E. M. Ivan’kova

Effect of single-walled carbon nanotubes and carbon nanofibers on the structure and mechanical properties of thermoplastic polyimide matrix films

The effects of additives of single-walled carbon nanotubes prepared via electric-arc synthesis and carbon nanofibers produced via gas-phase synthesis on the crystallization capacities and mechanical and electric properties of composite films of a thermoplastic polyimide (PI) matrix based on 1,3-bis-(3,3′, 4,4′-dicarboxyphenoxy)benzene and 4,4′-bis-(4-aminophenoxy)biphenyl after their uniaxial drawing and additional annealing are studied. The use of these fillers induces the heterogeneous nucleation of a crystalline phase of PI on the nanoparticle surface. A higher specific interface area in the case of addition of carbon nanotubes relative to that of carbon nanofibers leads to the formation of the crystalline structure of PI with a small crystallite size and high imperfection. Uniaxial drawing leads to the formation of a supermolecular structure that is optimum for crystallization during additional annealing and removes the kinetic hindrances to crystal growth. The properties of these fillers have a significant effect on the orientation of the nanoparticles and the matrix macromolecules during the uniaxial drawing of the films, which is accompanied by an increase in the elastic modulus with an increase in the draw ratio and the ability of the composite films to undergo orientational crystallization during additional annealing.

Composite materials based on chitosan and montmorillonite: Prospects for use as a matrix for cultivation of stem and regenerative cells

This work considers the structural and mechanical properties of composite materials based on chitosan, as well as montmorillonite micro- and nanoparticles and the possibility of using them for cultivation and targeted delivery of mesenchymal stem and regenerative cells. It has been shown that, upon addition of montmorillonite, the biomaterial acquires stability of structural and mechanical properties under conditions of sterilizational treatment and during manipulations in liquid media in the course of cell cultivation. With the aid of in vitro cultivation with the use of dermal fibroblasts and mesenchymal stem cells of adipose tissue, this material was shown to have a complex of properties providing matrix biocompatibility.

Distribution of zirconia nanoparticles in the matrix of poly(4,4′-oxydiphenylenepyromellitimide)

Poly(4,4′-oxydiphenylenepyromellitimide) is used as a polymer matrix for incorporation of zirconia nanoparticles with different compositions (ZrO2 and Y0.03Zr0.97O1.985), sizes (20 ± 5 and 10 ± 2 nm), and morphologies (spheres, hollow spheres, rods). The nanoparticles are incorporated during the synthesis of poly(amido acid), a prepolymer of polyimide, and ZrO2 nanoparticles are pretreated with organosilicon compounds (tetraethoxysilane, γ-aminopropyltriethoxysilane, and 3-(trimethoxysilyl)propyl methacrylate). The effect of surface modification of ZrO2 nanoparticles on their distribution in poly(4,4′-oxydiphenylenepyromellitimide), depending on the type of the organosilicon compound as well as on the dispersity, shape, and chemical composition of particles, is studied.

Features of the amorphous-crystalline structure of UHMWPE

To reveal the features of the structure of UHMWPE that depend on the catalytic system used for synthesis, a comparative study of the sets of laboratory and commercial powders of UHMWPE synthesized on different catalysts in the slurry process under different conditions is conducted. This study includes the use of various modern physical methods, such as transmission and scanning electron microscopy, X-ray analysis, Raman scattering spectroscopy, differential scanning calorimetry, nuclear magnetic resonance, and thermoluminescence. All nascent particles are shown to have a complex hierarchical structure. In all reactor powders, the elementary structural unit is crystalline lamellas, whose dimensions and mutual orientation are dependent on the type of catalytic system. In the synthesis on the supported catalysts, the character of the formed structure depends on the characteristics of the substrate. During the breakdown of the substrate in the course of the synthesis, fibrils form. The colloidal dimensions of the catalyst particles are responsible for a more uniform lamellar structure of the reactor powders. The conformational composition of the segments of molecules in the interlamellar regions of the reactor powders is characterized.

Nanoporous structure of ultrahigh-molecular-weight polyethylene reactor powder

The influence of the catalyst system and synthesis conditions on the morphology and molecular dynamics of reactor (nascent) powders of ultrahigh-molecular-weight PE synthesized over supported Ziegler-Natta catalysts in laboratory reactors was studied by means of electron microscopy and 1H broadline NMR spectroscopy. For comparison, commercial reactor powders were studied as well. The type of the catalyst system and the temperature of slurry polymerization have a substantial effect on the supermolecular structure of the nascent polymer. The proton NMR spectra of the reactor powders synthesized at low temperatures display a narrow component. An analysis of its behavior at low temperatures and different humidities led to the conclusion that the signal is due to water localized in nanopores of 2–4 nm in size in the nascent polymer. The role of nanopores in the sintering of reactor particles is discussed.

Surface structure of nascent particles of ultrahigh molecular weight poly(ethylene) reactor powders

A comparative investigation of the surface structure of three ultrahigh molecular weight poly(eth-ylene) (UHMWPE) reactor powders that differ by their ability to be processed to high-performance fibers is carried out with a JEOL 6300 scanning electron microscope and a nanoluminograph, which makes it possible to study thermoluminescence of ultrathin near-surface layers of solids. The activation energies of relaxation processes in near-surface layers of nascent particles and the sizes of kinetic units of motion, for which the mobility is defrozen in the temperature range of the corresponding transitions, are calculated from the glow curves. The possible location of kinetic units in supermolecular formations resolved in micrographs and their influence on the dissolution of the reactor powder are discussed.

Influence of spinning conditions on properties of chitosan fibers

Chitosan fibers were prepared by a coagulation method involving spinning from an acetic-acid solution (2%) of polymer (4%) in basic alcoholic solution. The influence of feed rate and shear rate of the polymer solution and the degree of orientational drawing on the structure and mechanical properties of the fibers were studied. The optimum spinning parameters were determined. The chitosan fibers had an anisotropic structure with the macromolecules oriented primarily along the fiber axis.

Tissue-Engineered Vascular Graft of Small Diameter Based on Electrospun Polylactide Microfibers

Tubular vascular grafts 1.1 mm in diameter based on poly(L-lactide) microfibers were obtained by electrospinning. X-ray diffraction and scanning electron microscopy data demonstrated that the samples treated at T = 70°C for 1 h in the fixed state on a cylindrical mandrel possessed dense fibrous structure; their degree of crystallinity was approximately 44%. Strength and deformation stability of these samples were higher than those of the native blood vessels; thus, it was possible to use them in tissue engineering as bioresorbable vascular grafts. The experiments on including implantation into rat abdominal aorta demonstrated that the obtained vascular grafts did not cause pathological reactions in the rats; in four weeks, inner side of the grafts became completely covered with endothelial cells, and fibroblasts grew throughout the wall. After exposure for 12 weeks, resorption of PLLA fibers started, and this process was completed in 64 weeks. Resorbed synthetic fibers were replaced by collagen and fibroblasts. At that time, the blood vessel was formed; its neointima and neoadventitia were close to those of the native vessel in structure and composition.

Supramolecular structure of chitin nanofibrils

The structure of chitin nanofibrils as a promising filler for bioresorbable suture materials and matrixes for cellular technologies and tissue engineering is investigated via the methods of X-ray diffraction and scanning electron microscopy. It is shown that the powder microparticles obtained via lyophilization of an aqueous dispersion of chitin nanofibrils have a band structure with a cross-sectional size of 30 μm and a thickness of 0.1 μm. The bands consist of nanoparticles 25 nm in thickness and 400–500 nm in length. The chitin nanofibrils are composed of two crystallites with cross-sectional sizes of 11–12 nm and b axes perpendicular to the nanofibril axis. The chitin nanofibrils tend to form planar elements with a layered structure on both the microlevel and the nanolevel. The addition of chitin nanofibrils to a chitosan solution leads to a rise in its viscosity. However, the action of shear stresses leads to a substantial decrease in the chitosan-chitin solution viscosity, a phenomenon that is due to the presence of planar anisodiametric nanoparticles of chitin.

Effect of montmorillonite on the structure and properties of powder epoxy compounds for polymeric coatings

Procedures for preparing nanomodified powder epoxy compounds with various concentrations of montmorillonite were examined. The dispersion of particles in the epoxy oligomers was studied by X-ray diffraction analysis and electron microscopy. The influence of the content of the modifiers on the physicomechanical properties of cured block specimens was analyzed.