A. A. Berlin

Debonding microprocesses and interfacial strength in particle-filled polymer materials

Griffith energy theory was developed for analysis of crack propagation along an interface in polymers filled with rigid spherical inclusions. A polydisperse structural model was used for stress-strain distribution analysis of composite materials. Experiments were performed on glass-bead filled polyethylene and polypropylene and epoxy resin. The dependence of debonding stresses and angles on contraction stress, friction, particle diameter and material characteristics were analysed.

Phenomenological description of the spontaneous formation of macroscopic strings in low-concentration chiral solutions and the formation of anisometric gels

36 Gel formation has recently been described in chiral solutions of low concentrations (10–3 to 10–2 M) [1], which are two orders of magnitude lower than the per colation threshold for the formation of an isotropic gel [2]. The forming gel has a well discernible microstruc ture [1]. Examination of the xerogel produced after solvent evaporation from the samples detected aniso metric (with a length to diameter ratio of 103–105) structural elements with observable rigidity—strings [1, 3, 4]. In this work, we identified the phenomena that lead to the solidification of low concentration chiral solu tions and studied the solidified phase by the example of solutions of trifluoroacetylated amino alcohols (TFAAA) (table). TFAAA molecules are chiral (except compound 4 in the table) and approximately isometric, which allows one to exclude the effect of nonchiral steric factors on solidification. The molecu lar design of TFAAA ensures the manifestation of the full range of weak intermolecular interactions in the formation of supramolecular structures. The solutions we used were cyclohexane, chloroform, carbon tetra chloride, benzene, ethanol, methanol, and acetone. The solution microstructure was investigated by optical microscopy. Solvent evaporation was pre vented because the samples of the studied solutions were placed in closed vessels. At a concentration on the order of 10–3 M and higher and a temperature of 300–340 K, a condensed phase separates out from homochiral TFAAA solu tions. On cooling a solution within a capillary 300 μm i.d., the phase separates out as an individual discrete anisometric structural element or elements—strings (Fig. 1). The string diameter (1–3 μm) is constant, and the string length reaches several millimeters. The strings form approximately along the capillary axis, definitely being repelled from the capillary walls and showing no signs of interacting with each other. Thus, the string formation in these experiments is a separate physical phenomenon unrelated to gel formation.

Structure and prolonged transport in a biodegradable poly(R-3-hydroxybutyrate)-drug system

In order to create new biodegradable systems for the targeted transport of drugs, poly(3-hydroxy-butyrate) films containing the antibiotic rifampicin in an amount of 5–15 wt % as a model drug are prepared. Film surfaces are studied via scanning electron microscopy, and various structural elements (globules and fibrils) are found. Polymer samples isolated from melt or solution feature different degrees of porosity. It is shown that the kinetic profiles of rifampicin release are of an abnormal character. An analysis of the profiles shows that the release of rifampicin is controlled by the superposition of two processes: its desorption via the diffusion mechanism (the nonlinear segment) and hydrolytic degradation of poly(3-hydroxybutyrate) (the extended linear segment), which becomes well defined after completion of the diffusion stage. The diffusionkinetic model of the process is developed.

A study of the chemical structure of the surface of carbon fibers before and after oxidation

Treatment of carbon fibers of different brands was carried out using gas phase thermal oxidation. It was found that microstructures of amorphous carbon, edges of graphite-like packs, and graphene ribbons in fibrils with uncompensated valence changed at oxidation. Paramagnetic absorption of carbon fibers was investigated. It was established experimentally that the paramagnetic susceptibility centers of carbon fibers and centers, where adsorption of methanol and krypton molecules takes place, are identical. It was shown that the highest concentration of paramagnetic centers and the highest strength of adhesive interaction were obtained for carbon-fiber-reinforced plastic based on carbon fiber of Elur-0.1P brand.

Effect of external influences on the structural and dynamic parameters of polyhydroxybutyrate-hydroxyvalerate-based biocomposites

The EPR probe, DSC, and WARDX methods are applied to study the molecular dynamics and structure of 3-hydroxybutyrate-3-hydroxyvalerate copolymer (PHBHV, 5 mol %) and its mixtures with segmented polyester urethane (SPEU) upon ozone oxidation and hydrothermal treatment. It is shown that time-limited (3 and 5 h) treatment of the mixed compositions with water at 40°C has no noticeable effect on the dynamics of rotation of the probe (EPR) and the crystallinity of PHBHV (DSC). However, hydrothermal treatment at 70°C causes an increase in the molecular mobility of the probe in the system, accompanied, according to XRD and DSC analyses, by increases in the degree of crystallinity and density of PHBHV crystallites. The temperature of fusion of mixed compositions also increases. During ozonation, the mobility of the probe slows gradually in PHBHV all the time, whereas in mixed compositions, a slowdown is observed only up to 3 h of oxidation time, after which, up to 5 h of ozonation, the mobility increases, along with decreases in the fraction of the amorphous phase and in the density of the crystallites.

Probe mobility dynamics, crystal structure, and isotope exchange in PHBV and SPEU blend compositions

176 Biodegradable compositions based on natural polymers in combination with synthetic polymers offer an alternative to individual polymers. Blending is expectable to endow the composition with some new physicochemical characteristics that are not intrinsic to its individual components. Innovation technologies employ biodegradable systems for the targeted trans port of drugs and for the manufacture of environmentally friendly construction materials and packaging [1, 2]. Due to the unique combination of thromboresistance and mechanical characteristics, segmented polyether urethanes (SPEUs) are widely used in diverse fields of engineering and biomedicine as construction and functional materials. However, dimethyl isocyanate– based SPEUs are well known to have low biodegrada tion rates. This is a positive factor where long opera tion times are required, but may be considered as a limitation for short times of use. The lifetime of a sys tem can be tailored by blending SPEUs with other biopolymers, such as polyhydroxyalkanoates [3]. Poly(3 hydroxybutyrate) (PHB), a representative poly hydroxyalkanoate, combines useful properties with some undesired properties, namely, high costs and fra gility. These limitations are eliminated by PHB copol ymers with 3 hydroxyvalerate (PHBV) and composi tions with other biomedical polymers, in particular, with chitosan [4]. Varying the component ratio of the PHBV–SPEU composition and thereby influencing the morphology and crystallinity, one can manufac ture composition materials with diversified physico chemical characteristics, such as permeability, water solubility, destruction mechanism and destruction rates, and others. An efficient way to evaluate the states of amor phous and crystalline phases in polymers and polymer blends is a combination of dynamic and structural techniques. In this study, the dynamic techniques used are electron probe microanalysis, ESR, and deuterium isotope exchange. The structural techniques used are wide angle X ray diffraction and differential scanning calorimetry (DSC). Such a combination of structural and dynamic characteristics allows a more complete ascertainment of the structural evolution of PHBV– SPEU blends in an aqueous medium, preceding the hydrolytic decomposition of the polymer system, in the range of small times (hours). The subject matter of this study was blend compo sitions based on a PHBV biodegradable natural copoly mer (from Tianan) and SPEU (from BASF Elastog ran). The characteristics of the individual components were as follows: for SPEU: Mw = 2.29 × 10 5, Mn = 5.3 × 104, and ρ = 0.97 g/cm3; and for PHBV: Mw = 2.4 × 10 5, Mn = 1.5 × 10 5, and ρ = 1.25 g/cm3. The component ratio in PHBV–SPEU blends was varied in the follow ing sequence (wt/wt): 60 : 40, 50 : 50, and 40 : 60. Polymer films were prepared by evaporating a solvent (chloroform or tetrahydrofuran) from polymer solu tions on glass surfaces. Molecular mobility was studied by a spin probe method with determination of the correlation time τ, which characterizes the rotation mobility of the TEMPO probe, using a conventional ESR procedure [5]. DSC studies were carried out on a Netzsch DSC 204 F1 analyzer in an inert (argon) atmosphere with a heating rate of 10 K/min. X ray dif fraction was measured from film samples in transmis sion geometry on a Bruker Advance D8 diffractometer (CuK α radiation). The IR spectra of deuterated films were recorded on a Bruker IFS 48 FTIR spectropho tometer with a resolution of 2 cm–1 using 256 scans for each spectrum. X ray diffraction measurements showed high crys tallinities of PHBV and PHB samples [4]. The X ray diffraction patterns of PHBV films show at least five reflections corresponding to an orthorghombic lattice PHYSICAL CHEMISTRY

Plug-Flow Tubular Turbulent Reactors: A New Type of Industrial Apparatus

Chemical apparatuses of a new type, specifically, quasi-isothermal plug-flow divergent–convergent tubular turbulent continuous reactors, are considered. These apparatuses combine the merits of plug-flow tubular reactors and stirred continuous reactors and have some technical and technological advantages.

Structure and properties of ultrathin poly-(3-hydroxybutirate) fibers modified by silicon and titanium dioxide particles

The influence of small concentrations of nanoscale silicon and titanium dioxide particles on the structure, physicomechanical and sorption properties, thermal destruction resistance, and thermal and photo oxidant destruction of unwoven ultrathin fibrous materials that are prepared via electrostatic solution spinning is studied. It is established that nanoscale particles favor the formation of thinner fibers with improved physical and mechanical parameters; good resistance to thermal, thermo- and photo oxidant destruction; and positive dynamics of mesenchymal stem cells.

Advances and Problems of Frontal Polymerization Processes

The main stages of the development of frontal polymerization are presented. The processes taking place at cryogenic temperatures, under high (up to 5 kbar) pressures and usual conditions, when the polymerization is performed in glass ampoules without excessive pressure, are discussed. Depending on the Semenov parameter, the conditions of polymerization in low-temperature quasi-isothermal and high-temperature adiabatic or frontal thermal modes are considered. Theoretical and experimental data for the dependence of the front velocity on the various parameters. The influence of the nature of initiator, monomer, and dispersed inorganic on the reaction order with respect to the initiator is analyzed. Monomers polymerizing in the reaction front propagation are classified regarding their polymerization rates and boiling temperatures. The articles of various authors devoted to the synthesis of polymer materials and polymer-based composites difficult to obtain under conventional conditions are considered. The reactors of frontal polymerization in turbulent and laminar flows, widely applied in practice, are studied. Certain conclusions are made on the further development of frontal polymerization processes on the basis of data available in the literature.

Simulation of melting in crystalline polyethylene

We carry out a molecular dynamics simulation of the first stages of constrained melting in crystalline polyethylene (PE). When heated, the crystal undergoes two structural phase transitions: from the orthorhombic (O) phase to the monoclinic (M) phase, and then to the columnar (C), quasi-hexagonal, phase. The M phase represents the tendency to the parallel packing of planes of PE zigzags, and the C phase proves to be some kind of oriented melt. We follow both the transitions O→M and M→C in real time and establish that, at their beginning, the crystal tries (and fails) to pass into the partially ordered phases similar to the RI and RII phases of linear alkanes, correspondingly. We discuss the molecular mechanisms and driving forces of the observed transitions, as well as the reasons why the M and C phases in PE crystals substitute for the rotator phases in linear alkanes.