Polymer Science, Series A最新文献

Comprehensive thermodynamic analysis of mixing of poly(diallyldimethylammonium chloride) (PDADMAC) with water at 25°C has been performed. Isotherms of water sorption with linear and network poly(diallyldimethylammonium chloride) have been measured by means of interval sorption. Enthalpy of dilution of solutions of linear poly(diallyldimethylammonium chloride) and enthalpy of swelling of network poly(diallyldimethylammonium chloride) have been measured over the entire composition range by means of isothermal calorimetry. Concentration dependences of the Gibbs energy of mixing and enthalpy of mixing of poly(diallyldimethylammonium chloride) with water have been computed. It has been shown that these thermodynamic functions are negative over the entire range of composition of the solution and swollen hydrogel. The experimental data have been used in thermodynamic modeling of the interaction process, accounting for different contribution to the thermodynamic functions of mixing of poly(diallyldimethylammonium chloride) with water. It has been shown that the thermodynamic of mixing is predominantly affected, on one hand, by the molecular interaction described in the scope of the Flory–Huggins theory and, on the other hand, by the nonequilibrium disruption of glass structure of the polymer during formation of the solution and swelling of the gel. The modeling has given the values of the Flory–Huggins parameter: –0.05 ± 0.02 for aqueous solution of linear poly(diallyldimethylammonium chloride) and 0.20 ± 0.01 for hydrogel of network poly(diallyldimethylammonium chloride). Basing on the model parameters, individual contributions into the enthalpy, Gibbs energy, and entropy of mixing of poly(diallyldimethylammonium chloride) with water have been calculated.

The interaction of pectin and arabinogalactan macromolecules in aqueous solutions has been studied. It is shown that polymer complexes are formed due to hydrogen bonding between macromolecules. Crosslinking of the polymer complex by Са²⁺ ions leads to the formation of hydrogels whose properties are considerably determined by the content of arabinogalactan. At low concentrations of Са²⁺ ions (from 0.05 to 0.15 wt %), the introduction of arabinogalactan contributes to an increase in shear modulus and crosslink concentration and results in a reduction in polymer network sizes compared with hydrogels based on native pectin. With increasing arabinogalactan content the contribution of Fick’s diffusion to swelling of the synthesized hydrogels grows.

An alginic acid derivative containing amide and amino groups was synthesized by adding ethylenediamine to the carboxyl groups of the polysaccharide activated by carbodiimide. Our analysis of its structure using NMR spectroscopy confirms that the addition of ethylenediamine occurs with the formation of an amide bond and the appearance of free primary amino groups in an equimolar ratio. Using the methods of rotational and capillary viscometry in combination with dynamic light scattering and potentiometric titration, it was shown that the critical concentration for the transition to the solution mode with Ce entanglements correlates with the degree of substitution and the change in the zeta potential of the modified polysaccharides. The latter are characterized by a lower Ce concentration and, on average, a lower activation energy for the viscous flow of solutions than sodium alginate. In the pH range 6.5–6.0 for semi-diluted solutions of modified polysaccharide and sodium alginate, an oppositely directed change in the size of macromolecular aggregates is observed. The hemocompatibility of the modified polysaccharide was studied in vitro in tests of blood recalcification time, activated partial thromboplastin time, and platelet aggregation. It was shown that the modified polysaccharide does not affect blood coagulation (at concentrations of 0.033 and 2.22 mg/mL), plasma coagulation (at concentrations up to 0.0465 mg/mL), and platelet aggregation (at concentrations up to 0.182 mg/mL).

The possibility of using water-soluble heteronuclear metallamacrocyclic complexes of Sr(II)–Cu(II), Ca(II)–Cu(II), and La(III)–Cu(II) as crosslinking agents for alginate hydrogels has been investigated for the first time. The possibility of ion-induced crosslinking of alginate with metallacrown cations has been experimentally demonstrated. Alginate hydrogel microspheres have been prepared via extrusion, using the metallacrowns as crosslinking agents. The degree of cross-linking of the hydrogels depends on the nature of the central element of the metallacrown. In terms of their crosslinking ability, the considered metallacrowns (MC(M)) are arranged in the following series: MC(La) > MC(Sr) > MC(Ca).

The rapid growth in the use of carbon-based composites has resulted in the need to replace commercially available carbon materials with those from renewable and sustainable sources. In this work, recovered carbon black (rCB) from the waste tire was used for the preparation of 3-dimensional (3D) chitosan/carbon composites. The rCB was treated with acid (T-rCB) to modify its functionality. By varying the percentage of T-rCB, the 3D-treated chitosan/carbon composites (C/T-rCB) were prepared via a free-drying method. The rCB sample is shown to be agglomerated and undispersed while the T-rCB could disperse homogeneously and is stable in water. The Raman bands at T-rCB had weaker intensities and thus the I_D/I_G area was less than rCB. The incorporation of T-rCB in chitosan composite shows a good interaction through the ‒CONH– bond. The increment of T-rCB in the composite was able to increase the water uptake and water retention abilities. The addition of T-rCB has resulted in improved tensile strength, especially to the 0.03 C/T-rCB. It was found the 3D composite samples were fibrous and porous.

Nucleation density is a fundamental parameter influencing the microstructure, properties, and performance of polymeric materials. Controlling and manipulating nucleation density allows for tailoring polymeric materials with specific characteristics, enabling advancements in various fields of industrial applications. The present study investigates nucleation density from an isotropic and self-nucleated melt of isotactic polystyrene (iPS). A wide range of temperatures, from 225 to 260°C are considered, and the samples are subjected to partial or isotropic melt followed by isothermal crystallization. In the case of partial melting below 230°C, the nucleation density is attributed to the seed nuclei originating from self-nucleated melts due to incomplete crystal melting. Crystallization from isotropic melts involves a limited number of heterogeneous nucleation sites activated on the surfaces, impurities, or foreign particles within the melt. On the other hand, crystallization from the glassy state was found to rely on the molecular conformation and mobility in the amorphous phase, which plays a crucial role in achieving an optimal nucleation density. The experimental findings indicate that in molten and glassy states, the predetermined active nucleus sites significantly influence the nucleation process during crystallization. The nucleation density directly affects the crystallization kinetics and morphology of crystals. A higher nucleation density leads to a more significant number of smaller crystals, resulting in a finer microstructure. This can have significant implications for polymer properties such as mechanical strength, optical transparency, electrical conductivity, permeability, and thermal properties.

The collision of drops of water and elastic liquids with a thin cylinder (fiber) has been studied. Aqueous solutions of polymers were used as elastic liquids, which simulated the rheological behavior of oral fluid—the main carrier of infections by airborne drops. Water as a Newtonian fluid was investigated to identify the elastic effects when comparing the collisions of Newtonian and non-Newtonian fluids—water and polymer solutions. The flight path of the drop and the cylinder axis are mutually perpendicular. Attention is focused on the difference between the collisions of water drops and drops of elastic liquids. In the experiments, the diameter of the drop was 3 mm, and the diameter of the horizontal stainless-steel cylinders was 0.4 and 0.8 mm. Drops were formed by the slow flow of liquid from a vertical stainless-steel capillary with an outer diameter of 0.8 mm, from which the drops were periodically separated under the influence of gravity. The velocity of the drop before the collision was determined by the distance between the end of the capillary and the target (cylinder); in the experiments, this distance was 5, 10, and 20 mm. The velocities of falling drops before impact were estimated in the range of 0.2–0.5 m/s. The collision process was monitored using high-speed video recording methods with frame rates of 240 and 960 Hz. Water and aqueous solutions of polyacrylamide with a molecular weight of 11 million and concentrations of 100 and 1000 ppm were used as test liquids. Experiments have shown that, depending on the height of the drop and the concentration of the polymer, various drop collision scenarios are possible: (1) short-term rebound of the drop from an obstacle, (2) braking and stopping the drop on the obstacle, (3) flow of the drop around a cylindrical obstacle while maintaining continuity and continuing free flight, (4) disintegration of the drop into two secondary drops, each with its own history of subsequent flight.

Ceramic/polymer composites exhibit high dielectric constant, low dielectric loss, and high energy storage density. In this work, the characteristics of the spin-coating process to obtain a thin and uniform composite film without obvious defects were used to prepare composite films BaTiO₃/PVDF. High-quality composite films enable better study of their macro- and microstructures, dielectric and energy storage properties. The results show that the BaTiO₃/PVDF composite films prepared by the spin-coating process exhibit good uniformity in both macroscopic and microstructure. The average thickness is about 7 μm. At the same frequency, the dielectric constant increases with the increase in BaTiO₃ content. The dielectric constant of 30 vol % PVDF composite film reached 62 at 100 Hz, which was nearly 6.8 times higher than that of pure PVDF. In addition, the dielectric loss of the composite film first decreased and then increased with the increase of frequency. With increasing of the BaTiO₃ content, the breakdown strength of the composite film decreased. The P_max and U_charge of the composite film increased with increasing of the electric field. The P_max of 30 vol % composite film was 4.41 μC/cm² at 900 kV/cm_. The energy storage density of 15 vol % composite film was 6.916 J/cm³ at 1500 kV/cm.

The rheokinetics of gelation of poly(vinyl alcohol) aqueous solution systems with chemical crosslinks and physical junctions, including hybrid ones, has been studied. Hydrogels are obtained using glutaraldehyde and/or tetramethoxysilane as crosslinking components. It has been shown that at the initial step of gelation (until the systems reach critical gelation conversion) the efficiency of the process is determined by the concentration of the crosslinking agent rather than the chemical nature of network crosslinks. A comparative analysis of the mechanical properties of chemical, physical, and hybrid hydrogels at various temperatures is performed. Quasi-static uniaxial compression and tension tests make it possible to establish the contribution of network junctions and crosslinks to the behavior of hybrid hydrogels and their distinctive features.

In recent years, plastic waste has been a major cause of environmental pollution, negatively affecting human health and the ecosystem. Therefore, the trend of using bioplastics to replace fossil-based plastics has been becoming important and popular. This study aimed to successfully prepare a starch-based bioplastic film. Starch was extracted from avocado seeds using wet soaking method. The mechanical properties of bioplastic film were enhanced by reinforcing with nanocellulose fibers (CNFs) with using glycerol as a plasticizer. The results from the Scanning Electron Microscopy (SEM) analysis showed that the surface of the bioplastic film was affected by the content of used CNFs. The micro size aggregations occurred when too much CNFs was added to the starch matrix. The Infrared spectroscopy (FTIR) results presented peaks at wavenumbers corresponding to vibrations of hydroxyl, methyl, carboxyl and ether groups, which were characteristic peaks for the chemical structure of starch and CNFs. The crystallinity of bioplastic films tends to increase when CNFs was added to the starch matrix. The mechanical properties analysis of bioplastic films showed that CNFs were dispersed well in bioplastic films leading to the enhanced mechanical properties of the films.