Polymer Science, Series C最新文献

The introduction of hydrophilic fillers in the matrix of hydrophobic thermoplastic polymers is a complicated issue, due to thermodynamic incompatibility of the components and poor adhesion properties. These complications are the most pronounced in the case of a hydrophilic polymer which cannot melt without decomposition (as polysaccharides) used as the filler. In this study, we have taken advantage of the solvent-free extrusion method both to modify the chitosan chemical structure in order to impart amphiphilic properties and to mix the obtained derivatives with polyethylene. The influence of the processes parameters, the presence of plasticizer, and the filler content on the thermal and mechanical properties of the composite film materials as well as their morphology has been investigated. It has been found that the introduction of hydrophobic fragments in the structure of chitosan insignificantly improved the mechanical properties of the materials in comparison with the pristine polysaccharide. A more significant effect has been caused by simultaneous introduction of the plasticizer, affording the materials with uniform morphology and improved plasticity.

The review provides information about the initial and modern phases of creating methods and stages of technologies for producing powdered cellulose, as well as microfibrillar, microcrystalline, and nanocellulose. The raw materials for powdered cellulose are waste from the woodworking and agricultural industries, as well as processed products from the pulp, paper, and textile industries. Historically established mechanical, physical, chemical, and biological methods are presented in the review with information on the possibilities of using additional stages, for example, the steam-explosive method. Information is provided on comparative structural studies of the presence of functional groups of lignocellulosic raw materials and powdered celluloses obtained from them, taking into account the supramolecular structure and residual lignin. It is shown that powdered cellulose can be widely used in sovereign technologies of the pharmaceutical and cosmetic industries as binders and emulsifiers and can be processed into ethers and esters, as well as into fibers (through solutions). Nonaqueous solutions of cellulose and mixtures of cellulose with synthetic polymers open up the possibility of creating carbon fiber materials and composites (uniquely combining high strength, chemical and heat resistance, as well as electrical conductivity and low density), which are important in scientific and practical terms in expanding the range of products of the textile and medical industries, as well as a variety of equipment with unique properties for the automotive industry, rocket and missile engineering, and various special-purpose equipment. The development of these technologies is, of course, interdisciplinary.

On the basis of furfuryl glycidyl ether, the product derived from furfural, diol chain extenders have been synthesized. Using these chain extenders and bismaleimide as a crosslinker polyurethanes with thermally induced self-healing effect have been prepared by the reversible Diels–Alder reaction. The structure of the synthesized polymers is studied by IR spectroscopy. Thermal and physicomechanical properties of the materials are also investigated. Differential scanning calorimetry measurements revealed the cyclic nature of direct and retro-Diels–Alder reactions. Visual assessment of the self-healing ability of the material is carried out using scanning electron microscopy. Quantitative evaluation (the self-healing efficiency of the Young’s modulus and strength) is performed by means of dynamometric analysis of initial and recovered polymer samples. It has been demonstrated that the content of dynamic bonds affects the properties of polyurethanes, as well as the efficiency of self-healing.

Processes of polymer modification in a supercritical carbon dioxide environment leading to the production of new materials intended primarily for medicine, pharmacology, and conducting polymer systems are analyzed. The processes of polymer impregnation in a supercritical carbon dioxide environment with carbon nanotubes to produce heat- and electrically conductive polymer materials and the processes of polymer micronization used in the development of polymer–polymer composite materials are considered. The processes of obtaining aerogel materials based on polysaccharides (sodium alginate) for use as matrices for biocompatible heterogeneous catalytic systems, the processes of impregnation of thermoplastics with photochromic and luminescent compounds leading to the corresponding photoactive polymer materials, and the processes of immobilization in natural polysaccharide matrices of biologically active compounds allowing the production of prolonged medicinal products are described. Particular attention is paid to the features of graft copolymerization, which allows obtaining biocompatible products for additive technologies and completely nontoxic materials with high adhesion to cells.

Composite materials with a two-layer coating consisting of ultrahigh molecular weight PE and a lower molecular weight PE are synthesized on the surface of filler particles (Al₂O₃/ultrahigh molecular weight PE/lower molecular weight PE) using the polymerization filling technique by the sequential two-step polymerization of ethylene. In the composites, the ratio ultrahigh molecular weight PE : lower molecular weight PE (polyethylene) is varied with the molecular weight of PE being constant or the molecular weight of PE is varied with the ratio ultrahigh molecular weight PE : lower molecular weight PE being constant. In this case, the lower molecular weight PE is the external layer on the surface of composite particles, while the ultrahigh molecular weight PE occurs directly on the surface of filler particles. In both cases, with an increase in the fraction of polyethylene in the two-layer coating in pressed composites, the degree of crystallinity increases and the lamella parameters change. The mobility of polymer chains in the intercrystalline amorphous layer alters. Creation of two-layer coatings ultrahigh molecular weight PE/lower molecular weight PE allows modification of the deformation–strength properties of the composites. An increase in the content of polyethylene in the composites is accompanied by a considerable increase in the elongation at break and the elastic modulus of the composites while the breaking stress decreases.

Morphology of reactor polymer compositions based on ultrahigh molecular weight polyethylene (UHMWPE) with M_w = 1000 kg/mol and low molecular weight high density polyethylene (LMWPE) with M_w = 48 kg/mol obtained in single-stage ethylene polymerization in the presence of a binary catalytic system is studied. The content of the LMWPE fraction in the compositions ranged from 6.3 to 29 wt %. Melting and crystallization temperatures, the content of the crystal phase for these materials were determined using the DSC method. The data obtained indicated the probability of the formation of co-crystals between segments of macromolecules in UHMWPE/LMWPE compositions. A study of nascent UHMWPE/LMWPE by the WAXS analysis in wide angles was carried out to determine the effect of the content of the LMWPE fraction on the crystalline phase of the materials, the dimensions of the lamellae in the directions perpendicular to the planes 110 and 200. The study and comparison of the viscoelastic properties of UHMWPE, LMWPE and reactor compositions based on them by the DMA method revealed the modifying effect of the LMWPE fraction on the crystalline and amorphous phases of UHMWPE/LMWPE compositions.

The review is devoted to the analysis of the areas of practical application of polymer waste in the composition of building materials, in particular, in polymer-filled concretes, polymer concretes, in road coatings, and in wood-polymer composites. The choice of these materials is due to the large tonnage of their production, demand, and long service life.

A brief review of research initiated by works carried out earlier under the guidance of N.S. Enikolopov on the production of composite materials based on polypropylene and nanocarbon fillers by in situ polymerization is provided. The data on the mechanical, thermal, and electrical properties of the resulting materials are presented. The structure and concentration of nanofillers, as well as the structure of polypropylene (iso-, syndio-, and stereoblock), have a significant impact on the characteristics of the composites. The introduction of carbon nanofillers into the polypropylene matrix leads to a noticeable increase in the thermal and thermo-oxidative stability of the material. The prospects for using nanocomposites based on polypropylene and nanotubes and graphene nanoplatelets to develop shields and absorbers of electromagnetic radiation are considered. It has been shown that the modification of polypropylene properties by introducing various types of carbon nanofillers using in situ polymerization makes it possible to design novel functional composite materials with a valuable set of properties.

Academician N.S. Enikolopov’s method of mechanochemical solid-phase modification of polymers under conditions of intensive shear deformation has resolved one of the most important issues in cellulose processing, its dissolution. The resulting method of solid-phase dissolution in N-methylmorpholine Nрoxide (MMO) has afforded highly concentrated solutions of cellulose and a series of synthetic polymers, as well as mixed solutions based on them in a wide range of concentrations. It has been shown for the first time that the highly concentrated phase (cellulose concentration up to 45%) formed during phase separation in the presence of a precipitant undergoes a transition into nonequilibrium columnar mesophase state. The addition of synthetic polymers, which form crystal solvates with MMO but do not interact with cellulose, to solutions of cellulose in MMO shifts the columnar mesophase formation process into equilibrium. The resulting composite fibers have exhibited high strength and deformation properties. The mechanisms of interaction of various types of polymers with MMO, as well as these between cellulose and the polymers with MMO, at different stages of the mixed compositions preparation (from solid-phase mechanical activation during shear deformation to the transition into a fluid state and spinning) have been elucidated. The performed experiments have made it possible to identify the directions for targeted tuning of cellulose structure and properties, as well as the fabrication of compositions based on it.