Molecular Characteristics of Chitosan and Structure of its Films Formed from Water Solutions of Acetic and Hydrochloric Acids

Molecular characteristics of chitosan in diluted water solutions of acetic and hydrochloric acids were studied by viscometry, dynamic light scattering, and thin layer chromatography. Chitosan molecules were found to undergo destruction in the solutions of hydrochloric acid and its mixtures with acetic acid. The structure of the chitosan films cast from these solvents was studied by DSC, TGA, and SEM. As shown by electron microscopic data, all the films had an amorphous-crystalline structure but the films prepared from chitosan solutions in diluted hydrochloric acid were characterized by a higher degree of crystallinity. It was supposed that a lower molecular mass of chitosan molecules in the hydrochloric acid solutions results in more extended conformations providing a higher capability of self-organization and formation of regular supermolecular structure. The difference in crystal modification in structure of the films cast of these acids was observed. It was found that the films prepared from the mixtures of acids had a spherulite structure and the crystal modification like ones cast from hydrochloric acid, but with a lower degree of crystallinity

ELECTROMECHANICAL SYSTEMS BASED ON POLYMER HYDROGELS FOR MICRO-SCALE ACTUATORS

The paper proposes a novel approach to the construction of actuators for automation and robotics based on the use of new electroactive polymer materials – swelling hydrogels. The hydrogel pH-sensitive materials containing two polymer components, crosslinked polyacrylic acid and polyvinyl alcohol, are obtained. A procedure for the synthesis of hybrid hydrogel is described, and the achieved values of their characteristics, degrees of swelling in water and water solution of salt, are given. A method of hydrogel elements preparation with a specified geometric configuration was developed, and cylindrical and also ring-shaped samples were prepared. Mechanical properties of the prepared hydrogels at compression were measured. It is shown that the hybrid hydrogels exhibit higher strength and elasticity than the one-component polyacrylic acid hydrogels obtained by the same method. An actuator design is proposed with a hydrogel as a controlled element. An experimental layout of such actuator was constructed. The stability of material characteristics was determined, and methods for the electrodes fixation and electric current supply were developed. It was found that ring-shaped samples of hydrogels demonstrate electromechanical response – compression when electric current passes through their cross section. This fact was the evidence that these hydrogels can be used as a linearly operating generator of mechanical force. It is shown that this effect is more pronounced for samples swollen in water solution of sodium sulfate rather than in distilled water

ETANERCEPT IN THE REAL CLINICAL PRACTICE OF TREATMENT IN PATIENTS WITH ACTIVE JUVENILE IDIOPATHIC ARTHRITIS

The paper presents the results of an open-label nonrandomized prospective trial, the purpose of which was to evaluate the efficiency and safety of etanercept (ETC) treatment for different forms and variants of active juvenile idiopathic arthritis (JIA) in real clinical practice. The trial included 24 patients with JIA. ETC treatment proved to be effective in most patients with a long disease history and a high clinical and laboratory activity who were refractory to conventional antirheumatic therapy. ETC therapy was most effective in patients with the articular form of the disease who showed 100% improvement in at least ACRpedi30 criteria at 6 months of treatment

Orientational crystallization and orientational drawing as strengthening methods for polyethylene

This paper reports on the theoretical and experimental studies of structure formation and strengthening (stiffening) of flexible-chain polymers. Two techniques of strengthening relying on the melt extrusion, i.e. orientational crystallization (crystallization initiated by melt extension) and drawing (uniaxial stretching of a crystallized polymer) are analysed by theory. The experiments involved preparation and study of melt extruded films and film fibers of linear polyethylene formed by the two techniques mentioned above. The effect of the degree of orientation and other parameters of the formation processes on the mechanical characteristics and the factors limiting the ultimate values of these characteristics are discussed. It is shown that multistage drawing succeeds in achieving a higher tensile strength and elastic modulus (1.2 and 35 GPa, respectively) than the orientational crystallization, which gives 0.8 and 15 GPa. The strengthening by drawing is accompanied by microcrack formation. In contrast, no discontinuities are observed in orientationally crystallized samples up to their ultimate extension.FLWNAinfo:eu-repo/semantics/publishe

Evolution of the Surface Structure and Functional Properties of the Electroconducting Polymer Coatings onto Porous Films

Composite systems containing electroconducting polymer coatings (polyaniline and polypyrrole) applied to porous films of semicrystalline polymers (polyethylene, polypropylene, and polyvinylidene fluoride) have been prepared. Porous supports were obtained in the process based on polymer melt extrusion with subsequent annealing, uniaxial extensions, and thermal stabilization. Conducting coatings were formed by the oxidative polymerization of the monomers directly onto the porous supports. The structure (overall porosity, permeability, pore sizes, factor of orientation) and morphology (specific surface and character of the film surface) of the supports were characterized by sorptometry, filtration porosimetry, atomic force microscopy (AFM), and X-ray scattering techniques. It was observed that the porous supports have a strongly developed relief surface which is formed in the pore formation process. It was proven by scanning electron microscopy (SEM) that the porous supports have an oriented structure, and the surface of the composites is defined by the morphology inherent in the conducting component. It was shown that these composites (porous support/conducting coating) demonstrate electric conductivity both along the surface and between surfaces. It was demonstrated that the deposition of conducting coatings leads to an increase in the water wettability of the composites compared with pronounced hydrophobic supports. The composites are characterized by good adhesion between components due to a relief film surface as well as high mechanical strength and elasticity provided by the oriented character of the supports