Excellent Heat Insulation Research Articles

Fabrication and Properties of Nanometer Multilayer Compound Heat Insulation Material

This research focuses on the development of a nanometer multiple-layer compoundheat insulation material and its preparation procedure. The material consists of alternating layers of an infrared reflecting screen and a spacer. The infrared reflecting screen is made of metal foil or metal plated foil, while the spacer is a thermostability nanometer porous aerogel compoundheat insulation material. The layers are combined using thermostability adhesives or puncturing connection with thermostability sewing threads. The objective of this study is to investigate the properties and preparation procedure of the nanometer multiple-layer compoundheat insulation material. The material offers low density, favorable mechanical properties, and excellent high-temperature heat insulation performance. It reduces the vacuum requirements for vacuum insulation plate core materials and eliminates the need for getters. This material meets the high-efficiency heat insulation requirements of aviation, aerospace, and civil applications. Moreover, the proposed procedure enables the production of large-sized heat insulation material members with complex shapes.

Synthesis of a novel multifunctional montmorillonite/L-malic-acid/curcumin/bacterial cellulose hybrid nanofilm with excellent heat insulation, antibacterial activity and cytocompatibility

Synthesis of a novel multifunctional montmorillonite/L-malic-acid/curcumin/bacterial cellulose hybrid nanofilm with excellent heat insulation, antibacterial activity and cytocompatibility

Strut effectiveness factor and maximum shear strength of Infra Lightweight Concrete (ILC)

Infra Lightweight Concrete (ILC) is a versatile construction material that is characterized by its substantial lightweight (dry density ≤ 800 kg/m3), an excellent heat insulation and a sufficient bearing strength. Given these properties, ILC has been presented as a promising approach for modern building envelops, offering a viable alternative to conventional building façades. This implies that composite exterior walls combining a bearing element and several insulating layers can be efficiently replaced by a single ILC layer. This replacement offers several advantages related to building sustainability and allows architectural innovation. The first realistic mix and the first ILC building date back to less than two decades. Since that time, ILC has built a solid reputation among ecologically aware designers. Therefore, many successful mixes were developed, resulting in a significant improvement of its mechanical properties. Also, several studies have been conducted to understand its structural behaviour, including studies on its bond, compressive, flexural and, most recently, shear behaviour. One of the key challenges revealed by these studies is the ILC high brittleness and moderate strength, both hindering in most cases the full development of reinforcement strength, thereby, limiting the capacity of reinforced ILC sections. This work experimentally handles the shear strength limit of ILC beams with web stirrups. This limitation was frequently set to preclude the compressive failure of inclined struts prior to the development of web stirrups capacity. Five ILC beams made of five ILC mixes were tested in a 4-point bending test, with beams configuration and test setups were adapted to push the failure to the crushing of inclined struts by excessive compression. The equalization of experimental to theoretical strength of inclined strut assisted in obtaining the ILC’ strut effectiveness factor (βs = 0.83). The maximum shear strength was, then, linked to the strut capacity that is directly related to the ILC strength and the estimated βs.

Facile construction of organic–inorganic hybrid flame-retardant system based on fully biomass: Improving the fire safety and mechanical property of epoxy resin

As the contradiction intensifies both the increasing consumption of petroleum resources and environmental protection, the exploitation and utilization of biological resources have reached an unprecedented height. Hence, an organic–inorganic hybrid system, called ammonia phytate modified oyster waste nanosheets (TOSP@PAA), was constructed via mechanochemical strategies and used for flame-retardant EP. The characterization revealed that TOSP@PAA showed a specific layer crosslinking structure by the NH3+OP bond. The calcination experiment revealed that TOSP@PAA possessed excellent self-charring performance and formed a highly intumescent char residue layer at high temperatures. In addition, the combustion tests indicated that EP with TOSP@PAA showed noticeable fire safety (e.g., ∼74.0 % and 60.2 % decline in peak heat release rate (pHRR) and total heat release rate (THR) at only 8 wt% content) and excellent heat insulation properties. Remarkably, EP with TOSP@PAA exhibited good mechanical properties with remarkable improvement in flexural properties. The work provides new sights on the facile preparation of environmentally friendly flame retardants and explores a new way to strengthen the fire safety and mechanical property of EP.

Electric field regulation of polypropylene insulation for high voltage DC cables

High voltage cable is the key factor to determine the quality and capacity of power transmission. Polypropylene has widely attracted more attention because of its excellent heat resistance, insulation and green environmental protection, and it is used as cable material. Polypropylene insulation material for high voltage cable needs to bear pulsed voltage and the DC rated voltage, which can easily cause electric field to be distorted and lead the space charge to be accumulated. Meanwhile, the change of cable temperature will also affect the conductivity of insulating material and promote the accumulation of space charge, resulting in the distortion of internal electric field of insulating material and the initiation and growth of electric tree. Therefore, it is necessary to regulate the electric field of high voltage cable so as to suppress the deterioration phenomena such as electric field distortion, partial discharge and electrical demoralization. In this work, the theory and method of regulating DC electric field of polypropylene insulation of high voltage cable is first introduced. Then the main direction of electric field regulation is presented. Finally, the application prospect of polypropylene cable insulation is also put forward.

Enhanced flame resistance of cellulose aerogel by ammonium polyphosphate for heat insulation

Cellulose aerogels are a potential candidate for heat insulation, but one of their drawbacks is high flammability hindering their applications in practice. This study synthesized cellulose aerogels from microfibrillated cellulose fibers (MFC) extracted from discarded pineapple leaves. The procedure started with simply mixing the extracted fibers with polyamide amine-epichlorohydrin (PAE) as a chemical crosslinker and ammonium polyphosphate (APP) (10-20%) as a green and effectively flame-resistant additive, followed by freeze-drying. The produced aerogels are characterized in terms of their morphology, thermal stability and conductivity, and flame resistance via advanced and standardized methodologies including Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), thermal conductivity measurement by a heat flow meter, and UL94 horizontal burning test. The flame-resistant cellulose aerogels exhibit ultra-low density (25.5-26.8 mg/cm3), high porosity (98.0-98.2%), excellent heat insulation (35.9-36.7 mW/m۰K), and are completely flame-resistant. In addition, the varied APP content (10-20%) shows little effect on the density, heat conductivity, and thermal stability of the flame-resistant cellulose aerogels in comparison with that of the neat cellulose aerogel. Based on the findings, the synthesized flame-resistant cellulose aerogels are considered a promising bio-based heat insulation material.

Fabrication of Robust Waterborne Superamphiphobic Coatings with Antifouling, Heat Insulation, and Anticorrosion.

Water-based superamphiphobic coatings that are environmentally friendly have attracted tremendous attention recently, but their performances are severely limited by dispersibility and mechanical durability. Herein, a dispersion of poly(tetrafluoroethylene)/SiO2@cetyltrimethoxysilane&sodium silicate-modified aluminum tripolyphosphate (PTFE/SiO2@CTMS&Na2SiO3-ATP) superamphiphobic coatings was formed by mechanical dispersion of poly(tetrafluoroethylene) emulsion (PTFE), modified silica emulsion (SiO2@CTMS), sodium silicate (Na2SiO3), and modified aluminum tripolyphosphate (modified ATP). The four kinds of emulsions were mixed together to effectively solve the dispersity of waterborne superamphiphobic coatings. Robust waterborne superamphiphobic coatings were successfully obtained by one-step spraying and curing at 310 °C for 15 min, showing strong adhesive ability (grade 1 according to the GB/T9286), high hardness (6H), superior antifouling performance, excellent impact resistance, high-temperature resistance (<415 °C), anticorrosion (immersion of strong acid and alkali for 120 h), and heat insulation. Remarkably, the prepared coating surface showed superior wear resistance, which can undergo more than 140 abrasion cycles. Moreover, the composite coating with 35.53 wt % SiO2@CTMS possesses superamphiphobic properties, with contact angles of 160 and 156° toward water and glycerol, respectively. The preparation method of superamphiphobic coatings may be expected to present a strategy for the preparation of multifunctional waterborne superamphiphobic coatings with excellent properties and a simple method.

A 3D multifunctional nitrogen-doped RGO-based aerogel with silver nanowires assisted self-supporting networks for enhanced electromagnetic wave absorption

We designed a promising three-dimensional (3D) nitrogen-doped reduced graphene oxide-based aerogel (NGA) with silver nanowires (Ag NWs) assisted self-supporting networks for enhanced electromagnetic wave (EMW) absorption. 3D AgNWs@NGAs (8–12 mg/mL) were synthesized by a three-step strategy of sonication, reduction, and lyophilization. The results show that introduced sp3 defects and disordered sites in nitrogen doping from a rarely-reported liquid nitrogen source of acetonitrile remarkably improved electronic dipole polarization relaxation and EMW absorption ability. Besides, electronic band structure and density of states of the NGA were investigated by first-principles calculations to indicate that the carrier mobility became smaller during nitrogen doping. The Ag NWs were distributed on an NGA as the 3D network structure of an elastic support and a conductive and compatible unit, which limited the aggregation of NGA flakes, and further strengthened conductive loss. Significantly, the synthesized ultralight AgNWs@NGA exhibits excellent performance at 9.52 GHz, with a strong minimal reflection loss of –79.99 dB, a small thickness of 2.660 mm, a wide effective absorption bandwidth of 3.5 GHz, and an ultra-low filler content of 5 wt%. Furthermore, a large specific surface of 331.5 cm3/g, a good conductivity of approximately 50 S/cm, a high resilience, and an excellent heat insulation capability, guarantee the durable stability in EMW absorption of AgNWs@NGAs to resist distortion and heat attacks.

Multifunctional MXene-based fire alarm wallpaper with sandwich-like structure for enhanced fire safety and prevention

Design and development of multifunctional fire-resistant and fire alarm wallpaper (FAW) that can simultaneously hold early fire warning function and the ability to inhibit flame propagation is urgently required to boost the fire safety of combustible materials in public security. Herein, a flexible sandwich-like and nacre-biomimetic FAW was fabricated by using renewable lignocellulose nanofibrils (LCNF) and MXene thermosensitive sensor via a vacuum-assisted alternate self-assembly method. The FAW achieved ultrasensitive fire early warning response because of the synergistic effect of the insulating LCNF layers and highly conductive MXene with hierarchical structure sandwiched between LCNF layers. Furthermore, owing to the ultrafast catalytic char formation and intumescent flame retardant effect of ammonium polyphosphate (APP), the trigger sensitivity and thermal oxidation capacity of the FAW (LCNF-15) were greatly optimized by adding 15 % APP in the LCNF layer, resulting in a superior fire alarm response (0.32 s) and a continuous alarm signal (about 3073.0 s) under a flame attack. Besides, the LCNF-15 also exhibited good flexibility, ideal cyclic warning performance, excellent heat insulation ability and strong char-forming properties in a fire. The sandwich-like strategy offers a new platform for the construction of MXene-based multifunctional FAW, which is of great value in broadly addressing the fire hazard problem of traditional wallpapers.

Nanostructured multifunctional wood hybrids fabricated via in situ mineralization of zinc borate in hierarchical wood structures

Developing feasible and eco-friendly methods to fabricate multifunctional wood remains an imperative yet challenging task. Prompted by biomineralization, this study proposes the fabrication of nanostructured wood hybrids with efficient flame retardancy, smoke suppression, mold resistance, and antitermite activity via in situ mineralization of nanosized zinc borate (ZnB) particles in a hierarchical void system of wood. ZnB was successfully deposited in the hierarchical nano/microporous cell wall structures, as confirmed by X-ray microtomography and energy-dispersive X-ray spectroscopy. The mineralized wood exhibited excellent heat insulation performance during combustion. The limiting oxygen index of the mineralized wood with 22.1 wt% ZnB (MW22) increased from 22.6% of the untreated wood to 41.2%. Cone calorimetry testing revealed reductions of 51.4%, 89.0%, and 79.5% in average CO yields, total smoke production, and maximum smoke production ratio, respectively, in MW22 relative to those in the untreated wood; the peak heat release rate and total heat release also decreased by 46.9% and 47.9%, respectively. A noncombustible film of molten ZnB covered and cross-linked the carbonaceous char layer, forming a cohesive and robust 3D residual skeleton, which endowed thermal insulation to the wood, delayed oxygen diffusion, reduced flammable gas release, and suppressed toxic smoke. Antitermite tests showed a mothproofing rating of 10 for MW22, far higher than the rating of 4 for untreated wood. Moreover, MW22 exhibited exceptional mold resistance, with an average infection of 0 and an average protective efficiency of 100%. Therefore, in situ mineralization of the wood cell wall architecture with ZnB provides a facile and feasible strategy to fabricate multifunctional integrated wood, which is suitable for scaling up and can be potentially used in modern green buildings.

Multi-Objective Design for Critical Supporting Parameters of Vacuum-Insulated Glazing with a Case Study

Vacuum-insulated glazing (VIG) has excellent sound and heat insulation and anti-fogging properties, having been a typical structure–function-integrated glass deep processing product. However, overlapping, vacancy and excessive spacing distance of the supporting pillars will increase the concentrated stress for the glass substrate, raising the potential risk of failure. Therefore, this study, aiming to address the high cost of sample preparation and the multiple factors affecting stress distribution, developed a multi-objective design for supporting stress. In this paper, a multi-objective optimization model was designed based on comprehensive mechanical analysis under square-distributed supporting. The critical supporting pillars radius as well as the critical spacing distance were solved and met the strength requirement. Case simulation demonstrated that a 0.2 mm or more radius and a 63 mm or less spacing distance for the supporting pillars were acceptable placement methods which conformed to the design requirements. This research will act as a theoretical reference for future studies, promoting the in-depth development of VIG and exploration of high-strength safety products.

Ultralight and hydrophobic PVDF/PMMA open-cell foams with outstanding heat-insulation and oil-adsorption performances fabricated by CO2 molten foaming

Heat-insulation and oil-water separation are critical issues in the area of energy conservation and environmental protection. Developing high-expansion open-cell polymer foams with excellent heat insulation and oil-absorption properties is an essential way to solve the above problems. An innovative method for fabricating lightweight PVDF open-cell foam via blending with PMMA followed by a supercritical carbon dioxide molten foaming process was proposed, and ultralight and hydrophobic polymer open-cell foams with outstanding heat insulation and oil-absorption properties were successfully prepared. PMMA not only delays cooling crystallization behavior of PVDF but also improves the melt viscoelasticity. As a result, the open-cell polymer foam with an expansion ratio of up to 43.2, open porosity of 98.6 %, and a density of 0.0361 g/cm3 can be obtained. Benefiting from high expansion ratio and high open porosity, the blend foam displays a thermal conductivity of 31.07 mW∙m−1∙K−1, an adsorption capacity for various oils as high as 8.1–23.1 g/g, and favorable cycle durability. This work provides a green and sustainable method for mass production of better-behaved foam materials for heat insulation and oil-water separation.

A dual-band transceiver with excellent heat insulation property for microwave absorption and low infrared emissivity compatibility

Electromagnetic wave absorbers with low infrared emissivity and excellent thermal insulation properties are attractive for multi-spectrum bands compatibility applications, but simultaneously meeting these requirements remains a great challenge. In this work, reduced graphene oxide/copper sulfide/stearic acid (rGO/CuS@SA) aerogels loaded with phase change materials were prepared by facile solvothermal and freeze-drying technique. Due to the existence of CuS nanoparticles, the multiple reflection and scattering of incident electromagnetic waves are enhanced, so the microwave absorption performance is improved. As a result, the reflection loss (RL) of the sample reach −52.4 dB with an effective absorption bandwidth of 5.75 GHz at 2 mm. It has certain infrared stealth function at critical moment, compared with rGO, the infrared emissivity decreased from 0.89 to 0.59. And the phase change material (stearic acid) has a large latent heat of phase change, which is available to improve the thermal insulation performance of the material. When the detection angle θ is 0°, the maximum radar cross-section (RCS) reduction value of the sample reaches 23.85 dB m2. This work provides directions for designing light-weight absorbers with low infrared emissivity and thermal insulation performance for dual-spectrum bands compatibility.

Thermal Insulation and Moisture Resistance of High‐Performance Silicon Aerogel Composite Foam Ceramic and Foam Glass

With the globalization of green energy‐saving buildings, improving the thermal insulation performance of building exterior walls has become an important breakthrough in reducing building energy consumption. And the building envelope to improve insulation properties as a starting point for energy saving. Herein, a new type of material with excellent heat insulation and moisture resistance is developed. Hence, the sol–gel process, high‐pressure impregnation as well as supercritical drying are used to synthesize foam ceramic composite SiO2 aerogel (FC@SA) and foam glass composite SiO2 aerogel (FG@SA) materials. While maintaining the porous nanostructure of the aerogel, the aerogel is filled and embedded in the pores of the foamed material by a high‐pressure impregnation method. The thermal conductivity of FC@SA and FG@SA are, respectively, 0.04159 and 0.04424 W (m K)−1 at 25 °C, which are 36.02% and 23.72% lower than foam ceramic and foam glass. FC@SA reached water saturation (49%) in 48 h, while it took 72 h for FG@SA to reach water saturation (38%). Therefore, the composite building material prepared by embedding nano‐aerogel into ceramic foam and foam glass has great potential in the insulation material of building fence structures.

Ni Flower/MXene-Melamine Foam Derived 3D Magnetic/Conductive Networks for Ultra-Efficient Microwave Absorption and Infrared Stealth

HighlightsNi-MXene/MF foam is synthesized via an electrostatic assembly and dip-coating process.The “micro-capacitor” structure of Ni/MXene and the 3D porous structure of MF endow the foam excellent impedance matching and wave absorption performance.The excellent heat insulation, infrared stealth, and flame-retardant performances are achieved.

An efficient approach to fabricate lightweight polyimide/aramid sponge with excellent heat insulation and sound absorption performance

Polyimide sponges have bright prospects in the weight reduction, heat insulation, and sound absorption equipment of aerospace, navigation, and other area due to their unique three-dimensional cellular structure and outstanding comprehensive performance. However, most polyimide sponges suffered from long and complex fabrication processes. Herein, an efficient and scalable approach, i.e. water-based foam forming, was proposed to fabricate ultralight and porous polyimide/aramid sponges (PASG). Attributed to the bubble-template nature of foam-forming, PASGs exhibit high porosity (>99%) and ultra-low density (∼10 mg/cm3), and possess excellent thermal and sound insulation performance with an optimum thermal conductivity of 34.89 mW/m·K and noise reduction coefficient of 0.41. Besides, PASGs demonstrate outstanding mechanical properties after 500 compression cycles. This strategy providing more possibilities for developing the next generation of high-performance thermal insulation and noise reduction materials.

Controllable synthesis of a robust sucrose-derived bio-carbon foam with 3D hierarchical porous structure for thermal insulation, flame retardancy and oil absorption

The fast exhaustion of the fossil fuels has led to an imperious need for more energy-efficient and environmentally friendly strategies to develop the carbon materials with high structural efficiency and multi-functional integration. Sucrose represents a promising biomass source for obtaining the carbon foams. However, the uncontrolled foaming restricts the preparation and performance of the efficient sucrose-based carbon foams. Herein, a novel route of template-free mechanical foaming-gel has been reported to fabricate the robust and multifunctional sucrose-derived carbon foams with the hierarchical porous structure. The pore structure and porosity could be flexibly controlled by tuning the sucrose concentration during the mechanical stirring process. The synergy between sucrose and epoxy hydrogel as a network skeleton endowed the carbon foams with a high carbon yield (44.7%) and optimal specific mechanical properties. The carbon foams after heat treatment at 1200 °C displayed a low density (0.089–0.195 g/cm3) and a high compression strength (1.02–4.93 MPa). The foams also exhibited excellent heat insulation performance and flame retardancy. The thermal conductivity of the carbon foam with a density of 0.089 g/cm3 was as low as 0.092 W/m·K at room temperature and 0.269 W/m·K at 1200 °C under argon atmosphere. Furthermore, the carbon foams revealed a high oil absorption capacity, together with an optimal recyclability on combustion. Meanwhile, the foams also maintained superhydrophobicity after immersion in acidic, alkaline and salty media for 120 days. The developed strategy could not only realize the preparation of the energy-efficient and environmentally-friendly bio-carbon foams with a reliable self-adaptability to the extreme environments, but also exhibited promising universality and flexibility in designing the carbon materials for applications in aerospace and oil spill cleanup.

A Dual-Band Transceiver with Excellent Heat Insulation Property for Microwave Absorption and Low Infrared Emissivity Compatibility

A Dual-Band Transceiver with Excellent Heat Insulation Property for Microwave Absorption and Low Infrared Emissivity Compatibility

Ultralight Biomass Aerogels with Multifunctionality and Superelasticity Under Extreme Conditions.

Biomass aerogels are highly attractive candidates in various applications due to their intrinsic merits of high strength, high porosity, biodegradability, and renewability. However, under low-temperature harsh conditions, biomass aerogels suffer from weakened mechanical properties, become extremely brittle, and lose functionality. Herein, we report a multifunctional biomass aerogel with lamella nanostructures (∼1 μm) fabricated from cellulose nanofibers (∼200 nm) and gelatin, showing outstanding elasticity from room temperature to ultralow temperatures (repeatedly bent, twisted, or compressed in liquid nitrogen). The resultant aerogel exhibits excellent organic solvent absorption, thermal infrared stealth, and thermal insulation performance in both normal and extreme environments. Even at dry ice temperature (-78 °C), the aerogel can selectively and repeatedly absorb organic solvents in the same way as room temperature with high capacities (90-177 g/g). Excellent heat insulation and infrared stealth performances are achieved in a wide temperature range of -196 to 80 °C. Further, this aerogel combines with the advantages of ultralow density (∼6 mg/cm3), biodegradability, flame retardancy, and performance stability, making it a perfect candidate for multifunctional applications under harsh conditions. This work greatly broadens application temperature windows of biomass aerogels and sheds light on the development of mechanically robust biomass aerogels for various applications under extreme conditions.

High-performance para-aramid paper strengthened by ultrafine fiber pulp of polyphenylene sulfide

Owing to its excellent heat resistance, lightness, insulation, and mechanical properties, aramid paper has been widely used in aerospace, rail transit, military, and other high-tech areas. With the rapid development of modern industries, para-aramid paper-based materials have become the development direction and trend of the specialty paper industry. In this study, para-aramid chopped fibers/polyphenylene sulfide (ACFs/PPS) composite paper sheets were fabricated by modern wet papermaking. The tensile strength, tensile index, and tear index of the hot-pressed ACFs/PPS composite paper sheets were substantially improved, reaching 103.5 MPa, 80.9 N m/g, and 119.1 mN m2/g under optimal speed of hot-pressing roller (0.2 m/min), hot-pressing temperature (310 °C), hot-pressing pressure (0.2 MPa), and ACFs content (70 wt%). The mechanical properties of hot-pressed ACF/PPS composite paper were markedly superior. Besides, the dielectric constant of the composite paper remained stable even when the temperature reached 100 °C. Briefly stated, ACFs/PPS composite paper exhibits desirable mechanical performance, thermostability, high breakdown strength, and low dielectric constant, delivering great potentials in the high-tech areas.