Molecular Simulation on the Thermal Stability of Meta-Aramid Insulation Paper Fiber at Transformer Operating Temperature

Molecular dynamics study on structural modulation and dyeing property optimization of meta-aramid in a DMSO/electrolyte system

Meta-aramid (PMIA) fabrics are typically problematic to dye owing to their extremely crystalline structure and high compactness. Herein, Dimethyl sulfoxide (DMSO) and electrolyte as hydrogen bond regulators were selected to improve the dyeability of PIMA dyed with cationic dyes. The PMIA shows both high dyeing and mechanical properties as a result of the synergistic effect of DMSO and electrolyte in the system, which destructs hydrogen bonding networks and increase interaction energy density between dye molecules and PMIA, confirmed by a series of characterization and molecular dynamics simulations. In the DMSO/NaCl/PMIA system, while maintaining excellent mechanical (breaking strength and elongation at break of 24.6Mpa and 37.6 %, respectively) and thermal properties, PMIA not only obtained the best dyeability, increasing the Dye uptake from 20 % to 70.62 % and the K/S value from 2.92 to 18.02, but also achieved excellent colour fastness (fastness to dry and wet rubbing, fastness to light, and fastness to washing of 4-5, 3-4, 3-4 and 4-5, respectively). Simulated results and experimental data verified that the DMSO/NaCl system optimally synergizes hydrogen bond regulation for PMIA and achieves the best dyeing effects for cationic dyes, manifesting its great potential in the PMIA wearability area.

Related factors of perioperative low body temperature and incidence of postoperative shivering in patients undergoing complex percutaneous nephrolithotomy and the effect analysis of composite insulation nursing intervention

This study aimed to analyze the factors associated with intraoperative hypothermia and postoperative shivering rates in patients undergoing complex percutaneous nephrolithotomy (PCNL) and investigate the effects of combined insulation nursing intervention. A total of 168 patients were included, with 103 patients in the control (Ctrl) group receiving routine care and 65 patients in the nursing (Nur) group receiving combined insulation nursing intervention measures. General information, surgical data, temperature, intraoperative hypothermia incidence, postoperative shivering, and complication rates were statistically analyzed between the two groups. Patient temperature, blood pressure, and blood gas indicators including pH value, bicarbonate, and lactate levels were recorded at admission (T0), before anesthesia (T1), 30 min after spinal-epidural combined anesthesia (T2), 60 min (T3), 90 min (T4), 120 min (T5), and postoperatively (T6). The results demonstrated that the average intraoperative temperature of patients in the Nur group was significantly higher than that of the Ctrl group (P < 0.001), and their incidence of hypothermia was significantly lower than that of the Ctrl group (P < 0.01). Additionally, the Nur group exhibited shorter recovery time (18.36 ± 3.58 min), extubation time (28.01 ± 3.12 min), and length of hospital stay (8.45 ± 2.14 days) compared to the Ctrl group (P < 0.05). The incidence of postoperative shivering was 4.62 %, significantly lower than that of the Ctrl group (P < 0.001). Multifactorial analysis revealed that age ≥60 years, stone diameter ≥3.0 cm, irrigation volume ≥3000 mL, nursing intervention measures, and surgical duration were the main factors influencing the occurrence of intraoperative hypothermia. Age ≥60 years, nursing intervention measures, surgical duration, and intraoperative temperature<36 °C are identified as major risk factors for postoperative shivering. This indicates that specialized nursing care and combined insulation nursing intervention measures in patients undergoing complex percutaneous nephrolithotomy contribute to reducing the incidence of intraoperative hypothermia and postoperative shivering. It is recommended to promptly address the risk factors associated with hypothermia and shivering during and after surgery to mitigate the risk of perioperative complications.

Hydro-Sensitive, In Situ Ultrafast Physical Self-Gelatinizing, and Red Blood Cells Strengthened Hemostatic Adhesive Powder with Antibiosis and Immunoregulation for Wound Repair

Immediate and effective hemostatic treatments for complex bleeding wounds are an urgent clinical demand. Hemostatic materials with characteristics of adhesion, sealing, anti-infection, and concrescence promotion have drawn growing concerns. However, pure natural multifunctional hemostatic materials with in situ ultrafast self-gelation are rarely reported. In this study, a hydro-sensitive collagen/tannic acid (ColTA) natural hemostatic powder is developed that can in situ self-gel to form adhesive by the non-covalent crosslinking between tannic acid (TA) and collagen (Col) in liquids. The physical interactions endow ColTA adhesive with the characteristics of instantaneous formation and high adhesion at various substrate surfaces. Crucially, ColTA powder adhesive shows an enhanced adhesion performance in the presence of blood due to the electrostatic interactions between ColTA adhesive and red blood cells, conducive to effective in situ sealing and rapid hemostasis. The biocompatible and hemocompatible ColTA adhesive can effectively control bleeding and seal the wounds of the caudal vein, liver, heart, and femoral arteries in rats. Furthermore, the low-cost and ready-to-use ColTA adhesive powder also possesses good antibacterial and inhibiting biofilm formation ability, and can efficiently regulate immune response by the NF-κB pathway to promote wound repair, making it a highly promising hemostatic material with great potential for biomedical applications.

Self-Reinforced Doping Strategy in the Multiscale PMIA Paper for High Mechanical Properties and Insulating Performance

The poly(m-phenylene isophthalamide) (PMIA) paper has attracted extensive interests due to its ultrahigh mechanical properties as an ideal protective material for anti-impact damage applications. In the pursuit of additional properties, composites based on the PMIA matrix and various fillers are widely explored. However, additional improvements are frequently obtained at the expense of mechanical properties because of the serious interfacial compatibility brought by different components. In this study, a self-reinforced doping strategy is proposed by combining microscale PMIA fibers as the fillers and nanoscale PMIA fibers as the matrix to form a micronano paper. Without the limitation of the interfacial compatibility issues, the nanofibers are tightly aligned and adhered to the microfibers, enabling the in situ generation of hydrogen bonds at the interfaces. A compact interfacial structure is thus constructed with reduced porosity on the surface. It indicates that the microfibers have a positive impact on the improvement of mechanical properties. In our optimized sample with 5 wt % microfibers, the elastic modulus, tensile strength, and elongation are 1530 MPa, 24.8 MPa, and 5.3%, respectively, which are 142, 49.4, and 65% higher than those of the pristine nano-PMIA paper. In addition, the insulating performance is also improved, facilitating its further application extended to broad fields.

Effects of UV sensitivity and accelerated photo-aging on stab resistance of ρ-aramid fabrics impregnated with shear thickening fluids (STFs)

The use of Kevlar in the field of ballistic and stabbing protection has been studied by researchers in polymeric composites for this purpose. This study presents complementary knowledge on energy absorption and dissipation in ρ-aramid fabric impregnated with shear thickening fluids (STFs), especially aiming to obtain better protection against impacts that are deeply associated with STFs, as well as color change, accelerated aging (QUV), and penetration depth (drop tower test). In addition, Scanning Electron Microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) was performed. The research shows that there was a good distribution of STF particles on the ρ-Aramid fabric surface, promoting increased friction between the interfilament and the yarns, further increasing performance and, consequently, improving the energy absorption and dissipation mechanism and, also, the penetration effectiveness in relation to non-impregnated ρ-Aramid fabric. Regarding the protection efficiency against UV exposure (250-400 nm region), there was a significantly decreased compared to those non-impregnated Kevlar® woven with STFs. The FTIR analysis showed that the conditions of aging, after exposure to UV, did not produce new functional groups, that is, there was no chemical modification. Finally, Kevlar fabric impregnated with STFs improved penetration depth performance with the blades independent of the blade type with up to 81% increase in resistance. This result was improved due to interactions between the nanoparticles present in STFs, yarns, and even high-performance woven impregnated with shear-thickening fluids.

Diagnostics of High Water Content Paper-Oil Transformer Insulation Based on the Temperature and Frequency Dependencies of the Loss Tangent

The aim of the work was to prepare and test a paper-oil insulation system according to the recommendations of CIGRE (Conseil International des Grands Réseaux Électriques) with the parameters X = 50% and Y = 30%. Pressboard was moistened to a water content of (5.0 ± 0.2) wt.% The loss tangent was measured using a DIRANA meter (FDS-PDC dielectric response analyzer) in the frequency range 10−4 Hz–5000 Hz for 6 temperatures from 293.15 K to 333.15 K with a step of 8 K. The waveforms simulated by the DIRANA software were fitted to the experimental dependence of the loss tangent. The fitting process was performed using two methods. In the first method, the measuring temperature value as well as X and Y values were entered into the software. The estimated moisture content of the insulation varied from about 1.4 to about 5.2 wt.%. The average value of moisture content was (3.73 ± 1.11) wt.%. In the second method, only the measuring temperature value was entered into the software. This improved the quality of matching. The estimated average moisture content was (5.83 ± 0.25) wt.%. It was found that the dimensions of the oil channel clearly affected the quality of the fitting process. By not taking into consideration real values of oil channel, the quality of the moisture content estimation was significantly improved.

Precise Measurements of the Temperature Influence on the Complex Permittivity of Power Transformers Moistened Paper-Oil Insulation

The reference characteristics of complex permittivity of the transformers insulation solid component were determined for use in the precise diagnostics of the power transformers insulation state. The solid component is a composite of cellulose, insulating oil and water nanoparticles. Measurements were made in the frequency range from 10−4 Hz to 5000 Hz at temperatures from 293.15 to 333.15 K. Uncertainty of temperature measurements was less than ±0.01 K. Pressboard impregnated with insulating oil with a water content of (5.0 ± 0.2) by weight moistened in a manner maximally similar to the moistening process in power transformers was investigated. It was found that there are two stages of changes in permittivity and imaginary permittivity components, occurring for low and high frequency. As the temperature increases, the frequency dependencies of the permittivity and imaginary permittivity component shifts to the higher frequency region. This phenomenon is related to the change of relaxation time with the increase in temperature. The values of relaxation time activation energies of the permittivity ΔWτε′ ≈ (0.827 ± 0.0094) eV and the imaginary permittivity component ΔWτε″ = 0.883 eV were determined. It was found that Cole-Cole charts for the first stage are asymmetric and similar to those described by the Dawidson–Cole relaxation. For stage two, the charts are arc-shaped, corresponding to the Cole-Cole relaxation. It has been established that in the moistened pressboard impregnated with insulating oil, there is an additional polarization mechanism associated with the occurrence of water in the form of nanodrops and the tunneling of electrons between them.

Influence of Oil-Pressboard Mass Ratio on the Equilibrium Characteristics of Furfural under Oil Replacement Conditions

The distribution behavior of furfural in insulation systems is influenced by the oil–pressboard mass ratio. In addition, the equilibrium distribution of furfural between oil and pressboard will be disturbed after oil replacement. Therefore, it is of great significance to study the distribution ratio of furfural in oil with various oil–pressboard mass ratios after oil replacement. In this research, an accelerated thermal aging experiment and oil replacement experiment were conducted in the lab. Furthermore, the equilibrium characteristics of furfural dissolved in oil with various oil–pressboard mass ratios were studied. Multiple regression analysis was used to analyze the relationship between the oil–pressboard mass ratios and the distribution ratio of furfural in oil. The equilibrium distribution model of furfural was thus obtained. Afterwards, the modified furfural distribution model under oil replacement conditions was established. A novel scheme is provided for analyzing the equilibrium characteristics of furfural under various oil–pressboard mass ratios after oil replacement. The work of this paper is expected to improve the accuracy of furfural analysis.

An ultra-stretchable glycerol-ionic hybrid hydrogel with reversible gelid adhesion

Functional hydrogels have attracted enormous interest as wet adhesives for biomedical research and engineering applications. However, reversible hydrogel adhesives that can be used for gelid conditions were rarely reported. In this work, we have developed a freezing-tolerant (freezing temperature < -50 °C), ultra-stretchable (stretch strain > 30000% at 25 °C) glycerol-ionic hydrogel via the ultraviolet curing of acrylamide monomer and hyper-branched polyethylenimine polymer in CaCl₂-water-glycerol solution. The fabricated hydrogel exhibited reversible gelid adhesion, rapid self-healing (recover in 3 s) and weight-retaining (>2 weeks) properties. The hydrogel allows two iron substrates to adhere together at -40 °C with the lap-shear adhesion strength as high as ~1 MPa. Such strong adhesion measured was reversible, specifically achieving ~100% of initial adhesion strength at 25 °C and ~36% at -40 °C. Additionally, decreasing the testing temperature significantly improved the tensile strength but decreased the fracture strain of the hydrogel. Interestingly, lap-shear adhesion tests suggested that the gelid adhesion strength was enhanced by 130 times as the testing temperature decreased from 25 °C to -40 °C, which was mainly attributed to the enhanced mechanical strength of the bulk hydrogel as well as the increased surface interaction at gel-substrate interfaces. More importantly, the adhesion failure gradually changed from cohesive failure to adhesive failure as the temperature decreased. This work provides new practical and fundamental insights into developing multifunctional freezing-tolerant hydrogel adhesive for gelid conditions.

Agglomeration mechanism and restraint measures of SiO2 nanoparticles in meta-aramid fibers doping modification via molecular dynamics simulations

In this work, the nanoparticle agglomeration process has been studied via molecular dynamics simulations to uncover the agglomeration mechanism. When the nanoparticles were far from each other in an aqueous solution, they mainly diffused because of influence of water molecules. When nanoparticles were close to each other, hydrogen bonds between the nanoparticles actively contributed to their agglomeration. In addition, the agglomeration of nanoparticles was also related to their sizes and concentration. A higher nanoparticle concentration led to an increased probability of nanoparticle contact and easier agglomeration. Smaller nanoparticles could diffuse quickly and aggregate more easily, hence resulting in agglomeration. Additionally, to restrain the agglomeration of silicon dioxide nanoparticles, promote compatibility between the inorganic silicon dioxide nanoparticles and organic polymer meta-aramid fibers, and strengthen the interaction between the two molecules, 3-aminopropyltriethyloxy silane was used for chemical modification of the surface of the nanoparticles. By comparing the interaction energy and hydrogen bond energy between interfaces before and after modification, a grafting density of 502% (1/Ų) was achieved, which was comparatively the best. The results of this work provide a valuable basis for further discussion and improvement of the performance of meta-aramid fiber insulation via doping hybridization with silicon dioxide nanoparticles.