The theory of orientational drawing of linear amorphous polymers

On the basis of modern ideas on the structure of linear, amorphous polymers a model of a molecular, three-dimensional network with temporary cross-links and van der Waals interaction between the chains is presented. Using this model as a starting point, a differential equation for the deformation of a linear, amorphous polymer in the viscoelastic state is derived. The differential equation for the orientation of a linear, amorphous polymer, which describes the evolution of distribution functions for statistical segments, is obtained. Previously obtained results follow from this theory as special cases.V. I. Lenin State Pedagogic Institute, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1021–1028, November–December, 1974.     

Stress relaxation in glassy polymers

Stress relaxation in amorphous linear polymers has been investigated below the glass transition point at various strain rates, temperatures, and strains. A model of a nonlinear viscoelastic body is proposed as a means of describing the effect. It is shown that stress relaxation is well described by the model considered and is correlated with the deformation characteristics of the polymers.A. F. Ioffe Physico-Technical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 987–994, November–December, 1971.     

Fatigue strength and structure changes of polyethylene-oxide films under static and cyclic loading

Conclusions The behavior of the PEO films under long-term loadings show certain special features reflected mainly in the unusual form of the fatigue curve and the presence of three types of creep curves. The most significant factors affecting the fatigue characteristics of the PEO films are the molecular mass and the degree of crystallinity — when these factors increase the fatigue resistance also usually increases. To evaluate suitability of PEO films for service it is promising to use the cyclic bending test. This loading mode characteristic of practice makes it possible to carry out tests at low strain levels and cumulate considerable damage. Examination by the x ray diffraction method showed that in cyclically bent PEO films not only the amorphous but also crystalline structures are damaged.Translated from Mekhanika Kompozitnykh Materialov, Vol. 3, No. 3, pp. 404–412, May–June, 1994.     

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.     

Relaxation processes in oriented amorphous polymers

Values of the birefringence and high-elastic strain are presented for amorphous polystyrene subjected to stretching and annealing. The laws of the relaxation processes that occur in linear polymers under these conditions are discussed.Mekhanika Polimerov, Vol. 2, No. 3, pp. 323–329, 1966     

Strengthening of Polypropylene Strips by Orientational Stretching in Liquids

Data on the orientational stretching of polypropylene strips in process liquids serving as plasticizers of polypropylene are presented. Such a stretching allows one to avoid many complications characteristic of stretching in air and to increase the maximum stretch ratio significantly (up to 15). The stretching of strips is accompanied by changes in the crystalline structure of polypropylene and by transformation of the amorphous phase into a crystalline one. It is established that the specific strength of the orientationally stretched strips as a function of stretch ratio has a maximum. This is caused by the competing processes of macromolecule orientation in the stretching direction and the destruction of molecular bonds, which leads to the origination of microdamages in the strip surface layer and to a growing content of amorphous phase. It is shown that the extraction of process liquids from the stretched strips increases their specific strength by 20–30%.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 251–264, March–April, 2005.     

Mechanical relaxation processes in polymers

The various kinetic processes are classified and the place of relaxation effects among them is established. The theoretical basis of mechanical relaxation phenomena in polymers is outlined. The characteristics of relaxation processes associated with molecular mobility are examined with reference to various classes of polymers, in particular, amorphous and crystalline polymers, copolymers, and mechanical mixtures. The characteristics of relaxation processes associated with rearrangement of the supermolecular structures in amorphous and crystalline polymers are considered.This article is a review of mechanical relaxation effects in polymers with particular attention to research conducted in the Problem Laboratory of Polymer Physics of the Moscow Lenin State Pedagogical Institute.Problem Laboratory of Polymer Physics, Lenin Moscow State Pedagogical Institute. Translated from Mekhanika Polimerov, Vol. 5, No. 1, pp. 30–53, January–February, 1969.     

On the theory of infrared dichroism of oriented amorphous polymers

A network model of a linear amorphous polymer is used as a basis for calculating the infrared dichroism of uniaxially and biaxially oriented material. The dependence of the dichroism on the uniaxial and biaxial stretch ratios, orientation temperature, and certain other factors is investigated. Previously published experimental data are discussed.Moscow Lenin State Pedagogical Institute, Problem Laboratory of Polymer Physics. Translated from Mekhanika Polimerov, No. 6, pp. 979–984, November–December, 1970.     

Predicting the Deformability of Expanded Polystyrene in Short-Term Compression

A regressive model is presented for the relationship between the compressive stress and strain of expanded polystyrene (EPS) on a 0–35% strain range. On the whole, the model agrees well with experimental data. A practical way is suggested for determining the coefficients of the model from the known density of EPS plates and their compressive stress at a 10% strain. The model allows one to predict the critical compressive stress and the elastic modulus of EPS.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 157–162, March–April, 2005.     

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.     

Relaxation processes in oriented amorphous and crystalline polymers

Studies were made of the experimental data on the relaxation processes leading to the preferential molecular disorientation and uniaxially drawn amorphous and crystalline polymers.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 787–792, September–October, 1972.     

Quasistatic anti-plane motion in the simplest theory of nonlinear viscoelasticity

We consider a very simple model in the framework of differential viscoelastic materials which are isotropic and incompressible. In this model the Cauchy stress tensor is split in an elastic part and a dissipative part. The elastic part is derived from a strain-energy density function only of the first invariant of the Cauchy–Green strain tensor. The dissipative part is like the Navier–Stokes equations: linear in the stretching tensor with a constant viscosity parameter. For this model we provide some time and spatial estimates in the quasistatic approximations for the equations governing anti-plane shear motions. Several explicit examples for specific form of the strain energy are produced. Our results impose analytical restrictions on the mathematical properties of the strain energy to ensure a physical behavior in the creep and recovery experiments. Moreover, we show polynomial decay for the spatial behavior in the class of stress-hardening (or strain-stiffening) materials. For stress-softening materials a Phragmen–Lindelof alternative is proved.     

Molecular destruction of polymers at the apex of a major crack

We employed infrared spectroscopy and infrared spectroscopy of deflected total internal reflection to study the rupture of polymer macromolecular chains (polyethylene and polypropylene) at the apex of a growing crack. It was shown that the break concentration at the crack surface is of the same order of magnitude as the total concentration of chemical bonds in the polymer; molecular rupture occurs not only at the apex itself but also at some distance from it. The dependence of the break concentration on the distance from the crack apex was measured. The observed patterns were related to the experimentally determined external-load distribution function for individual chemical bonds near the crack apex.I. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 4, pp. 621–625, July–August, 1972.     

An infrared spectroscopic study of the breakdown of polymers under load

It has been found that when a uniaxial tension is applied to highly oriented polymer films of polypropylene, polyvinyl alcohol, or polyethylene, an increase in the intensity of the absorption bands corresponding to the vibrations of the C=O carbonyl groups is observed. These groups are produced by the oxidation of the free radicals formed on the rupture of the chemical bonds under the influence of mechanical stress. The composition of the products has been studied, and their concentration has been estimated. Curves giving the accumulation of C=O groups with time at constant load and with increase in stress for a fixed period of time under load have been studied. It is suggested that the rate of accumulation of C=O groups in both cases is determined chiefly by the rate of rupture of the molecular chains under load.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 433–436, May–June 1970.     

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.     

Relation between the mechanical properties of polymers and the kinetic flexibility of the macromolecules

Nuclear magnetic resonance combined with extension of the specimens in the NMR spectrometer on the reversible deformation range has been used to study the cooperative modes of motion of the macromolecules in polymers, specifically polycaprolactam and polyethylene terephthalate. For each of these polymers there are two temperatures near which the nature of the molecular motion changes sharply. At low temperatures there is a transition from independent hindered vibrations of the repeating units to correlated vibrations, as a result of which the chains in the amorphous regions acquire limited kinetic flexibility within the glassy state; at high temperatures there is a transition to segmental motion. The question of how changes in the modes of molecular motion are reflected in the macroscopic mechanical properties of polymers is examined.Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 24–29, January–February, 1971.     

Viscoelastic behavior of deformed polytetrafluoroethylene

The effect of pressure and heat treatment on the viscoelastic properties of polytetrafluoroethylene has been studied by the free torsional vibration method. It is shown that the deformation of PTFE produces an important change in the principal relaxation processes associated with the molecular mobility in the amorphous regions. On the basis of the measurements made it is concluded that the mechanical strength of the PTFE increases, which is in good agreement with the results of static tests. A conclusion is drawn concerning the molecular mechanism of the processes associated with the deformation of PTFE.Scientific-Research Institute of Plastics, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 943–945, September–October, 1974.     

Mechanics of the static tension of a through chain in amorphous crystalline polymers

The displacements and tensions of the points on a through chain lying inside one crystallite of an oriented amorphous crystalline polymer are analyzed theoretically for various degrees of withdrawal of the chain from the crystallite. The tension of the chain in the amorphous region is examined as a function of its contour length and the length of the amorphous region. The nature and efficiency of the stoppers (obstacles) retaining the through chain inside the crystallites are considered. Specific results are calculated for polyethylene and polypropylene.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 771–778, September–October, 1973.     

Strength properties of oriented amorphous linear polymers in relation to their structure

Tensile tests have been conducted at room temperature on uniaxially oriented films of a number of amorphous linear polymers. It has been shown that the mechanical properties of the oriented polymers in the glassy state are chiefly determined by two parameters of the structure—the degree of orientation of the macromolecule segments and the concentration of stressed chains per unit volume, irrespective of the molecular weight of the polymer and the orientational stretching conditions.Mekhanika Polimerov, Vol. 3, No. 3, pp. 455–460, 1967     

Calculation of the rupture life of mechanical rubber goods

The stress-strain relation for an aging material is obtained from an analysis of a four-element model of a viscoelastic body with variable coefficients. In this formulation the problem of calculating the rupture life is divided into four steps: a) solution of the boundary-value problem of the theory of elasticity of an incompressible material; b) calculation of the stationary thermal field; c) solution of the rheological equation at the danger point; d) solution of the criterial equation for the local fracture time. An example of the calculation of the high-temperature rupture life of a rubber cord under constant load is given. The agreement with experiment is satisfactory.Riga Polytechnic Institute. Translated from Mekhanika Polimerov, No. 1, pp. 91–95, January–February, 1976.