Polymer Science, Series A最新文献

The effect of the surroundings on stress and temperature self-oscillations during stretching of polyethylene terephthalate films has been studied. The tests were carried out in air, helium, and sulfur hexafluoride. Spontaneous acceleration of plastic flow is due to the conversion into heat of elastic energy stored by the specimen during stretching. It has been shown that an increase in the thermal conductivity coefficient of the gas leads to an increase in the average stress and oscillation amplitude and a decrease in the oscillation frequency. These changes are explained by an increase in heat transfer and, accordingly, a decrease in the temperature of the polymer flow zone. A decrease in the film thickness leads to an increase in the heat transfer to heat release ratio, which is similar to an increase in the heat transfer coefficient.

The films with various orientation degrees were produced by polyvinylidene fluoride (PVDF) melt extrusion. The crystalline structure of the oriented films was studied using wide-angle X-ray scattering. The relaxation processes within the temperature range of 273–333 K were investigated using thermally stimulated depolarization (TSD) method. Within examined temperature range, two relaxation processes were observed, which are assumed to be associated with dipolar-segmental motion. The intensity of these relaxation processes declined as the degree of orientation increased. In order to study the influence of crystallinity degree on the observed relaxation processes, the extruded PVDF films were subjected to isometric annealing. It was observed that an increase in the crystallinity degree leads to the growth of thermally stimulated depolarization intensity in the temperature range of 300–310 K and its decrease in the temperature range of 280–290 K.

In this study, the possibility of using hyaluronic acid (HA) modified lutein as the main component of eye drops for ophthalmic treatment was discussed. Firstly, hyaluronic acid grafted lutein (HA-g-lutein) was synthesized by hydrophilic modification of lutein by Steglich esterification. The grafted copolymer was self-assembled in water to form micelles and then loading unreacted lutein to prepare composite nanoparticles (denoted HA-lutein NPs). The findings from the FTIR, UV–Vis, and XRD analyses indicate that the graft copolymers were synthesized while preserving the structural integrity of lutein. Furthermore, the modification demonstrated efficient inhibition of lutein crystallization. TEM showed that HA-lutein NPs self-assembled into spherical micelles in water, the particle size of which was on the nanometer scale. The saturation solubility of HA-lutein NPs exhibits a 48-fold increase compared to that of free lutein. Then the cytotoxicity of HA-lutein NPs and the effect on in-vitro transcorneal permeation of excised-rabbit cornea, corneal hydration level, and in-vivo ocular irritation after topical administration of HA-lutein NPs in rabbit eyes were studied. The results indicated the ocular safety of HA-lutein NPs. The quantitative analysis of permeability parameters by HPLC showed that the apparent permeability coefficient and the cumulative penetration quantity within 360 minutes of the HA-lutein NPs group were 3.71 and 7.04 times higher compared to the free lutein group. In summary, the graft modification of lutein with HA to form nanoparticles is an effective method to improve the availability of lutein in the eye and has potential application in ocular therapy.

The study exlores the possibility of using organomineral complexes, obtained as a result of adsorption of the macromolecular biocides (polyguanidines) on the montmorillonite surface, to protect composites based on plasticized polyvinyl chloride from photooxidative degradation and biofouling. According to UV spectro-scopy data and the results of measurements of the intrinsic viscosity of polymer solutions, it has been found that the introduction of organomineral complexes into the material helps to reduce the extent of photooxidative degradation of the material under conditions of hard UV irradiation. The organomineral complexes used effectively suppress the fouling of the composites by biofilms of the micromycete Yarrowia lipolytica 367-3. The mechanical characteristics of composites containing organomineral additives are maintained at a high level after thermal aging (in accordance with the technical documentation for the material). The composites also meet the technical documentation requirements for weight loss on heating, density, and volume resistivity, but increasing the concentration of the organomineral additive in the composite above 2 wt % leads to an increase in water absorption of the material above required values.

This study aimed to understand the impact of different concentration routes on the structure and properties of silk sericin (SS) films. Sericin was extracted from defective cocoons (DC), at high temperature and pressure (HTHP) using an autoclave. The obtained aqueous solution was concentrated using three different routes until a final concentration of 2% (w/v) was reached. These routes include freeze-thawing (SS_FT), rotary evaporation (SS_E), and the dissolution of spray-dried SS in distilled water (SS_SD). Films were formed from the three solutions obtained, which were characterized by Fourier transform infrared spectro-metry (ATR-FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC), and their water absorption capacity and non-soluble fraction were evaluated. According to the FTIR and TGA results, the samples concentrated by evaporation or using spray-dried SS exhibited a more amorphous and lighter structural conformation than those found in F-SS_FT. This finding suggests that the use of high temperatures for SS concentration promotes protein degradation and the formation of less ordered structures in SS films. The structural properties of the SS films were confirmed by the water absorption results. In particular, the major presence of crystalline structures in F‑SS_FT seems to limit their affinity for water, favoring the non-soluble fraction in this sample. The marked effect of the concentration method on the structure and properties of SS films highlights the potential of this process in the design of more efficient manufacturing routes for SS-based materials that exhibit a distinctive performance.

The current work presents the fabrication of polyaniline (PAni)/polyvinyl alcohol (PVA) nanofiber composites through electrospinning. The morphological properties of the sample evaluated by employing the field emission scanning electron microscope (FESEM) and the diameters of the samples are between 141 to 234 nm. The presence of both PVA and PAni in the nanofiber structure was evaluated with the aid of Fourier-Transformation Infrared Spectroscopy (FTIR). When a rifampicin-doped PVA film and a rifampicin-doped nanofiber PAni/PVA film were irradiated with a continuous wave laser beam at a wavelength of 532 nm, diffraction ring patterns (DFRPs) were seen. The nonlinear refractive index (NLDX) ({{n}_{2}}), was determined from the number of observed rings. Large value obtained of the order of 212.48 × l0^–8 cm²/W for PAni/PVA nanofiber composites. The change in the nonlinear refractive index (Delta n), depends primarily on both the natural refractive index of the material and the NLDX, in which diffraction patterns play a major role in this change. In addition to that, the optical limiting) ({text{OPT}}) (qualities were investigated. Within a solid PAni/PVA host, the dye shows of some impressive optical limiting features. It has been discovered that the mechanism responsible for the limitation of optical sensitivity is mostly of a thermal nature.

The separation of peptides with sequences inverted from N-terminus to C-terminus has been experimentally and theoretically investigated. Although these sequences are composed of the same amino acid residues, their adsorption properties are different. Theoretical calculations in terms of the BioLCCC peptide separation model showed that a difference in the adsorption properties of these sequences is due to a difference in the spatial correlation of chain connectivity of amino acid residues and terminal groups during their interaction with the surface.

In order to clarify the influence of processing parameters on the structure and properties of biaxially oriented polyethylene terephthalate (BOPET) films, by preparing BOPET film using a biaxial stretching film production line, the structures were characterized by means of DSC, WAXD, SAXS and the mechanical, optical, and thermal shrinkage properties were analyzed to investigate the effects of heat-setting temperature on the structure and properties of BOPET films. The results showed that with the increase of heat-setting temperature, the tensile strength in the machine direction (MD) of BOPET film decreased, while the fracture elongation and elastic modulus in the transverse direction (TD) increased. In addition, the crystallinity and long period of BOPET films increased, haze increased, and the transmittance and glossiness showed little change. However, the thermal shrinkage rates in both MD and TD decreased.

The composite hydrogel sodium graft poly(acrylic acid-co-N-isopropylacrylamide)/bentonite (SA-g-P(AA-co-NIPAM/BENT) emerges as an effective adsorbent to remove methylene blue (MB) and methyl violet (MV) from aqueous solutions through adsorption. Compared with the sodium graft poly(acrylic acid-co-N-isopropylacrylamide) graft copolymer SA-g-P(AA-co-NIPAM), the growth rate in terms of adsorption capacities of MV and MB is 35.5% (from 310 to 420 mg/g) and 10.2% (from 293 to 323 mg/g), respectively, with an incorporation of 0.6 g of BENT. The adsorption of MB on SA-g-P(AA-co-NIPAM/BENT) is spontaneous while MV is nonspontaneous. In addition, adsorption of both dyes satisfies the Freundlich equation and the Pseudo second-order kinetic model.