The effectiveness of single-layer actuators based on polymer matrix with branched networks of stimulus-sensitive component is proposed and approved. The study is performed for humidity-driven actuators with polar liquid adsorbing filler. The actuators are produced using a delocalized crazing mechanism to create an interpenetrating pore structure, in which silica gel is formed from ethyl silicate during hydrolysis. The actuator bends towards a lower humidity side and demonstrates a strong response to humidity changes within a few seconds. The enhanced performance of the actuator is realized by adjusting the pore structure and the filler content. The dependencies of the curvature of the bent film and the response time to a humidity change on filler content, show a non-monotonic behavior with a maximum and minimum, respectively. With a solvent polarity increase, the curvature firstly increases and then reaches a plateau. The theory is developed to describe the actuator response to variations in humidity, filler content, crazing strain, temperature. The obtained actuators maintain the initial bending properties for more than 100 cycles and reach the curvature of 2.9 cm-1 at the crazing strain of 200 % and the SiO2-content of approximately 40 wt%. The theoretical model includes a derivation of the free energylike potential within non-equilibrium thermodynamics for steady-state processes, a calculation of the Young's modulus of the actuator based on series-parallel schemes, similar to the Takayanagi model, and the percolation theory. The model parameters are obtained by fitting of theoretical dependencies to the experimental data. The theory and experiment are in quantitative agreement.

The study of the effect of iodine on the degradation of poly(ε-caprolactone) fibers has revealed a drastic decrease in their molecular weight upon 24 h exposure to a 10% iodine solution in ethanol. It has been assumed that the main mechanism of this degradation is alcoholysis which proceeds with an efficient rate constant of nearly 7.5 × 10–3 h–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.

Structurally variable nanoporous polylactide (PLA) films containing brilliant green (BG) as a functional antiseptic additive have been obtained by a crazing mechanism. The in vitro release of BG from the porous PLA films into a sodium phosphate buffer solution at 37 °C has been examined by spectrophotometry.

The dynamics of recovery of the open porous structure in HDPE films, which are preliminarily uniaxially deformed in the medium of supercritical CO2 followed by shrinkage in the longitudinal direction, upon their repeated stretching in air is studied by structural mechanical methods. The process of shrinkage is accompanied by the approach of lamellas and the disappearance of the oriented fibrillar structure. The value of relative shrinkage may be as high as 70–80%. According to atomic force microscopy and small-angle X‑ray scattering, these polymer films “remember” their previous strain in CO2 and in their repeated stretching in air, which is not a physically active medium, and restore the fibrillar porous structure of crazes with similar parameters. The phenomenon of such a memory makes it possible to use PE films preliminarily formed by the mechanism of intercrystallite crazing followed by their subsequent relaxation in the freestanding state as “precursors” for producing mesoporous materials with the pore volume on the order of 30 vol % for application in various fields, in particular, as vapor permeable membranes.

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.

Features of the plastic deformation of poly(p-dioxanone) fibers in air were studied. The neck propagation in the deformation speed range 0.2–15 mm/min was shown to occur in the self-excited oscillation mode. It was detected for the first time that this process is accompanied by the formation of areas with an open-pore structure. Impregnation of the fibers with brilliant green with the penetration of the die from the solution into the pores produces fibers with antimicrobial properties against the fungal culture of Candida albicans.

Experimental conditions have been established for the preparation of stable open-pore matrices with pore diameters of 10–20 nm on the basis of semicrystalline polylactide films by thedelocalized crazing mechanism. The synthesis of phosphates of calcium (brushite) and magnesium (struvite) in the pores of such a polymer matrix allows one to tune the size of the formed crystallites, which has appeared to be about 30 nm, and to obtain nanocomposites with high dispersity of the components. The resulting nanocomposites were characterized by SAXS, SEM, TGA and XRD methods.

Bioactive suture materials made of biodegradable polymers containing biologically active substances are increasingly demanded in contemporary surgical practice. Herein, the functional fibrous materials are produced by structural modification of polylactide (PLA) fibers according to the crazing mechanism in water-ethanol solutions. The threshold of ethanol concentration, at which the breaking elongation of the polymer substantially increases (up to 600-700%), is found to be 30 wt%. The crazing mechanism is employed to fill the porous structure of PLA fibers by different antiseptic substances (brilliant green, iodine, and fuchsin). PLA loaded by 0.8 wt% of brilliant green exhibits antimicrobial activity onEscherichia coliandCandida guilliermondii. The additive is released stepwise for a prolongated time period (2.5 months). The addition of 1-6 wt% iodine dramatically accelerates the polymer degradation in sodium-phosphate buffer solution at 37 degrees C. The obtained filled fibers may possess great interest for producing suture materials with prolonged action of functional components and variable degradation times.

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.

Hydrolytic degradation of porous polylactide (PLA) films with various porosity and morphology has been thoroughly investigated. It has been found that the structural and mechanical modification of PLA films by the environmental crazing mechanism results in the formation of a porous structure, is accompanied by the change in molecular-weight characteristics of the polymer and affects the localization and rate of its hydrolytic degradation. After the films were exposed in phosphate-buffered saline solution at 37 degrees C for 6 weeks, their average molecular weights M-W and M-N decreased by 1.5-2 and 3-5 times respectively, while their dispersity D-M increased to 4-5. For PLA films containing alternating porous crazes and nonporous bulk parts, the hydrolysis leads to the appearance of bimodal molecular-weight distribution (MWD) curves. The degradation of the polymer material localizes predominantly at the craze-bulk polymer interfaces, thereby leading to a rather rapid and significant decrease in the deformation and strength properties of the films, which eventually become brittle. For PLA films, that have completely passed to the fibrillar-porous structure during the hydrolytic degradation, the character of the MWD curves remains preserved, but they gradually widen and shift toward lower molecular weights. The destruction of similar samples occurs uniformly throughout the volume, and the changes in their structural and mechanical parameters are not so abrupt, and even after the hydrolysis for 6 weeks their strength remains at a level of 90 MPa. When the porous matrix of PLA is filled with calcium phosphate (up to 30 wt%), the degradation of the polymer material occurs predominantly in the crazes and hardly proceeds in the bulk parts. The approaches proposed using PLA as an example enable one to control the degradation processes in polymers by varying their structural and morphological characteristics and incorporating inorganic fillers, thus opening new ways to the creation of bioactive and biodegradable materials with predictable degradation times.