G. K. Elyashevich

Thermochemical and deformational stability of microporous polyethylene films with polyaniline layer

Thermostability and structure transformations upon heating of composite systems consisting of a microporous polyethylene film and a conducting polyaniline (PANI) layer have been investigated by thermogravimetry (TG), differential thermal analysis (DTA), differential scanning calorimetry (DSC), and wide-angle X-ray scattering (WAXS). Microporous polyethylene films were prepared by melt extrusion with subsequent annealing, uniaxial extension, and thermofixation. Polyaniline layers were formed by polymerizing aniline from solution in situ or by deposition of colloidal polyaniline dispersion on the polyethylene film surface. Composite systems have been found to demonstrate a considerably lower shrinkage upon heating than microporous polyethylene substrates. It has been discovered from DTA, DSC, and WAXS data that oriented phases in the polyethylene melt are formed in composite systems at melting temperature of polyethylene support. Oriented state in polyethylene melt is maintained at heating of composite samples up to the temperatures exceeding polyethylene melting point at several tens degrees.

Synthesis and characterization of thin polypyrrole layers on polyethylene microporous films

Abstract The paper describes the synthesis and properties of polypyrrole (PPyr) layers, obtained by gas-phase oxidative polymerization, on the surface of a microporous polyethylene (PE) film. Kinetic studies have revealed three stages in the pyrrole polymerization in situ on the PE film. Properties of the composite with various contents of PPyr have been investigated by ultrafiltration, gas separation, and electrodialysis techniques. The composite containing up to 12% of PPyr is an ultrafiltration membrane permeable to liquids. The electrolytic resistance of the HCl-doped PE–PPyr composite anion-exchange membranes has been measured with direct and alternating current as a function of the polypyrrole content. Electron-microscopic and mechanical characteristics of the PE films and composite membranes have been determined.

Structure development in oriented polyethylene films and microporous membranes as monitored by sound propagation

Microporous membranes of high-density polyethylene were prepared by melt-extrusion followed by annealing and uniaxial extension. Crystallization at a high melt flow rate and subsequent annealing of the spun films with fixed ends led to the formation of oriented hard-elastic materials with a high modulus of elasticity and a considerable work recovery. Uniaxial stretching of such systems along the orientation direction induced the formation of microscopic pores due to the specific structure of the hard-elastic material. At some critical values of the processing parameters, throughflow channels were formed, converting the film into a microporous membrane permeable to liquids and vapors. Sound propagation, tensile measurements, and X-ray diffraction techniques were used to characterize the structure and properties of the samples at individual stages of the process as a function of the processing parameters. In particular, it was shown that polar diagrams of the sound propagation velocity reflect sensitively the structural changes in the process of porous structure formation.

Electrical resistance and diffusion permeability of microporous polyethylene membranes modified with polypyrrole and polyaniline in solutions of electrolytes

Composite systems based on a microporous polyethylene (PE) membrane modified with conducting polymers such as polypyrrole (PPy) and polyaniline (PANI) have been elaborated. Conducting polymers were deposited onto PE membranes in situ during the oxidative polymerization of pyrrole from gas phase or by the polymerization of aniline in aqueous medium. Composite membranes have a low resistance in electrolyte solutions owing to the coating with conducting polymers inside the pores. The dependence of electrical resistance of modified membranes on concentration of hydrochloric acid or sodium hydroxide solutions, in which the conducting polymers are in protonated or non-protonated states, respectively, was studied using alternating and direct electric currents. Diffusion permeability of composite membranes to acid, salt and alkali solutions has been also studied.

Swelling-contraction of sodium polyacrylate hydrogels in media with various pH values

The swelling kinetics of sodium polyacrylate gels has been studied in media with different pH values. The pH dependence of the degree of equilibrium swelling shows a maximum at pH 6. The degree of swelling decreases with an increase in the crosslink density, and this dependence follows an S-shaped pattern for all examined gels. When a gel swollen in media with pH 3–13 is dried in air, its contraction is reversible, while in the case of the gel swollen in acidic media at pH < 3, the process is irreversible owing to the replacement of sodium ions with protons.

Electroactive hydrogels based on poly(acrylic acid) and polypyrrole

This study is concerned with the preparation of novel composite systems in which the hydrogel of crosslinked poly(acrylic acid) is a matrix and polypyrrole is an electroconducting component. The effects of synthesis conditions on the structure of the composite systems, their ability to swell in water, and mechanical characteristics are studied. The proposed synthesis procedure allows production of a bulk electroconducting phase of polypyrrole in the hydrogel matrix. The effect of crosslink density of hydrogel on the character of polypyrrole distribution in the matrix is studied. The above composites combine the electrical characteristics of polypyrrole with high elasticity and the ability to repeatedly swell the crosslinked poly(acrylic acid).

The effect of a polypyrrole coating on the thermal stability of microporous polyethylene membranes

Microporous polyethylene (PE) membranes were coated on both sides with a polypyrrole (PPy) overlayer. PPy was deposited also on the walls of pores. Thermodeformation measurements indicate that the hard framework produced by rigid-chain PPy controls the mechanical properties of composite membranes. FTIR spectroscopy was used to detect oxidative processes in both polymer components above 200 °C. Elemental analysis showed that the nitrogen content remains at high level, even after the treatment of membranes in air at 300 °C, indicating that the decomposition involved mainly PE while PPy was much more stable. The changes in surface relief after annealing were assessed with electron microscopy. No oxidative processes were identified in the FTIR spectra of composites after annealing in vacuum, even after treatment at 300 °C.

Properties of polymer conducting thin layers on the surface of microporous polyethylene films

Thin layers of conducting polymers were formed on the microporous polyethylene film containing through flow channels. The films are characterized by the relief-like strongly developed surface. The layers were obtained by polymerization in gas phase (polypyrrole) or in solution (polyaniline). Conducting layers were located on the film surface and on the walls of channels. Conductivities of layers along the film surface (sheet) and between the film surfaces (volume), and also electrolytical conductivity of samples have been measured. Thermodeformational behavior of the samples under study and porous polyethylene support has been investigated. The effect of conducting polymer layer on structure transformations upon heating has been studied by WAXS, thermogravimetry, DTA and DSC.

Orientation of pores in microporous polyethylene films as determined by polarized absorption spectroscopy

Abstract Microporous polyethylene films with good mechanical properties can be produced on the basis of hard-elastic specimens by uniaxial deformation. The so called ”guest-host” effect [1, 2] was explored to determine the order parameter of pores in a series of PE membranes so produced by polarized absorption spectroscopy using dichroic dyes dissolved in the nematic liquid crystal ZLI 1840 (LC) as indicator. The parameter of the orientation order SA of the pores along the draw direction was found to increase with increasing spin draw. A qualitative comparison of SA with the thermodynamic behavior of the dye + LC systems confined in the pores was made. The results obtained are related to the mechanism of porous structure formation.

Polymorphic transformations in poly(vinylidene fluoride) films during orientation

The effect of uniaxial orientational drawing and isometric annealing on the ratio of polymorphic modifications in the crystalline phase of poly(vinylidene fluoride) is studied. The role of drawing temperature and draw ratio in the structural rearrangements during polymer deformation is analyzed. The conditions providing the highest content of the polar crystalline phase in the polymer are determined. The mechanical properties of the films drawn at different temperatures are investigated.