A. S. Kechek’yan

The structure and properties of polymer composite fibers based on poly(vinyl alcohol) and nanodiamond of detonation synthesis

The structure and properties of the oriented poly(vinyl alcohol) fibers modified with nanodiamonds (NDs) and nanodiamond soot (NS) of detonation synthesis were investigated by wide-angle and small-angle X-ray scattering methods, as well as by electron microscopy and mechanical testing methods. It was shown that the introduced nanodiamond soot particles were dispersed within the polymer matrix while maintaining a high dispersion level without aggregation. The NS treated with ultrasound was found to be a more effective modifier of the mechanical properties of the oriented fibers than untreated soot and NDs. The maximum increase in the longitudinal elastic modulus over nonmodified fibers (from 30 GPa up to 45 GPa) and in the energy stored by oriented fiber modified with NS upon breaking (from 3 up to 6 J/g) was obtained at a small (1% by volume) soot content, which is technologically attractive. The values of the adhesive strength of the soot modified with ND (1%) with volume poly(vinyl alcohol) fibers in the epoxy matrix were measured, and the maximally achieved value (42 MPa) was higher than the adhesive strength of the nonmodified fibers and comparable with the value of the reference sample (steel wire (57 MPa)).

Nanocomposites based on modified chitosan and titanium oxide

The effect of primary amino groups and molecular mass of chitosan on the stability of suspensions based on nanoscale TiO2 dispersions in acidic solutions of various concentrations at pH 2.5 was studied. In the case of chitosan prepared according to a commercialized process, the stability of TiO2 suspensions was low and depended on the concentration of the polymer solution. Solutions of low-molecular-mass highly deacetylated chitosan prepared by solid-phase synthesis stabilized a dispersion of nanosized TiO2 particles for a very long time. Nanocomposites based on a chitosan-PVA graft copolymer and TiO2 were prepared, in which the initial filler dispersion is retained up to very high filling ratios. A potential use of these nanocomposites in photocatalytic processes is discussed. The results of this study can be used for refining engineering procedures and processes for the manufacture of new biocompatible, bioactive, and biodegradable functional composite materials based on chitosan and synthetic polymers.

Structure of oriented fibers based on poly(vinyl alcohol) modified by detonation nanodiamonds

A comparative study of the structure and mechanical and thermal characteristics of nanocomposite oriented fibers based on poly(vinyl alcohol) impregnated with the nanodiamonds prepared by detonation synthesis and fibers based on the initial unmodified polymer has been performed. The conditions and regimes of gel spinning of the nanocomposite fibers containing highly dispersed nanosized filler without its aggregation are defined. The introduction of nanosized filler particles up to 7 vol % is found to entail no marked changes in the temperature intervals of glass transition and melting in the corresponding DSC thermograms. In this case, the amorphous-crystalline structure of the matrix polymer likewise remains practically unchanged. Under the selected conditions of gel spinning, the resultant nanocomposite fibers with comparable draw ratios are characterized by a higher longitudinal elastic modulus, close values of breaking strength, and lower values of elongation at break as compared with those observed for the fibers based on the initial unmodified polymer. The nanomodified fibers show promise as reinforcing elements in construction materials for various purposes.

Hybrid nanocomposites based on graft copolymer of chitosan with poly(vinyl alcohol) and titanium oxide

The physical-mechanical and relaxation properties of nanocomposites based on chitosan graft copolymers with poly(vinyl alcohol) and nanodispersed titanium oxide, where a high dispersity of the initial nanofillers was retained until high loading, were studied. The stabilization of the molecular mobility within the temperature range of 60 to 230°C was revealed in the copolymers of chitosan with poly(vinyl alcohol) upon loading with nanodispersed titanium oxide; this may be useful for changing the transport properties of the modified matrix. The obtained results are significant for the technological development of biocompatible and biodegradable composite materials based on chitosan and synthetic polymers for wide application.

Structural approach to the study of deformation mechanism of amorphous polymers

A new microscopic procedure for the visualization of structural rearrangements in amorphous polymers during their deformation to high strains is described. This approach involves the deposition of thin (several nanometers) metallic coatings onto the surface of the deformed polymer. Subsequent deformation entails the formation of a relief in the deposited coating that can be studied by direct microscopic methods. The above phenomenon of relief formation provides information concerning the deformation mechanism of the polymer support. Experimental data obtained with the use of this procedure are reported, and this evidence allows analysis of the specific features of structural rearrangements during deformation of the amorphous polymer at temperatures above and below its glass transition temperature under the conditions of plane compression and stretching, uniaxial tensile drawing and shrinkage, rolling, and environmental crazing. This direct structural approach originally justified in the works by Academician V.A. Kargin appears to be highly efficient for the study of amorphous polymer systems.

The structure and properties of polymer-nanodiamond composites on the base of block-copolymer polystyrene-polybutedien-polystyrene

The structure and mechanical properties of polymer-nanodiamond composites based on block-copolymer polystyrene-polybutadiene-polystyrene have been studied. It is revealed that, if either the nanodiamonds produced by detonation synthesis or the nanodiamond soot are introduced into block-copolymer thermoelastoplastic, the mechanical performances of the modified polymer matrix change significantly. It is shown that the optimal content (according to the modifying effect) of the nanodiamond soot in polymer composite is about 8–10% by weight. It is found that the spatial distribution of nanodiamond particles in the polymeric matrix of thermoelastoplastic is determinative in modifying the properties of polymeric nanocomposite. Ways to use the examined polymer-nanodiamond composites are discussed. The obtained results are important for the technological development of modified large-scale polymers, high-strength adhesives, glues and molten adhesives, and impact-resistant plastics.

Heating of polymers during neck propagation

The heating of polyethylene terephthalate, polyamide-66, and polyamide-6 during tensile drawing at room temperature was studied theoretically and experimentally. At a low draw rate, the necking temperature was close to the temperature of the surrounding air. An increase in the rate results in the transition to the adiabatic conditions of drawing. A necking temperature of 140°C was experimentally recorded in polyethylene terephthalate at a draw rate of 1000 mm/min and during the approach to the adiabatic conditions of drawing. A formula describing the dependence of the necking temperature on the draw rate was derived. The resulting value agreed fairly well with the theoretical estimation of the temperature. The drawing (strain) ratio in the neck and the draw stress are the crucial parameters determining the temperature. The rate of the transition to the adiabatic conditions of drawing was determined. The temperatures of adiabatic heating for various polymers were calculated. The increases in the temperatures of polycarbonate and low- and high-density polyethylene are relatively low. The increases in temperature can be regarded as moderate for polypropylene and polyvinyl chloride, while they attain the highest values in polyamide-6 and polyethylene terephthalate owing to the high draw ratios in the neck and the high draw-stress values.

Strengthened electrically conductive composite materials based on ultra-high-molecular-weight polyethylene reactor powder and nanosized carbon fillers

Electrically conducting samples of polymer composites of different compositions based on the reactor powder of ultra-high-molecular-weight polyethylene (UHMWPE) with a special morphology filled with fine powders of graphite, carbon nanotubes (CNTs), and electrically conducting carbon black (CB) are investigated. Strengthened oriented electrically conductive polymer composites possessing high tensile strength and conductivity values are obtained by the compaction of mechanical mixtures of the polymer and fillers powders, followed by the uniaxial deformation of materials under homogeneous shear conditions. Changes in the electrical conductivity of oriented composite materials during reversible “tension-contraction” cycles along the orientation axis direction are studied. The influence of the type of nanosized carbon filler on the electrical conductivity and mechanical properties of strengthened conductive composites oriented under homogeneous shear conditions is investigated.

Effect of a detonation-synthesized nanodiamond powder on the adhesive strength of a polymer fiber to an epoxy binder

In this work, we showed that the adhesive strength of oriented polyvinyl alcohol (PVA) fibers in an epoxy binder can be significantly improved by simulta neously modifying the polymer fiber and the polymer matrix by fine particles of detonation synthesized nanodiamond powder with oppositely charged sur faces. The finely divided binder in this work was detona tion synthesized nanodiamond powder (NP), which is an efficient modifier of the set of physicomechanical properties of polymer composites of new type [1, 2]. NP of two types were tested: standard detonation synthesized nanodiamond powder NP1 (Elek trokhimpribor, Lesnoi, Russia) and its modified ana logue NP2 produced at the Tekhnolog Special Design Engineering Bureau (St. Petersburg, Russia) by mild treatment of the standard NP in acid [3]. One of the components of the binder was chosen to be ED 20 epoxy resin:

The effect of orientation on the mechanism of deformation of polymers

The mechanical behavior of HDPE, medium-density PE, and amorphous and amorphous-crystalline PET after their preliminary orientation is studied. The polymers are oriented by rolling at room temperature on lab-scale rolls, tensile drawing at temperatures somewhat higher than their glass-transition temperatures, and extrusion at room temperature. At low degrees of rolling (below 1.5), the tensile yield stress does not actually increase. (In amorphous-crystalline PET, this parameter even decreases.) It seems that the absence of strain hardening at low draw ratios is a common feature of the behavior of polymers below their glass-transition temperatures. In contrast to the tensile yield stress, the engineering strength increases in proportion to the degree of rolling. A new procedure for construction of the dependence of true tensile yield stress on tensile strain is advanced. At low strains, the true tensile yield stress shows practically no increase. This conclusion is verified by theoretical calculations.