A. N. Zelenetskii

Effect of direct-current discharge treatment on the surface properties of chitosan-poly(L,L-lactide)-gelatin composite films

The surface of films made from a chitosan-poly(L,L-lactide)-gelatin mixture stabilized with a grafted-copolymer fraction has been modified by dc discharge treatment, as well as that of films made of the individual components. The surface properties of the films (wettability, surface energy), the chemical structure of surface layers, and their morphology have been examined by goniometric measurement of contact angles, X-ray photoelectron spectroscopy, and scanning electron microscopy.

Solid-state synthesis of amphiphilic chitosan-polyethylene systems by the maleinization of both components

N-acylated chitosan modified by maleic anhydride was prepared by the method of the solid-state synthesis (Bridgman anvils, semipilot extruder). In contrast to the synthesis under homogeneous conditions, solid-state acylation is accompanied by the reaction of imidization of the formed amic acid as well as by reaction through double bonds, thus leading to the formation of derivatives of succinic anhydride. By simultaneous or subsequent interaction of chitosan modified with maleic anhydride with a PE matrix, either modified or not modified with maleic anhydride, new chitosan-polyethylene composite materials are prepared, and these composites are characterized by the combined valuable medicinal and biochemical properties of chitosan and high mechanical characteristics of the polyolefin component. The above composites are of obvious interest as amphiphilic sorbents, which are highly resistant to the action of aggressive media, as well as antimicrobial and biodegradable PE-based materials.

Effect of borax additives on the rheological properties of sodium hyaluronate aqueous solutions

The rheological properties of sodium hyaluronate aqueous solutions are studied, and the effect of borax additives on them is investigated. It is shown that, at low concentrations, sodium hyaluronate behaves as a typical linear polyelectrolyte in the limit of a high concentration of the salt in both a 0.1 M NaCl aqueous solution and a salt-free solvent. The addition of 1 mole of borax per base-mole of the polymer to the solution of sodium hyaluronate significantly decreases the specific viscosity of the solution if no salt is added and has practically no effect on the viscosity of the solution in 0.1 M NaCl. The viscosity of a semidilute solution of sodium hyaluronate without the added salt decreases as the shear rate is increased in the range 1.5–656 s−1. With an increase in temperature, viscosity decreases and its dependence on shear rate becomes less pronounced. The same effect is exerted by small amounts of borax. The properties of salt-free solutions are explained by the presence of admixtures of low-molecular-mass ions in them that screen the Coulomb repulsion of charges linked to sodium hyaluronate chains, and the effect of borax may be rationalized by the screening effect of ions resulting from the hydrolysis of borax.

The study of the interaction between chitosan and 2,2-bis(hydroxymethyl)propionic acid during solid-phase synthesis

New polymer salts and N-acetylated chitosan derivatives are prepared in an extruder by the method of solid-phase synthesis via the interaction of chitosan and 2,2-bis(hydroxymethyl)propionic acid. The effect of the initial component ratio and temperature on the yield and structure of the target products is studied. Joint deformation of solid components at room temperature is found to cause the quantitative formation of salt bonds between carboxylic groups of the acid and amino groups of chitosan. At elevated temperatures of synthesis, the corresponding acetylated derivatives with a degree of substitution of amino groups varying from 0.16 to 0.43 are prepared. The relaxation and phase transitions in the polymer salts and acetylated chitosan derivatives and their sorptional activity are studied. The films prepared from aqueous solutions of the new salt modification of chitosan are characterized by a homogeneous structure and improved mechanical characteristics relative to those of the films based on chitosan acetates. An additional thermal treatment of the products of the solid-phase synthesis leads to the formation of crosslinked and water-swollen materials that can be used for the development of novel polymeric chitosan-based membranes and sorbents.

Modification of the chitosan structure and properties using high-energy chemistry methods

Literature on the modification of the natural polymer chitosan using high-energy chemistry methods (treatment by a low-temperature plasma, with an electron beam, energetic ions, or γ-iradiation) has been surveyed. The basic chitosan treatment procedures and facilities used in the processes have been described. The instrumental techniques used to study changes in the chemical structure and properties of modified chitosan have been considered. Data showing the possibility of using modified chitosan in medicine and biotechnology have been presented.

Amphiphilic systems based on polysaccharides produced by solid-phase synthesis − A review

The results of research on polymer blends based on polysaccharides (chitin, chitosan, cellulose, starch, etc.) and variously hydrophilic synthetic polymers produced by reaction mixing in solid state under pressure and shear stresses are summarized. The mechanisms of the processes occurring under solidphase synthesis conditions, the properties of the multicomponent systems formed, and the feasibility of their application for creating new biocompatible and biodegradable materials are discussed.

A Novel Approach to Design Chitosan-Polyester Materials for Biomedical Applications

A novel approach to design chitosan-polyester materials is reported. The method is based on mechanical activation and effective intermixing of the substrates under high pressure and shear deformation in the course of solid-state reactive blending. The marked departure of this approach from previous practice resides on exploitation of a variety of chemical transformations of the solid polymers that become feasible under conditions of plastic flow. Low temperatures (above Tg but below the melting points of the crystalline polymers) are maintained throughout the process, minimizing mechanical and oxidative degradation of the polymers. Morphology as well as structural, mechanical, and relaxation properties of those prepared blends of chitosan with semicrystalline poly(L,L-lactide) and amorphous poly(D,L-lactide-co-glycolide) has been studied. Grafting of polyester moieties onto chitosan chains was found to occur under employed pressures and shear stresses. The prepared polymer blends have demonstrated an amphiphilic behavior with a propensity to disperse in organic solvents that widens possibilities to transform them into promising materials for various biomedical applications.

Nanocrystalline Cellulose from Flax Stalks: Preparation, Structure, and Use

Preparation of nanocrystalline cellulose by acid hydrolysis of flax cellulose is described. According to atomic-force microscopy, the obtained nanocrystals were needle-like with average diameter 85 ± 39 nm and length 158 ± 89 nm. The potential of using nanocrystalline flax cellulose as an adhesive for heat-protective porous ceramics and an anisotropic reinforcing filler of polymer films was investigated.

Thermostimulated processes in starch-bis(hydroxymethyl)propionic acid mixtures subjected to high-pressure plastic deformation

DSC and thermogravimetry are employed to study starch, bis(hydroxymethyl)propionic acid, and their mixtures of different compositions subjected to plastic deformation under pressures of 1 and 3 GPa. An endothermic peak with an enthalpy of 300 J/g observed in the thermogram of starch is most likely related to the breakage of hydrogen bonds. Treatment under pressure greatly reduces the enthalpy of this peak. For initial mixtures, the enthalpies of the endothermic peak of starch and the endothermic peak of melting of the acid are lower than those for individual components because of chemical interaction occurring between the mixture components during heating. The high-pressure treatment makes the decrease in the enthalpy of endothermic processes much more pronounced for both components.

Two-Photon-Induced Microstereolithography of Chitosan-g-Oligolactides as a Function of Their Stereochemical Composition

Chitosan-g-oligolactide copolymers with relatively long oligolactide grafted chains of various stereochemical compositions have been synthetized via a solvent-free mechanochemical technique and tailored to fabricate three-dimensional hydrogels using two-photon induced microstereolithography. An effect of the characteristics of chitosan and oligolactide used for the synthesis on the grafting yield and copolymer’s behavior were evaluated using fractional analysis, FTIR-spectroscopy, dynamic light scattering, and UV-spectrophotometry. The lowest copolymer yield was found for the system based on chitosan with higher molecular weight, while the samples consisting of low-molecular weight chitosan showed higher grafting degrees, which were comparable in both the cases of l,l- or l,d-oligolactide grafting. The copolymer processability in the course of two-photon stereolithography was evaluated as a function of the copolymer’s characteristics and stereolithography conditions. The structure and mechanical properties of the model film samples and fabricated 3D hydrogels were studied using optical and scanning electron microscopy, as well as by using tensile and nanoindenter devices. The application of copolymer with oligo(l,d-lactide) side chains led to higher processability during two-photon stereolithography in terms of the response to the laser beam, reproduction of the digital model, and the mechanical properties of the fabricated hydrogels.