RESUMEN
This article is devoted to the development of new photostabilizers for polylactide (PLA), a polymer that is an environmentally friendly alternative to polymers and is based on fossil raw materials. We have elucidated the role of the reaction center of two potential PLA photoprotectors: N-isobornylaniline and 2-isobornylphenol, in reactions occurring in a polymer matrix under the action of UV-C radiation. PLA samples with the photostabilizers were irradiated under a wavelength of 253.7 nm for 4, 8 and 12 h. The effectiveness of the photostabilizers was evaluated based on FTIR spectrometric data, 1H and 13C NMR, scanning electron microscopy and simultaneous thermal analysis (TG-DSC). Both stabilizers led to the protection of ester bonds between monomer units of PLA. However, 2-isobornylphenol proved to be more effective at a concentration of 0.05 wt.%, while the optimal concentration of N-isobornylaniline was 0.5 wt.% by weight. TG-DSC showed that the addition of N-isobornylaniline led to an increase in PLA resistance to thermal decomposition; the temperature of the onset of weight loss increased by 2.8 °C at 0.05 wt.% and by 8.1 °C at 0.5 wt.% of N-isobornylaniline. The photoprotector 2-isobornylphenol, on the contrary, reduced the thermal stability of PLA.
RESUMEN
Eu-doped bismuth-based Bi1.5M0.4Mg0.5Nb1.5O7-δ (M = Li and Na) pyrochlores were synthesized by the organic-inorganic precursor combustion technique. The study examined the effect of rare earth element Eu3+ doping on the structural, dielectric, optical, and luminescence properties of synthesized materials. The analysis showed that the substitution of Bi3+ cations with Eu3+ leads to dielectric permittivity decreasing due to the structural distortion for the Eu-concentrated compositions and low polarizability of Eu3+. The band gap values predicted by electronic band structure calculation using DFT-HSE03 are in line with the experimental ones and tended to increase with the decrease in the unit cell parameters with Eu concentration changing. By the optical and luminescence measurements, the specific roles of Li- and Na-containing host types, additional phases, and dopant concentration in bismuth niobate pyrochlores are shown concerning the dielectric, structural, and Eu3+ emission properties. All Eu-doped bismuth-based pyrochlore ceramics behave as high-frequency dielectrics up to 200 °C and have mixed conductivity (electronic, proton, and oxygen) at T > 200 °C. The obtained dielectric parameters make them suitable for high-frequency ceramic capacitors.
RESUMEN
The aims of this research were to obtain modified pectins of callus cultures using various culture conditions, to evaluate the relationship between the chemical characteristics of pectins, the swelling behavior and the release of prednisolone from calcium pectinate gel (CaPG) beads. An increase of the calcium concentration in the culture media correlated significantly with the rhamnogalacturonan I (RG-I) branching of the pectin. The beads from the pectin with a higher RG-I branching had the lower prednisolone release in a gastric fluid. The beads produced from the pectins obtained from callus cultured with a higher calcium concentration showed the lower prednisolone release. The swelling of the CaPG beads from pectin with a lower molecular weight (Mw) or linearity occurred to a lower degree. All beads prepared from modified pectins showed a high stability and a slow liberation of prednisolone in the simulated gastric and intestinal fluids, whereas rapid drug release in a colonic fluid. An applied strategy involving modification of the pectic structure using the abiotic factors allows obtaining the pectic gels with modified functional properties, in particular, with enhanced gastric and small intestinal resistance and a low drug release. These CaPG beads can be applied as the carriers for colon delivery of the drugs.
