Evidence from Thermal Aging Indicating That the Synergistic Effect of Glyoxal and Sodium Sulfite Improved the Thermal Stability of Conformational Modified Xanthan Gum

Xanthan gum is prone to thermal oxidative degradation, which limits its applications. However, conformational changes in xanthan gum and appropriate stabilizers may improve its thermal stability. Therefore, in this study, we aimed to establish a strategy to maintain the viscosity of xanthan gum during long-term storage at high temperatures. We modified the original strain used for xanthan gum production by genetic engineering and added stabilizers during the production process. The structure and thermal stability of the resulting xanthan gum samples were then determined. Pyruvyl deficiency, combined with the addition of sodium sulfite and glyoxal during the production process, was found to significantly improve the maintenance of viscosity. The apparent viscosity of the new xanthan gum solution remained above 100 mPa·s after being stored at 90 °C for 48 days. Fourier-transform infrared spectra and scanning electron microscopy images showed that pyruvate-free xanthan gum with added stabilizers had more extensive cross-linking than natural xanthan gum. In conclusion, these findings may contribute to the use of xanthan gum in applications that require high temperatures for a long period of time.

Morphology and Tensile Properties as a Function of Welding Current in Thermoplastic Induction Welds

Compared to other conventional joining methods, induction welding offers the superiority of avoiding mechanical degradation and satisfying the need for weight reduction in the aircraft industry. In this paper, a metal mesh was adapted as an induction component in the induction welding of polyetheretherketone (PEEK) with various currents. The effect of welding current on the microstructure and mechanical properties of the induction welding joint was further investigated. The results indicate that induction welding joints with the narrow thickness of the fusion zone and high tensile strength can be attained in the welding current range of 7.05 A to 11.05 A. However, when the current exceeds 13.91 A, the excessive heat input leads to the unsteady flow of PEEK or even thermal oxidative degradation and thermal decomposition, which increases the thickness of the fusion zone and reduces the tensile strength of the joint. In addition, the principal fracture mode presents cohesive failure, thereby promoting the tensile strength of the joint.

ПІДВИЩЕННЯ ВОГНЕЗАХИСНОЇ ЕФЕКТИВНОСТІ ІНТУМЕСЦЕНТНИХ ЕПОКСИДНИХ ПОКРИТТІВ СПОЛУКАМИ ІНТЕРКАЛЬОВАНОГО ГРАФІТУ

Investigation of the effect of nitrate oxide graphite on the parameters of char layer, obtained from the system of ammonium polyphosphate / melamine / pentaerythritol / epoxy resin under the influence of temperatures of 200–800 °С. Methodology. A fire retardant mixture was chosen as a model intumescent system ammonium polyphosphate / melamine / pentaerythritol. As a polymer component was used bisphenols A / F epoxy resin together with a polyamidoamine hardener. Nitrate oxide graphite was obtained by oxidation of natural scaly graphite with fuming nitrogen acid. The effect of impurities of nitrate oxide graphite was determined by thermogravimetry on the intumescence coefficient of intumescent compositions and the mass of the char residue intumescent compositions in temperature range of 200–800 °С. Findings. The influence of nitrate oxide graphite on the characteristics was studied of char layer of epoxy intumescent system ammonium polyphosphate / melamine / pentaerythritol / epoxy resin. The study of thermal oxidative degradation was carried out intumescent compositions in the temperature range 200–800 °С. It was shown that intercalated graphite compounds increase the thermal stability of the formed char layer at temperatures > 600 °С. Determined intumescence coefficients and thermogravimetric analysis of modified intumescent systems was performed nitrate oxide graphite with different degrees of intercalation, in the conditions of 200–800 °С. It was established that the optimal parameters of the char layer are in terms of volume intumescence coefficient and mass of the char residue are provided by graphites, which contain 15–25% of intercalant in its composition. But the results obtained allow us to determine nitrate oxide graphite as a promising modifier of epoxy intumescent systems to increase its fire protection efficiency. Originality. The influence of degree of intercalation of nitrate oxide graphite was studied on the characteristics of char layer of epoxy intumescent system for the first time. Practical value. The optimal content of intercalant in nitrate oxide graphite was established for the development of formulations of intumescent epoxy coatings with increased fire retardant properties.

Enhancing Chain Mobility of Ultrahigh Molecular Weight Polyethylene by Regulating Residence Time under a Consecutive Elongational Flow for Improved Processability

Improving the processability of ultrahigh molecular weight polyethylene (UHMWPE) and understanding the effect of the polymeric chain mobility has long been a challenging task. Herein, we show that UHMWPE without any processing aids can be processed at a lower temperature of 180 °C compared to conventional processing temperatures (~250 °C) under a continuous elongational flow (CEF) by using an eccentric rotor extruder (ERE). By probing the effect of the residence time of UHMWPE samples under a CEF on the morphology, rheological behavior and molecular orientation, we find that the long polymer chains of UHMWPE are apt to orientate under a consecutive volume elongational deformation, thereby leading to a higher residual stress for the extruded sample. Meanwhile, the residence time of samples can regulate the polymeric chain mobility, giving rise to the simultaneous decrease of the melting defects and residual stress as well as Hermans orientation function with increasing residence time from 0 to 60 s. This also engenders the enhanced diffusion of UHMWPE segments, resulting in a defect-free morphology and higher entanglement with lower crystallinity but without causing obvious thermal oxidative degradation of UHMWPE. This interesting result could originate from the fast chain entanglement and particle welding enabled by a desirably short residence time, which could be explained by the empirical, entropy-driven melting explosion mechanism.

ERBIUM AND SANDWICH-TYPE LUTETIUM COMPLEXES CONTAINING FRAGMENTS OF TETRAANTHRACHINOPORPHIRAZINE AND SUBSTITUTED PHTHALOCYANINES

The present work relates to the synthesis and spectral properties of erbium and sandwich type metal complexes containing tetraanthraquinoporphyrazine as well as phthalocyanine fragments. By reacting tetraanthrachinoporphirazine erbium (lutetium) acetate with excess phthalonitrile, 4-chloro, 4-bromophthalonitrile and unsubstituted phthalonitrile, sandwich-type complexes of an unsymmetrical structure were obtained. The compounds were extracted from the reaction mixture with a suitable organic solvent (DMF or toluene) and purified by prolonged extraction of impurities with acetone in a Soxlet apparatus. Final purification was carried out by column chromatography. The obtained complexes are green solids having solubility in DMSO, DMF, and concentrated sulfuric acid. The composition and structure of complexes were confirmed by elemental analysis, IR and electron spectroscopy. Influence of chemical structure of new "sandwich" compounds on their spectral properties and possible applications has been investigated. In particular, when analyzing the electron absorption spectra, it was found that the metal, the nature of the substituents in the tetraanthraquinone moiety and the replacement of hydrogen atoms with halogen atoms in the phthalocyanine moiety slightly affect the nature and position of the absorption maxima. Studies have been carried out on the coloristic properties of synthesized organosoluble metal complexes erbium and lutetium. The compounds have been found to exhibit the properties of pigments and dyes for polymeric materials such as polystyrene and polyethylene. The temperature parameters of thermal oxidative degradation were determined and it was found that the obtained "sandwich" type phthalocyanines have high resistance to thermal oxidative degradation.