Dielectric Field Research Articles

Low Thermal Conductivity Silicone Aerogels Tuned by Composite Surfactants.

The excellent flexibility of silicone aerogels has attracted attention. However, the thermal conductivity of silicone aerogels is higher than that of inorganic silicone aerogels. Thermal conductivity can be reduced by increasing the thermal insulation of silicone aerogels while maintaining their flexibility. Herein, we successfully propose an ultrasimple strategy to prepare thermally conductive silicone aerogels using composite surfactants. Cetyltrimethylammonium chloride and cetyltrimethylammonium bromide were selected as complex surfactants with effective emulsification ability. The synthesized cationic/cationic surfactant emulsion aerogels exhibited high porosity (93%), flexibility, remarkable adiabatic properties (0.021 W m-1 K-1 thermal conductivity at 25 °C), thermal stability (68.71% thermogravimetric residue at 0-800 °C), and excellent flame-retardant capacity (vertical combustion test grade = V-0; limiting oxygen index = 27.30%), which made cationic/cationic surfactant emulsion aerogels a candidate material in the field of thermal insulation.

3D printed high–strength polyimide aerogel metamaterials for sound absorption and thermal insulation

The structural manufacturing of high–performance polyimide (PI) aerogels is challenging because of the insufficient mechanical strength and rheological properties of sol–gel ink, and PI aerogels have limited application. In this study, a PI aerogel–based Helmholtz resonator (PIHM) and its acoustic metamaterial were innovatively constructed using freeze casting–assisted extrusion printing process and building block–assembly strategy, featuring a micro–perforated panel (MPP) sound–absorbing structure. The PIHM with a density of 0.294g·cm−3 achieved a compressive strength of 10.2MPa because of its periodically distributed honeycomb topology. Moreover, the PIHM not only retained the lightweight and thermal insulation characteristics of aerogels but also exhibited excellent sound–absorption performance because of the dual dissipation of sound waves by the MPP structure and PI aerogel framework. By serially connecting PIHMs with different aerogel pore sizes and leveraging the distinct acoustic properties of the layered structure along with the significant increase in relative mass resistance and acoustic impedance, the acoustic metamaterial achieved absorption coefficient peaks of 0.82–0.91 at 622–726Hz, considerably widening the bandwidth with an absorption coefficient greater than 0.8. Finally, the composite sound–absorbing panel fabricated from a PIHM combined with common building materials demonstrated strong practicability and versatility. This research has pioneered a viable method for manufacturing PI aerogels with functional structures through 3D printing, expanding their application in the field of sound absorption and thermal insulation, and paving the way for the study of aerogel metamaterials in construction.

Superior Energy-Storage Performances under a Moderate Electric Field Achieved in Antiferroelectric-like Na0.5Bi0.5TiO3-Based Relaxor Ferroelectric Ceramics by a Synergistic Optimization Strategy.

The progress of power systems and electronic devices promotes the development of lead-free dielectric energy-storage material. Particularly, Na0.5Bi0.5TiO3-based ferroelectric ceramics featuring large spontaneous polarization as well as wide dielectric adjustability and stability are highly recognized as promising candidates. However, their large remanent polarization (Pr) and low electric breakdown strength (Eb) result in unsatisfactory recoverable energy density (Wrec) and/or energy conversion efficiency (η), severely restricting their energy-storage applications. Herein, an effective synergistic optimization strategy has been proposed to gain superior energy-storage performances. Interestingly, the antiferroelectric-like (AFE-like) (1 - x)(Na0.3Bi0.38Sr0.28TiO3)-xBi(Mg0.5Zr0.5)O3 (x = 0.00, 0.05, 0.10, 0.15, and 0.20) relaxor ferroelectric (RFE) ceramics were constructed via the phase structure, the polar structure, and the defect dipole modulations. With Bi(Mg0.5Zr0.5)O3 increasing, the slim and pinched polarization-electric field hysteresis (P-E) loops become remarkably similar to the double-like P-E loops characterized by AFEs. Meanwhile, the strengthened Eb and delayed polarization saturation were also realized due to the enlarged band gap, refined grain size, and reduced free energy barrier. Consequently, superior energy-storage performances were achieved in this work. Noticeably, a large Wrec of 5.00 J/cm3 and a high η of 90.09% were realized in 0.85(Na0.3Bi0.38Sr0.28TiO3)-0.15Bi(Mg0.5Zr0.5)O3 RFE ceramics at a moderate electric field of 340 kV/cm. Additionally, excellent energy-storage and/or charge-discharge reliabilities in frequency (1-500 Hz), temperature (20-140 °C), and fatigue cycle (1-50,000) were confirmed. These satisfactory results not only indicate the promising prospects of 0.85(Na0.3Bi0.38Sr0.28TiO3)-0.15Bi(Mg0.5Zr0.5)O3 RFE ceramics in the dielectric energy-storage field but also verify the effectiveness of the synergistic optimization strategy proposed in this work.

Analysis of electric field and leakage current of glass and porcelain insulators under clean and polluted conditions: A comparative study of three profiles

Electric field (EF) enhancement in insulating systems may occur due to both internal and external factors including inefficient design, manufacturing defects, and depositions of pollutants. Consequently, phenomena like partial discharge, unexpected flashover, and even breakdown of the insulator may take place. In this work, aiming to suggest relatively better performance, a comparative study of porcelain and glass insulators under clean and polluted conditions was conducted using finite element-based software, COMSOL Multiphysics. Three profiles of both the insulators namely, standard, anti-fog, and open were modelled, and the effects of their geometry and varying electric conductivity of the surrounding air were analyzed on EF distribution and leakage current (LC). These parameters were also investigated under the deposition of water droplets and various pollution scenarios. Results of the performed computations demonstrated that by making air conductivity high, LC enhanced significantly while EF was affected the least. The presence of water droplets in the vicinity of live electrode and deposition of pollution near the end fittings created the strongest impact on EF distribution. Among the studied configurations, standard profile of porcelain material appeared to be the most promising for suppressing effects of the simulated stresses.

Tailored dielectric properties of polypropylene nanocomposites through laboratory synthesized titania

Nanofillers have drawn utmost attention for their ability to enhance the dielectric properties of polymers in the field of high voltage insulation. Usually, a small fraction of nanofillers are added to polymers, and promising dielectric property changes are resulted. Titania (TiO2) nanofiller has been widely incorporated in different polymers for dielectric properties improvements. However, the effects of rutile TiO2 and anatase TiO2 on the structure and dielectric properties of polypropylene (PP) nanocomposites have yet to be systematically compared especially from the perspective of nanodielectrics. In this study, the effects of rutile TiO2 and anatase TiO2 nanofillers on the structure and dielectric properties of PP were investigated. The rutile TiO2 and anatase TiO2 nanofillers were laboratory synthesized through a sol–gel method using two calcination temperatures, i.e., 700 °C and 450 °C, respectively. The results revealed that the rutile TiO2 and anatase TiO2 had distinct effects on the structure and dielectric properties of PP nanocomposites. Significantly, the dielectric performance of PP nanocomposites containing anatase TiO2 outperformed that containing equivalent amount of rutile TiO2. Possible mechanisms governing these changes are discussed.

Evolution laws of charge mobility of transformer oil and pressboard material with temperature and electric field strength

Abstract Charge mobility, a pivotal parameter in the space charge analysis model for oil-pressboard insulation of converter transformer under DC electric fields, predominantly relies on theoretical or empirical data. The prevalent omission of empirical, measurement-based evaluations, combined with the neglect of temperature and electric field intensity effects, introduces uncertainties in the calculation of electric field and charge dynamics. Grounded on the principles of the electroacoustic pulse technique for space charge measurements, our investigation established a temperature-controlled platform to determine the charge-charge mobility in oil and pressboard insulation mediums. Utilizing diverse oil-pressboard insulation systems, this study identified the temporal patterns of both positive and negative charge mobilities and unravelled the mechanisms modulated by temperature and electric field intensity: (1) with increasing temperatures (from 20 °C to 80 °C) and intensifying electric field strengths (from 5kV mm−1 to 25kV mm−1), the charge mobility within transformer oil and pressboard exhibits a rising trend. Notably, temperature variations exert the most significant influence, yielding amplifications up to 24.8 times. (2) The intrinsic properties of different transformer oils and oil-impregnated pressboards result in pronounced differences in their charge transport behaviors. Specifically, naphthenic-based oil demonstrates enhanced charge mobility relative to its paraffin-based counterpart. In contrast, transformer oils with higher kinematic viscosities exhibit diminished charge mobility compared to those with lower viscosities. (3) A linear relationship is observed between the oil absorption rate and electrical conductivity, aligning closely with the insulating pressboard’s charge mobility. The evaluation of electric field and interface charge dynamics in oil-pressboard insulation under both DC and polarity-reversed conditions revealed that the electric field decay in naphthenic-based oil is more rapid than in paraffin-based oils. Moreover, both the magnitude and rate of interface charge accumulation in naphthenic-based oils exceed those in paraffin-based variants, further validating the accuracy of our charge mobility measurements and ensuing analysis.

A novel colorless flexible polymer aerogel with stable amine linkage enabled superior formaldehyde removal and multifunctional application

Massive formaldehyde emissions have seriously endangered environment and human health, while predictably polymer aerogel is a promising candidate for formaldehyde (FA) removal, whereas low FA adsorption capacity, high volume shrinkage, and mechanical brittleness restrict its further development. Herein, based on “rigid-soft combination” polycondensation strategy, trifunctional 1,3,5-benzenetricarboxaldehyde (BTC) and polyetheramine Jeffamine T403 are selected as building blocks to construct a novel amine-linked polymer aerogel (rBTA) with hierarchical micro-nano porous structure via mild sol-gel method and freeze-drying process. Stable amine linkages in rBTA are formed by NaBH4 reduction of imine bonds, improving acid/alkali resistance and chemical stability greatly, and creating numerous active amine sites for reaction with FA. Formation of robust 3D covalent network facilitates to simultaneously achieve ultra-low-shrinkage (5.4%), high specific compressive modulus (5.32 kN·m·kg-1), remarkable mechanical durability/fatigue-resistance, flexibility, and machinability. Benefiting from synergistic physical-chemical adsorption effect, FA adsorption capacity and removal ratio of rBTA reach as high as 459.84 mg·g-1 and 97.87%, respectively. Colorless rBTA is further ground into powders for preparing polyoxymethylene (POM)/rBTA composite without affecting its color and formaldehyde emission amount at 60/230°C effectively decreases by 66.87%/79.55%. Furthermore, rBTA exhibits hydrophobicity, low thermal conductivity, and high solar reflectance, being successfully applied in emulsion separation, thermal insulation, and energy-efficient buildings fields.

The synergistic sintering of ultra-lightweight ceramsite from molybdenum ore tailings, iron ore tailings and waste glass powders: Properties and formation mechanism

Molybdenum ore tailings, iron ore tailings and waste glass powders are important industrial solid wastes, mainly composed of silicate minerals and quartz, which are expected to become alternative resources for inorganic non-metal industrial materials. In this paper, the ultra-lightweight ceramsite was prepared by the synergistic sintering of molybdenum ore tailings, iron ore tailings and waste glass powders according to their characteristics of silicate minerals. The physical and mechanical properties were investigated when the sintering temperature was between 1100 and 1140 °C. The evolution of mineral phases and formation mechanism of pore structure during sintering were studied by XRD, FT-IR, SEM, TG-DSC and HSM. The results showed that in the sintering process, the waste glass powders and the pargasite in iron ore tailings first melted to produce the initial liquid phases. Then the anorthoclase and the quartz in molybdenum ore tailings melted to produce a large amount of liquid phases. These liquid phases covered the gas generated by the oxidation of SiC, thus forming a rich pore structure. At the same time, the [Si2O64−] and Ca2+, Mg2+ in the liquid phases derived from quartz and pargasite melting recrystallized to form diopside, which was conducive to the improvement of mechanical properties of ceramsite. When the raw material ratio of molybdenum ore tailings, iron ore tailings and waste glass powders was 6:2:2 and the sintering temperature was 1120 °C, the pore structure of the ceramsite as prepared was uniform and rich and mostly closed. The density was low and the mechanical propertities were excellent. It has a good application prospect in the field of building thermal insulation and sound insulation.

Polyetherimide copolymer film with room-temperature self-healing properties and high breakdown field strength

With the waste of resources caused by human activities, it has gradually become an increasingly prominent social problem. The development of self-healing polymers in the field of insulation has attracted widespread attention. Develop polymer matrices with efficient healing efficiency and sound insulation properties to achieve green and sustainable resource conservation. In addition, improving the dielectric properties of intrinsic self-healing matrices has been a hot topic. In this work, we developed a new PEI matrix-modified self-healing polymer substrate that provides a breakdown field strength of 240 kV/mm and self-healing properties at room temperature, this has significantly improved the dielectric properties over other previously reported self-healing polymers. In addition to the abovementioned performance, we found significant differences in thermodynamic behavior in the synthesized end-modified polymers. By dielectric characterization (LCR), the breakdown composite can be left at room temperature for 60 min, and the material can recover 80 % of the initial properties without external intervention(This is demonstrated by the fact that its DC conductivity at 60 min of autonomous healing was significantly changed from that of the freshly electrically pierced DC conductivity and remained around 5.38 × 10−11 S/cm for a longer period of time thereafter). The microscopic morphology of the modified PEI matrix was observed by scanning electron microscopy (SEM) and EDS surface elemental analysis, which further supports the existence of metal coordination structures. These findings can further deepen the thinking of self-healing dielectric composites. The work inspired by this may break the limits and take self-healing composite dielectric materials to a new height.

Effect of different silane coupling agent modified SiO2 on the properties of silicone rubber composites: Based on molecular dynamics

Silicone rubber composites doped with nanoparticles are widely used in the field of electrical and aerospace insulation. The silane coupling agent modified on the surface of the particles enhances the compatibility between the nanoparticles and the insulating material, thus further improving the mechanical, dielectric properties and thermal stability of the composites. On this basis, the silicone rubber composite system models of three silane coupling agents (KH550, KH560, KH570) modified SiO2 are established respectively. Through the analysis methods of interaction energy, free fraction volume, radial distribution function and pull-out simulation, the improving mechanism of three silane coupling agents modified SiO2 on material properties can be explored from the perspective of molecular simulation. The results show that the interaction energy between KH570/SiO2 and silicone rubber system is the largest regardless of temperatures (280 K ∼ 400 K). At low temperature (280 K), the free fraction volume of KH550 and KH560 modified SiO2 systems is lower than that of KH570 modified system, while at high temperature, the free fraction volume of KH570/SiO2 system is the lowest. The three silane coupling agents modified SiO2 all increase the Young's modulus and bulk modulus of silicone rubber composites, and reduced the relative dielectric constant of the composites. The silicone rubber composite system mixed with KH570/SiO2 has the largest adsorption capacity for water molecules and the most obvious effect to inhibit the diffusion of water molecule. The results of this work can provide reference for the design and performance optimization of modified SiO2/silicone rubber composites in hygrothermal environment.

Enhanced energy storage performance in NBT-based MLCCs via cooperative optimization of polarization and grain alignment

Dielectric ceramics possess a unique competitive advantage in electronic systems due to their high-power density and excellent reliability. Na1/2Bi1/2TiO3-based ceramics, one type of extensively studied energy storage dielectric, however, often experience A-site element volatilization and Ti4+ reduction during high-temperature sintering. These issues may result in increased energy loss, reduced polarization and low dielectric breakdown electric field, ultimately making it challenging to achieve both high energy storage density and efficiency. To address these issues, we introduce a synergistic optimization strategy that combine polarization engineering and grain alignment engineering. First principles calculations and experimental analyses show that the doping of Mn2+ can suppress the reduction of Ti4+ in Na1/2Bi1/2TiO3-based ceramics and enhance ion off-centering displacements, thereby reducing energy loss and improving polarization. In addition, we prepared multilayer ceramic capacitors with grains oriented along the <111> direction using the template grain growth method. This approach effectively reduces electric-field-induced strain by 37% and markedly enhances breakdown electric field by 42% when compared with nontextured counterpart. As a result of this comprehensive strategy, <111 >-textured Na1/2Bi1/2TiO3-based multilayer ceramic capacitors achieve an ultra-high energy density of 15.7 J·cm−3 and an excellent efficiency beyond 95% at 850 kV·cm−1, exhibiting a superior overall energy storage performance.

Enhancing insulating properties of glass-fiber reinforced polymers using plasma fluorination-modified boron nitride nanosheets

The insulation failure of glass fiber-reinforced polymers (GFRP) limits their use in high-voltage insulation fields. In this study, boron nitride nanosheets (BNNS) were prepared using ball-milling and further fluorinated via dielectric barrier discharge (DBD) plasma treatment. The GFRP nanocomposites were fabricated using different filler types and doping concentrations. The test results indicated that fluorinated BNNS (F-BNNS) displays good dispersion and interfacial compatibility, enhances the interfacial bonding strength of the “fiber-matrix-filler” ternary system in GFRP, and reduces the internal defects of materials. In addition, the insulating properties of the composites were related to the filler concentration. Adding a trace amount of F-BNNSs increased the flashover and breakdown voltages of the GFRP by up to 28.77% and 21.62%, respectively. The results of molecular dynamics simulations and trap distribution calculations showed that plasma fluorination of BNNS increases the bandgap and deep trap energy level at the interface. The extremely strong charge-binding ability of the deep traps inhibits continuous charge injection and regulates carrier migration, which improves the insulating properties of the composites. The results of this study provide a novel, environmentally friendly, and efficient solution for improving the insulating properties of GFRP.

Synergistically Constructing High-Dielectric Poly(m-phenylene isophthalamide)/Silica/Cellulose Nanofiber Composite Insulation Paper through Dynamic Covalent Chemistry and Hydrogen Bonding.

The rapid advancement of modern power equipment and high-power devices has imposed increasingly stringent demands upon the mechanical and dielectric properties of electrical insulation materials. Herein, we report a poly(m-phenylene isophthalamide) (PMIA) composite insulating paper with excellent dielectric breakdown strength, reliable mechanical properties, and high thermal stability. Enhanced surface activity of PMIA is achieved through surface modification, facilitating the synergistic integration of modified PMIA (MPMIA), bovine serum albumin (BSA)/silica (SiO2), and cellulose nanofiber (CNF) into composite paper using dynamic covalent bonds and hydrogen bonding. The prepared MPMIA-BSA/SiO2-CNF composite paper exhibits a laminated stacked structure with high tensile strength (32.68 MPa) and strain at break (9.57%). Meanwhile, MPMIA-BSA/SiO2-CNF composites have excellent dielectric breakdown strength (24.75 kV/mm) and good temperature resistance. Therefore, the MPMIA-BSA/SiO2-CNF composite paper has a broad application prospect in the field of high-voltage and high-power electrical equipment insulation.

Comparing low frequency impact insulation measured with the rubber ball versus the tapping machine

The heavy/soft impact source or rubber ball, defined in ISO 10140 and 16283, is used primarily in Japan and Korea to evaluate low-frequency impact insulation from sources such as walking without shoes and children jumping. ASTM test methods currently do not include the heavy/soft source, and low frequency impact noise insulation is currently measured with the tapping machine using ratings such as LIR and LIIC per ASTM E3207. ISO ratings using spectrum adaptation terms from 50 Hz or lower can also be used. The relationship between these ratings and those measured using the heavy/soft source has not been well characterized for assemblies that are common in North America. The authors present field and laboratory data of impact insulation with both sources. Analysis of the data describes the relationship between the sources, the information they provide to the designers of floor assemblies, and implications for classifications of low frequency impact insulation.

Online control of educational results of the unit “Electricity” in the conditions of blended learning

Abstract The article describes the technology of online control of educational results of the unit “Electricity” in the conditions of blended learning. It was determined that during the online stages of studying unit “Electricity”, reverse communication is an urgent issue when receiving information in a distance format, and online control is designed to support the organization of a modern training session. Three topics have been singled out in the unit, in the context of which it is appropriate to develop control measures. Topic I “Electric Field in a Vacuum” focuses on the study of electric field strength, potential, the relationship between strength and potential, the electric dipole, and the circulation and flow of an electric field. Topic II “Electric Field in a Substance” involves the study of the electric field in dielectrics and conductors in an electric field. Topic III “Electric Current” includes general laws of electric current, electric circuit, current in a circuit with a capacitor, and current work and power. There are outlined the different types of tests: graphical, calculation, animated, audio that form the means of online control in the context of the outlined unit. The developed technology of online control of educational results of the unit “Electricity” provides for an organic combination of the presentation of educational materials with control measures. The research methodology involved the analysis and synthesis of scientific, pedagogical, methodological sources and empirical methods, as well as the analysis of the obtained results. Before the introduction of the developed technology and after the completion of the experimental work, a study was conducted, which included an analysis of the quality of knowledge when studying the specified topic. The obtained results before and after the experiment were tested using the Pearson statistical test χ 2.

Cellulose nanofibers enabled strong and flexible plant-derived thermoplastic polyester elastomer foams for high-performance thermally insulating applications

Flexible thermal insulation materials have garnered significant attention owing to the proliferation of flexible electronic devices and their diverse application environments. Plant-derived thermoplastic polyester elastomer (TPEE) foams emerge as promising candidates in the field of flexible thermal insulation. However, inevitable shrinkage behavior of TPEE foams would result in reduced porosity and inferior thermal insulation performance. Hence, a pioneering approach is proposed wherein cellulose nanofibers (CNF) are integrated into TPEE matrixes, complemented by microcellular foaming, aimed at mitigating shrinkage process and enhancing thermal insulation properties. In this work, the relaxation behavior of nanocomposite, corresponding to shrinkage process, has been elucidated through dynamic mechanical analysis. It's found that entanglement of CNF could heighten the internal friction with TPEE molecular chains, coupled with establishment of hydrogen bonds, thereby curbing relaxation phenomena and facilitating the attainment of foams with enhanced and stable porosity. The shrinkage ratio of TPEE/CNF composite foam could be reduced by 20 % without compromising the final porosity. The thermal conductivity would decrease to 37.9 mW/m·K for the TPEE/CNF composite foam with the higher porosity of 0.947. Moreover, the utilization of CNF presents a novel avenue for fabricating TPEE/CNF nanocomposite foams endowed with flexibility, lightweightness, increased porosity, and reduced thermal conductivity.

Superhydrophobic nanocellulose aerogel for thermal insulation and thermal resistance up to 1300 °C

Nanoellulose aerogel (NCA) has the advantages of good flexibility, low density, and excellent thermal insulation. Its raw materials are widely sourced, renewable, and degraded, thus NCA has attracted significant interest ofresearchers in the field of insulation. However, low strength, hydrophilicity, and flammability seriously hinder its application. Here, a superhydrophobic NCA (Si-PA-PAE-NCA) with a multiscale structure is reported. Si-PA-PAE-NCA exhibits excellent compression strain (up to 8.674 MPa with strain at 80 %). A low thermal conductivity of 23.9 mWm−1 K−1 endows this aerogel with superior thermal insulation property. Compared to only the surface superhydrophobility of other NCAs, both the surface and interior water contact angles of Si-PA-PAE-NCA are up to 157°. Owing to this distinguished superhydrophobicity, Si-PA-PAE-NCA can maintain its stable thermal insulation property in a high humidity environment (90 % humidity). Importantly, Si-PA-PAE-NCA can withstand 1300 ℃ flame for 70 min, far exceeding previously reported NCAs. Besides, this aerogel exhibits the highest LOI value (45.9 %) ever recorded for NCAs thus far. Notably, there is no inorganic substance within the aerogel. Together with its scalability, sustainability, and degradability, Si-PA-PAE-NCA will have great application prospects in the insulation area.

The impact of XLPE surface defects on electric field and breakdown voltage

During the construction of cable joints, three common defects may occur on the XLPE surface: scratches, moisture exposure, and adhered contaminated particles. To evaluate the impact of these defects on joint performance, this paper establishes a sheet model of XLPE insulation in cable joints to analyze the changes in the electric field under different defects and explore the influence of different defects on the electric field and breakdown voltage. Results of the study reveal that the electric field at the scratch site on XLPE produces severe distortion, being 1.6 times that of non-scratch areas. When exposed to moisture, the more conductive impurities present in the adhered contaminated water on the XLPE surface, the higher the conductivity of the contaminated water, thereby increasing its conductive performance and the electric field strength, which is 1.22–1.4 times that of the non-moist interface. When particles adhere to the XLPE surface, severe distortion occurs at the particle-interface electric field, approximately 1.5 times that of the defect-free interface. Scratches have the most significant impact on the electric field of XLPE insulation. Experimental results also demonstrate that the breakdown voltage without defects is 129.6 kV, while the breakdown voltage with scratch defects is 59.1 kV, moisture defects is 69.7 kV, and particle contamination defects is 59.2 kV, with scratches having the most significant impact on the breakdown voltage of XLPE insulation. These findings provide important insights into the influence of different defects on the insulation performance of cable joints.

Thermal, mechanical property and flame retardant analysis of bio-based rigid polyurethane foam modified with expandable graphite

As an energy-efficient building material, rigid polyurethane foam (RPUF) has attracted attention. However, there are still great challenges in how to easily prepare RPUF materials with good mechanical properties, flame retardant properties, thermal insulation and other properties. In the current work, expandable graphite (EG)-modified lignin-based polyol (RPUF) was prepared by a one-step method. Thermogravimetric analysis was used to study the pyrolysis of modified foams under nitrogen conditions. It was found that the RPUF-4 with an EG of 10 wt% had the highest the apparent activation energy (E), integral procedural decomposition temperature (IPDT), initial temperature and residue rate. And RPUF-4 also had excellent thermal insulation properties. In addition, RPUF-4 exhibited excellent flame retardancy and smoke suppression properties (peak heat release rate (RHRR), total heat release rate (THR) and Ds were 65.46 %, 23.92 % and 45.94 % lower than those of the unadded RPUF, respectively). At the same time, RPUF-4 also had good mechanical properties and energy absorption properties. These results will lay the foundation for the development and application of RPUF in the field of building insulation.

Investigation of fibre-modified silica aerogel composites

Abstract This investigation evaluates the thermal and mechanical performance of fibre-reinforced silica aerogel composites by introducing an optimised fabrication process and vacuumization. The novelty of this investigation was the identification of the minimum amount of solvent being used to synthesise aerogel, as well as the introduction of temperature ageing (45 °C). These provide a valuable guide for lowering the fabricating cost with optimised properties of aerogel composites. The glass fibre (GF)–aerogel composites obtained from the optimised process showed excellent thermal conductivity (18.4 mW m−1 K−1 at a pressure load of 2 psi (13.8 kPa)). It is worth mentioning that vacuum sealing of the aerogel composites not only prevents dustiness during handling but also improves the thermal performance. The thermal conductivity could be further reduced to 13.8 mW m−1 K−1 by vacuum sealing the GF–aerogel composite. The compression and bending tests proved that the aerogel composites could endure considerable compressive and flexural strain without structural destruction. These outstanding characteristics indicate that GF–aerogel composites have great potential in the thermal insulation field, especially for a moderate temperature environment (i.e., less than 800 °C).