. 2, pp. 195–199, 1968     

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.     

Intensity of the relaxation processes in statically loaded,highly oriented synthetic fibers

An experimental study of the stress relaxation and creep of a series of synthetic fibers has revealed a reduction in the intensity of these processes as the tensile strain increases. On the basis of a comparison of the relations obtained and the results of previous studies of loaded oriented polymers using small-angle x-ray scattering and NMR techniques it is suggested that the observed effect is attributable to orientational ordering of the through macromolecules in the amorphous regions of the fiber. It is also concluded that in oriented polymers at strains considerably below breaking values the elementary relaxation events are physical (and not mechanochemical) in nature.Kirov Leningrad Institute of the Textile and Light Industries. Translated from Mekhanika Polimerov, No. 1, pp. 154–157, January–February, 1973.     

Relation between fracture and deformation in oriented polymers

The development of submicroscopic cracking under load has been studied (by a small-angle X-ray scattering technique) in such oriented polymers as Kapron (Nylon 6), polypropylene, etc. The increase in crack density (N_cr) is compared with the variation of the tensile strain (). The observed correlation between and N_cr indicates that the processes of fracture and deformation of oriented polymers are closely connected. The presence of a similar correlation in loading-relaxation-repeat loading experiments establishes fracture as the primary process.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 43–47, January–February, 1970.     

Effect of the conditions of bond formation and destruction on the adhesion of polymers to synthetic fibers

It is shown that the adhesion of linear polymers can be measured by shearing a monofilament relative to a microblock of adhesive [1]. Experiments have been performed on polypropylene, polyethylene terephthaliate, polycaprolactam, polyvinyl alcohol, and glass fibers. Broad variation of the diameter, structure, and physicomechanical properties of the various kinds of oriented fibers had practically no effect on the adhesion. The physicochemical properties of the adhesive solutions at the moment of application to the fiber likewise do not affect the adhesion which, other things being equal, is determined by the nature and supermolecular structure of the polymers in the contact zone.Belorussian Lenin State University, Minsk. Branch of the Karpov Scientific-Research Physicochemical Institute, Obninsk. Translated from Mekhanika Polimerov, No. 6, pp. 1042–1048, November–December, 1970.     

Thermomechanical behavior of liquid-crystal polyesters

We have used the thermomechanical method to investigate the processes of self-elongation and shrinkage in uniaxially oriented liquid-crystal (LC) polyesters (CPET — the copolyester of terephthalic acid, phenylhydroquinone, and p-hydroxybenzoic acid; Ultrax — the copolyester of terephthalic acid, isophthalic acid, and bisphenol) and the injection-molded copolyester of hydroxybenzoic and hydroxynaphthoic acids Vectra A900. A universal tensile tester and a thermomechanical tester were used for the investigations. We studied the deformation behavior for the first and second heating under negligible applied stress. We prepared CPET samples in the form of as-spun and annealed fibers, Vectra samples in the form of cubes cut from the nonoriented part of the molded piece (VI) and from the longitudinally oriented central part (VII), Ultrax samples in the form of strands (noncrystalline UI and crystalline UII). We observed a permanent length increase for the as-spun CPET (Fig. 1) and shrinkage in the glass-transition region for the annealed CPET (Fig. 2) for the first and second heating. Note that the as-spun CPET is a smectic polymer, and the annealed CPET contains smectic and crystalline phases. The thermomechanical curves of VI seem to be typical of any molded polymer (Fig. 3). In contrast, for the oriented VII we see spontaneous elongation upon heating in the direction of orientation, with pronounced transverse shrinkage (Fig. 4). The length increase for the noncrystalline UI is quite considerable for the first heating. We observed both spontaneous elongation below the glass-transition temperature and subsequent shrinkage for crystalline UII for the first heating. All the Ultrax curves are much smoother for the second heating (Fig. 5). Spontaneous elongation upon heating appears to be a characteristic feature of oriented LC polymers, the polymer being either fully oriented or oriented within some part of the sample. Shrinkage of LC polyesters upon heating is also possible, as a result of both processing factors and crystallinity. There are two types of restructurization processes: orientation and crystallization (possible for LC polymers capable of forming a crystalline phase).A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 32, No. 1, pp. 98–105, January–February, 1996.     

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     

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.     

On the friction mechanism of polymers with surface-active lubricants

Questions relating to the friction mechanism of polymers with boundary lubrication are discussed. A hypothesis is proposed according to which the molecules of surface-active compounds are oriented by static electricity. A method of verifying this hypothesis is described.Mekhanika polimerov, Vol. 1, No. 1, pp. 128–135, 1965     

Changes in the structure of polymeric materials in a magnetic field

It is shown that the action of a magnetic field leads to a change in the supermolecular structure of crystalline polymers. The creation of an oriented state in amorphous thermoplastics and thermosets is accompanied by an increase in their hardness and the homogeneity of the structural state.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 737–739, July–August, 1973.     

Some laws of the elastic properties of oriented fibrous polymers and fibers

The author considers the results of calculations of the limiting values of the elastic properties (modulus of elasticity and load-extension diagram) of the main types of chemical fibers, using a model with "ideal orientation" of the molecules and the derived laws of deformation of polymer chains. A method is proposed for calculating the elastic properties of "ideally oriented" polymers from the velocity of propagation of an elastic deformation pulse and the effective density of the "skeletons" of the polymer chains. Values of the moduli of elasticity of the amorphous regions of the structure of oriented polymers are calculated. The calculated results are compared with experimental data on the elastic properties of fibers.Mekhanika Polimerov, Vol. 2, No. 1, pp. 34–42, 1966Paper read at the XIV All-Union Conference on High-Molecular Compounds, Oriented State.     

Acoustic-optical criteria of analysis of orientation ordering in some fiber forming polymers

Conclusions A correlation was established between the scalar field describing the ordering of the structure and the tensor field characterizing the elastic constants of a material. It was proved that it is possible to use the acoustic and optical criteria for the analysis of the structure of some oriented fiber forming polymers. It was shown that the correlation between the suggested acoustic criteria can be used for optimizing the process of orienting drawing.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 771–775, September–October, 1986.     

Fractographic study of macrocrack propagation in oriented Kapron

The fracture surface of an oriented Kapron monofilament has been studied at electron-microscope and optical magnifications with the object of establishing the details of the micromechanism of crack propagation associated with the fracture of polymeric materials. Microparabolic figures can be observed in the specular zone of the fracture surface. This relief may be assumed to originate in the interaction of the main crack and the submicroscopic cracks present in loaded polymers. In the region of high main-crack velocities it is possible to observe a self-oscillatory motion of the tip of the main crack leading to the formation on the fracture surface of a system of bands parallel to the main crack front.Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 4, pp. 645–648, July–August, 1971.     

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