Search

In this work, film materials based on binary compositions of poly-(3-hydroxybutyrate) (PHB) and chitosan with different ratios of polymer components in the range from 0/100 to 100/0 wt. % were studied. Using a combination of thermal (DSC) and relaxation (EPR) measurements, the influence of the encapsulation temperature of the drug substance (DS) of dipyridamole (DPD) and moderately hot water (at 70 °C) on the characteristics of the PHB crystal structure and the diffusion rotational mobility of the stable TEMPO radical in the amorphous regions of the PHB/chitosan compositions is shown. The low-temperature extended maximum on the DSC endotherms made it possible to obtain additional information about the state of the chitosan hydrogen bond network. This allowed us to determine the enthalpies of thermal destruction of these bonds. In addition, it is shown that when PHB and chitosan are mixed, significant changes are observed in the degree of crystallinity of PHB, degree of destruction of hydrogen bonds in chitosan, segmental mobility, sorption capacity of the radical, and the activation energy of rotational diffusion in the amorphous regions of the PHB/chitosan composition. The characteristic point of polymer compositions was found to correspond to the ratio of the components of the mixture 50/50%, for which the inversion transition of PHB from dispersed material to dispersion medium is assumed. Encapsulation of DPD in the composition leads to higher crystallinity and to a decrease in the enthalpy of hydrogen bond breaking, and it also slows down segmental mobility. Exposure to an aqueous medium at 70 °C is also accompanied by sharp changes in the concentration of hydrogen bonds in chitosan, the degree of PHB crystallinity, and molecular dynamics. The conducted research made it possible for the first time to conduct a comprehensive analysis of the mechanism of action of a number of aggressive external factors (such as temperature, water, and the introduced additive in the form of a drug) on the structural and dynamic characteristics of the PHB/chitosan film material at the molecular level. These film materials have the potential to serve as a therapeutic system for controlled drug delivery.

The article is focused on the study of segmental dynamics in electrospun PHB fibers and the same fibers subjected to cold rolling based on the analysis of a spin probe characteristics obtained by ESR technique. It was found that the presence of two TEMPO probe populations with different correlation times indicates the heterogeneous structure of intercrystalline areas in the fibrous materials and in cold-rolled fibrous materials. The ESR data shows a model of the amorphous state in semicrystalline polymers. The study uses the ESR technique data for the analysis of water impacts on probe mobility. It is shown that the electrospun fibers, and especially the fibers after cold rolling, lead to denser field formation in the intercrystalline area of PHB, thus favoring fiber stabilization against the exterior water.

Ultrathin fibers based on poly-3-hydroxybutyrate were obtained by electrospinning with weak concentrations of the iron (III) – tetraphenylporphyrin complex. By the SEM, DSC and EPR methods, it is shown that the addition of the complex to the polymer solution leads to the disappearance of fiber defects in the form of thickenings; moreover, this adding leads to a sharp increase in crystallinity and a slowdown in molecular mobility in the amorphous regions of ultrathin fibers. The obtained fibrous materials have bactericidal properties, and they must find direct application in the creation of therapeutic systems of antibacterial and antitumor action.

In this paper, we study the effect of rolling on the structure of fibrous materials based on poly(3-hydroxybutyrate) (PHB) and obtained by electrospinning. We have used electron paramagnetic resonance to demonstrate the effect of water and an oxidant (ozone) on the amorphous phase of the PHB matrix, formed by ultrathin fibers. We have established that additional orientation of PHB spherulites in a mechanical field leads to stabilization of the amorphous regions, which are more resistant to exposure to an aggressive ozone atmosphere. Studying the DSC curves for melting of the fibrous materials has shown that mechanical rolling leads to a bimodal distribution of the crystalline phase into more perfect and less perfect crystalline regions. The series of studies of ultrathin fibers proposed made it possible to analyze the changes in the segmental mobility of the polymer molecules in the early stages of their interaction with aqueous and oxidizing aggressive environments.

In the treatment of many infectious diseases and cancer, transdermal systems based on solid polymer matrices or gels containing functional substances with antiseptic (antibacterial) properties are often used. One of the most promising types of matrices with antiseptic properties are the ones of nano- and microfiber-bonded cloth obtained by electrospinning based on biopolymer poly(3-hydroxybutyrate). The present work investigates the effects of iron (III) complex with tetraphenylporphyrin and the influence on the geometry, crystalline order and molecular dynamics in the intercrystalline (amorphous phase) of ultrathin PHB fibers.

Adhesion and mechanical properties of vinyl aromatic thermoplastic elastomers on the Russian market were studied. Significant differences between the materials were shown that are due to differences in the chemical natures and structural parameters of block copolymers.

The fibrous materials (the mats) based on poly-3-hydroxybutyrate (PHB) containing the drug, dipiridomole (DPD) were produced by electrospinning (ES). Thermophysical and dynamical properties of the single filaments and the mats were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and probe electron paramagnetic resonance spectroscopy (EPR). The effect of annealing temperature on the structure and crystallinity of the fibers was examined. It was shown that the loading of DPD influences on both the melting enthalpy and the morphology of the fibers. Besides the analysis of EPR spectra revealed that there are two populations of spin-probes distributed in the rigid and nonrigid amorphous regions of the PHB fibers respectively. For all fibrous materials with different content of DPD (0–5%) the correlation between thermophysical (DSC) and dynamic data (EPR) was observed.

The thermooxidative behavior of isotactic PP in the presence of ethylene-propylene oil was studied. The rate curves of oxygen uptake by oil-extended PP have the S-shaped pattern characteristic of chain oxidation with the degenerate branching of kinetic chains. The introduction of oil into the polymer lowers its oxidation rate. It was found that the mechanism of oxidation of oil-extended PP depends on the oil content and the sample cooling mode. By means of X-ray diffraction, differential scanning calorimetry, and IR spectroscopy, the structural and thermophysical parameters of oil-extended PP were determined. It was found that the cooling conditions and the oil content of the specimens have an effect on the structure of amorphous and crystalline regions, thereby affecting the PP thermooxidation kinetics. The influence of the phase state of the system on the reactivity of oil-extended PP is considered.

Optimal photoperiod and temperature conditions for rearing of the mosquito Culex pipiens pipiens f. molestus without blood feeding (through autogenous eggs) were experimentally substantiated. This method may be used in order to obtain relatively small quantities of mosquitoes or for preservation of a laboratory colony. Optimal conditions of rearing are the short-day photoperiod (12 h of light per day) at 20 degrees C, when 87 % of the females produce autogenous eggs rafts consisting of 52 eggs on the average. It should be emphasized that larval food must be adequate and abundant, because the quality and quantity of it has a pronounced effect on the autogeny rate.

The distribution of the urban mosquitoes, Culex pipiens pipiens f. molestus in Petrozavodsk city was studied for the first time. Immature mosquito stages were found in 21 of 68 basements flooded with polluted waters, the occurrence of the mosquitoes varied in different districts of the sity. The mean siphonal index of the mosquito larvae from 6 underground populations varied from 3.8 up to 4.2, i. e. within the range typical for C. p. p. f. molestus.

Holography is mainly applied for recording and reconstructing the wave field giving information about the object under study that is mostly a three''-dimensional one. In the present paper the holograms are supposed to be used for testing colorimeters employed in various branches of the national economyl. In this case a reference standard is a reflection hologram of diffuse surface. The spectral distribution J1(X) of its reconstructed light flux is certified by a high precision spectrophotometer and converted into colour coordinates. Carried out in the paper is the calculation of the hologram reconst ruction conditions and given are the results of the experimental re cording of holograms and reconstruction thereof. 1. CALCULATION OF HOLOGRAM RECONSTRUCTION CONDITIONS When working out the practical schemes of recording and reconst ructing holographic colour specimens it is essential to know how the wavelength of the reconstructed radiation A1 is changed with the change of the angle of incidence ac 0f the reconstructing beam of white light. To calculate X let us use the Bragg equation2: XI n2d Sin c (1) where d period of interference pattern c - the angle between direction of reconstructing beam in medium and plane of interference pattern n - refractive index of medium. Using the beam plotting when recording and reconstruction of the hologram are carried out (Fig. l) we shall obtain the expression for A1 2nA A - R I