Microorganisms of the genus Bacillus were shown to have different effects on the degradation of polylactide packaging material. The degradation experiment was carried out on an agar medium at a temperature of 55°C and pH 5.9 for 14 days. This is the first report on the abiotic hydrolysis significantly slowing down during incubation with B. licheniformis S8 and occurring in parallel with the main process, enzymatic hydrolysis. The latter involved sequential cleavage of monomer units from the end of the macromolecule and the formation of low molecular weight products used by microorganisms as a substrate; it contributed to a decrease in the mass of polylactide by 5.1

A nanocomposite based on high-density polyethylene with barium titanate (content of 13 – 15 wt. %) was obtained as a result of low-temperature synthesis of the inorganic component directly in the mesopores of an oriented polymer matrix using the sol-gel method followed by hydrothermal treatment in an alkaline medium. Crystallization of barium titanate in nanopores is detected by X-ray phase analysis and electron microscopy to occur mainly in a cubic crystalline modification with an average crystallite size of 16 nm and to form chain structures. A comparative assessment of the dielectric properties of a polymer nanocomposite and powder barium titanate synthesized under similar conditions is carried out.

Effect of the structural mechanical modification via the crazing mechanism and composition of films based on HDPE nanocomposites and highly dispersed silica particles on the thermo-oxidative degradation and pyrolysis is studied. The incorporation of highly dispersed silica particles into the polymer matrix causes a reduction in the onset temperature of the intense weight loss of the composites by about 30°С and an increase in the temperature interval by 100°С under conditions of thermo-oxidative degradation. It is shown that in pyrolytic decomposition the HDPE‒SiO2 composite also starts to lose weight at lower temperatures (smaller by 50°С). Using various kinetic approaches to process the TGA curves the activation energy for each stage of thermal oxidation and pyrolysis is determined for structurally different HDPE-based samples. In the case of thermo-oxidative degradation, dependence of the activation energy on conversion is shown to be complex, thereby reflecting the multistage nature of the process. In pyrolysis, the activation energy is almost constant at all stages of the process. For various models of the processes, the activation energy is calculated by the Coats–Redfern method and the most probable mechanisms of thermal degradation and pyrolysis of the samples are proposed.

Polylactide-based materials are often considered an alternative to materials produced from traditionally hardly degradable polymers. Porous polylactide membranes, matrices, and scaffolds are especially attractive for use in biomedicine. The review concerns the physicochemical basis and structural and morphological opportunities of various methods for the manufacture of porous polylactide, such as sintering, 3D printing, electrospinning, foaming, etching, and the processes of phase separation and orientational drawing. Special attention is focused on the effect of porous structure parameters on the rate of hydrolytic degradation of the polymer and the prospects for the development of application areas of similar porous materials.

An alternative method for production of hybrid organic–inorganic nanocomposites based on porous polyolefin films (isotactic polypropylene, high density polyethylene), deformed via crazing mechanism in physically active media, and calcium phosphates is proposed. Film composite materials of different structure and containing 10–25 wt % of filler are obtained. Particles of calcium hydroxyapatite with a diameter of 15–50 nm are formed in these films at once in the pores of the polymer matrices with the development of a layer, the morphology of which is determined by the structure of the original porous films, and its parameters can be controlled by the reaction conditions. It is found that the composites obtained are characterized by anisotropy of mechanical properties, and the introduction of the calcium phosphate particles results in some increase in the mechanical characteristics of the polymer matrices. High-temperature heating (up to 700°C) of nanocomposites leads to burning out of the polymer matrix and formation of porous calcium hydroxyapatite residues consisting of nanoparticles with different morphology depending on the initial porous structure of polymer (from needle-shaped crystals with a length of 100–150 nm and about 10 nm in diameter to spheres with a diameter of 50–90 nm). The results obtained are relevant for the directional regulation of the structure and properties of bioactive substances and creation of modern materials for biomedical use.

Systematic investigations of uniaxial deformation of an amorphous isotropic polylactide film in water–ethanol solutions of different composition are carried out and optimal conditions for polymer deformation by the crazing mechanism are determined. In the whole range of the solution compositions, the polylactide deformation is accompanied by the formation of a highly dispersed fibrillar-porous structure according to the mechanism of classical crazing. When the ethanol content is ~35 wt %, the film deformability increases sharply, and it reaches 400–500% in solutions with the ethanol content of more than 45 wt %. The fine structure of the polylactide crazes during deformation in a 50% aqueous ethanol solution is studied in situ by X-ray scattering at small angles. The intensity distribution curves for polylactide samples, regardless of the degree of deformation, are characterized by the presence of an interference maximum, which indicates the regular arrangement of the individual fibrils in crazes relative to each other. The interfibrillar distance is 40 nm at the degree of deformation up to 200%. Composite materials containing nanoparticles (average crystallite size is ~30 nm) of various biologically active calcium phosphates are obtained on the basis of porous polylactide matrices (with a volumetric porosity of ~45 vol %) using the method of countercurrent diffusion between aqueous solutions of calcium nitrate and ammonium hydrogen phosphate. The filler content has reached 30 wt %. Such organomineral materials are considered promising in the field of biomedicine.

The influence of various liquid media (aliphatic alcohols, water-alcohol solutions, saturated hydrocarbons, and organosilicon liquids) on the development of uniaxial deformation and nucleation of crazes in amorphous polylactide (PLA) films has been studied. It has been found that in the presence of the liquids the tensile stress during the polymer deformation decreases by 3-4 times. According to the Griffith's theory, linear dependences (with an accuracy of R-2 = 0.96-0.97) have been revealed between the yield point or the flow stress of PLA and the square root of product of the elasticity modulus of the polymer in a liquid and the interfacial surface energy at the polymer-liquid medium interface calculated using the Owens-Wendt equation. The data obtained may be used to predict the critical mechanical stress at which crazes will be initiated in PLA. (C) 2018 Elsevier Ltd. All rights reserved.

With usage of crazing and counterdiffusion ZnO/HDPE (High Density PolyEthylene), polymer nanocomposites were obtained and their microstructure and optical properties were studied. Size of the Zinc oxide nanoparticles in ZnO/HDPE composites is 18±2 and 24±2nm when synthesized from alcohol and aqueous solutions respectively. In the case of synthesis from alcohol solutions, more even distribution of inorganic phase in a polymer matrix was observed. The highest content of inorganic component in composites obtained amounted up to 30% by mass. Polymer nanocomposites obtained were used as a substrates for growth of ZnO nanorods array. When synthesizing on a polymer nanocomposites obtained from a aqueous solution, length of the nanorods, according to statistical analysis of scanning electron microscopy (SEM) microphotographs, was about 2.5μm, while using alcohol solution nanorods of 1.1μm in length were produced at the same conditions. According to SEM microphotographs, morphology of nanorods varies depending on the method of synthesis of ZnO seeds in polymer matrix.

The effect of a finely divided structure created via the mechanism of delocalized crazing on the processes of thermo-oxidative degradation of isotactic polypropylene has been studied. It has been shown that the thermal stability of porous films is reduced at relatively low temperatures (up to 155°C) and they become brittle. In contrast, their degradation rate at temperatures above 400°C is two times below that for the original, nonporous films because of the formation of crosslinked network structures and carbonization. The formation of titania and silica nanoparticles via hydrolytic decomposition of the respective alkoxides directly in the pore space of the polypropylene matrix substantially alters its thermal stability, depending on the precursor concentration, the extent of hydrolysis, and the composite structure. The greatest increases in the mass-loss-onset temperature and the temperature of the maximum mass-loss rate (by 80–100°C) have been observed for the composites with 40 wt % titanium dioxide. It has been assumed that the enhancement of thermal stability is due to the significant concentration of the products of incomplete hydrolysis of titanium alkoxy derivatives. The silica particles, in contrast, exert a signification influence on the thermo-oxidative-degradation processes in polypropylene at their low concentration (up to 5 wt %), a result that is associated with the structural features of such composites.

Рассмотрено влияние высокодисперсной структуры, созданной по механизму делокализованного крейзинга, на процессы термоокислительной деструкции изотактического полипропилена. Показано, что до относительно низких значений температуры (155°C) термостабильность пористых пленок понижается, они становятся хрупкими. При температуре выше 400°C, напротив, скорость их деструкции в 2 раза ниже, чем для исходных непористых пленок, благодаря формированию пространственно сшитых структур и коксованию. Формирование наночастиц диоксидов титана и кремния путем гидролитического разложения их алкоголятов непосредственно в объеме пор матрицы полипропилена существенно изменяют ее термостабильность в зависимости от концентрации прекурсора, глубины процессов гидролиза и структуры композитов. Наибольшее увеличение температуры начала и максимальной скорости потери массы (на 80–100°C) наблюдалось для композитов с 40 мас. % диоксида титана. Выдвинуто предположение, что повышение термостабильности происходит, благодаря значительному содержанию продуктов неполного гидролиза алкоксипроизводных титана. Ощутимое влияние частиц диоксида кремния на процессы термоокислительной деструкции полипропилена, напротив, наблюдается при их низком содержании (до 5 мас. %), что связано со структурными особенностями таких композитов.

Magnetic and structural properties of magnetite nanoparticles stabilized in polyvinyl-alcohol thin films are investigated by using X-ray diffraction (XRD), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) and static magnetometry techniques. The nanoparticles have well-defined crystallinity, and are superparamagnetic at room temperature. Their size distribution is characterized by the distinct log-normal law (with average diameters near 5-7 nm) and slight maximum near 7080 nm. The EPR spectra and static magnetization data demonstrated pronounced anomalies in the interval between 130 K (corresponding to Verwey transition) and 200 K. The experimental data obtained can be understood on the basis of the half-metallic electronic structure, complex temperature behavior of the magnetic anisotropy, along with effects of "weak magnetic-electron'' sublattice of the magnetite. (c) 2013 Elsevier B.V. All rights reserved.

A method is developed for crazing-based production of mechanically strong hybrid polypropylene film composites containing amorphous titanium dioxide nanophase (up to ∼30 wt %). As a whole, the morphology of the composite represents an interpenetrating network in which the inorganic component (TiO 2 ) is distributed in the nanoporous structure of a polypropylene matrix. The structure and composition of amorphous titanium dioxide present an ensemble of TiO 2 nanoparticles with a size of ∼1 nm (20 wt %) included in a loose network of titanium oxopolymers (80 wt %) containing ∼30 wt % side OC 3 H 7 and OH groups bonded to titanium atoms.