High Performance Thermal Insulation Research Articles

Natural fiber-based multifunctional aerogel with advanced oil absorption property and high thermal insulation performance

Designing an ultra-light and controllable structure for multifunctionality of low-cost aerogels is of great significance but remains a huge challenge because of the limitations of structural processability and mechanical vulnerability. Herein, we demonstrated a facile approach to synthesize a low-cost, ultralight, elastic, and highly recyclable superabsorbent from renewable fibers via environmentally friendly physical bonding and freeze-drying. Our approach introduces skin-core structure polyester (SPFs) into natural agriculture plant kapok, through which fibers entanglement and bonding to construct aerogel with adjustable hierarchical structure and desirable shapes. The resultant composite aerogel can be easily modified by organosilane, demonstrating durable superhydrophobicity (158.5°), advanced absorption capacity (128.4 g/g), good mechanical performance, self-cleaning, and thermal insulating (0.020 W/(m·K)). Therefore, the sustainable and multifunctional composite fibrous porous aerogels are potential materials for oil absorption applications and thermal management.

Ceramic Fiber-Reinforced Polyimide Aerogel Composites with Improved Shape Stability against Shrinkage.

Polyimide (PI) aerogels, renowned for their nano-porous structure and exceptional performance across a spectrum of applications, often encounter significant challenges during fabrication, primarily due to severe shrinkage. In this study, we innovatively incorporated ceramic fibers of varying diameters into the PI aerogel matrix to enhance the shape stability against shrinkage. The structure of the resulting ceramic fiber-reinforced PI (CF-PI) aerogel composites as well as their performance in thermal decomposition, thermal insulation, and compression resistance were characterized. The results revealed that the CF-PI aerogel composites dried by supercritical ethanol achieved greatly reduced shrinkage as low as 5.0 vol.% and low thermal conductivity ranging from 31.2 mW·m-1·K-1 to 35.3 mW·m-1·K-1, showcasing their excellent performance in shape stability and thermal insulation. These composites also inherited the superior residue-forming ability of ceramic fibers and the robust mechanical attributes of PI, thereby exhibiting enhanced thermal stability and compression resistance. Besides, the effects of different drying conditions on the structure and properties of CF-PI aerogels were also discussed. The coupling use of supercritical ethanol drying with the addition of ceramic fibers is preferred. This preferred condition gives birth to low-shrinkage CF-PI aerogel composites, which also stand out for their integrated advantages include high thermal stability, low thermal conductivity, and high mechanical strength. These advantages attribute to CF-PI aerogel composites substantial potential for a wide range of applications, particularly as high-performance thermal insulation materials for extreme conditions.

Advancing building fire safety through heat resistant and flame retardant hybrid silicone sealant

Rapid urbanization and population growth have led to a significant transformation in the urban landscape, characterized by the proliferation of high-rise buildings. However, this urban development has brought about new challenges, particularly in terms of fire safety. The escalating risk of disasters, especially fires, underscores the critical importance of implementing effective fire safety measures across all building types, necessitating legislative reforms. Despite their crucial role in ensuring structural integrity, sealants have often been overlooked in building safety standards, resulting in a lack of comprehensive regulations. The research addresses these challenges by focusing on the development of fire-resistant silicone sealants designed to enhance the fire resistance of building materials. These sealants were formulated independently, incorporating three fire retardants and four heat-resistant agents. While metal oxide flame retardants generally exhibited excellent performance, excessive mixing led to surface deformation and reduced workability. Optimal combinations of flame retardants and heat-resistant agents were identified, with the FR2 specimen demonstrating promising fire resistance performance. Full-scale fire performance tests conducted on FR2 revealed a maximum temperature difference of 40.6 °C between heated and unheated surfaces over a 2-h period, indicating high thermal insulation performance. These findings validate the efficacy of the proposed method and offer significant enhancements to building safety, thereby mitigating fire damage in urban environments.

A study on aramid nano-aerogel fiber and its fabric thermal conductivity

Aramid nano-aerogel represents an ideal structure for the fabrication of next-generation high-performance thermal insulation fibers and textiles. Single aramid nano-aerogel fiber can be achieved via wet spinning. The thermal conductivity of these fibers, a crucial determinant of textile insulation performance, remains under-explored in terms of numerical modeling. This research aims to establish a numerical inversion model to determine the thermal conductivity of single aramid nano-aerogel fiber. By simulating the three-dimensional geometry of plain fabric, the volume fraction of gas and solid within the fabrics are computed. Drawing from the law of energy conservation and Fourier's law of heat conduction, a relationship model is proposed between the thermal conductivity of single aramid nano-aerogel fiber and the overall thermal conductivity of the fabric. The finite difference method is employed to ascertain the thermal conductivity of single aramid nano-aerogel fiber. Furthermore, the influence of the geometric structure and the fiber diameter on the thermal insulation performance of the single-layer fabric is analyzed, which provides a feasible approach for the subsequent design of fabric structures with excellent thermal insulation properties.

Preparation of a novel bio‐based aerogel with excellent hydrophobic flame‐retardancy and high thermal insulation performance

AbstractSodium‐alginate‐based aerogels possess wide prospects in the fields of packaging, aerospace, industrial construction and transportation because of their environmental compatibility and thermal insulation, but it is still a challenge to obtain a sodium alginate‐based aerogel with high flame retardancy and good thermal insulation. Herein, a sodium‐alginate‐based aerogel with high flame retardancy, thermal insulation and good hydrophobic properties was prepared by two‐step crosslinking strategy of phytic acid and metal ions and liquid phase deposition of trans‐cinnamic acid. As a result, the prepared SA/PA Mn+ aerogels obtained excellent flame retardancy (UL‐94 V‐0, LOI 50.1%) and rapid self‐extinguishing, and SA/PA Mn+ aerogels obtained good hydrophobic ability (CA = 134.2°). In addition, the mechanical properties of SA/PA Mn+ aerogels have also been improved, the compressive modulus increased from 0.66 to 6.37 MPa, and the specific modulus increased from 15.7 to 140.2 MPa cm −3 g−1. This research broadens the application of bio‐based flame‐retardant aerogels in the fields of packaging, aerospace, industrial construction and transportation.

Multi-network PVA/SA aerogel fiber: Unveiling superior mechanical, thermal insulation, and extreme condition stability

Aerogels are highly sought-after in thermal insulation textiles due to their exceptional porosity and low density. However, Current research on aerogels mainly centers on their fixed two- and three-dimensional structures, lacking design flexibility, which significantly restricts their practicality. In contrast, one-dimensional aerogel fibers, while offering design flexibility, face complex fabrication, challenges in continuous molding, and pore collapse issues. In this study, utilizing polyvinyl alcohol (PVA) and sodium alginate (SA) as raw materials, a cost-effective wet spinning, freeze-thaw cycling, and freeze-drying technique were employed to continuously produce multi-functional PVA/SA aerogel fibers with a stable network pore structure through the design of a multi-crosslinked interlocking network structure. The optimal preparation process for the aerogel fibers was explored and characterized. The resulting aerogel fibers exhibited a stable hierarchical pore structure at the microscale, featuring large pores, nested mesopores, and micropores. These fibers possessed a high specific surface area (115.88 m²/g), high porosity (92.42 %), low density (0.0632 g/cm³), low thermal conductivity (0.0378 W/(m·K)), and flame resistance (LOI: 26.8 %). Furthermore, their stable internal network scaffold structure endowed them with outstanding mechanical properties (3.6 cN/tex) and stability in extreme environments. These composite aerogel fibers offer great potential for high-performance thermal insulation textiles and products.

Performance analysis on a wood-color thermal catalytic Trombe wall in wood buildings

The wood buildings had huge advantages such as high thermal insulation performance and carbon fixation. While the indoor air pollution caused by the release from volatile organic compounds (VOCs) from the artificial boards in wood buildings creates huge threat on human health. Considering architectural aesthetics and solar building-integration principles, this article proposed a novel thermal catalytic Trombe wall with wood-color thermal catalysts that realized heating and air purification. Firstly, the color difference between thermal catalysts and wood board was analyzed. Secondly, the heat and mass transfer model of the wood building with Trombe wall was developed and verified. Thirdly, the thermal and purification performance under different occupancy ratios of Trombe wall to whole wall (RT) and wood species were discussed. The main results were: (1) The color difference between thermal catalysts and wood was 0.97, which was similar and acceptable to meet architectural aesthetics; (2) Compared to ordinary wood building, the indoor temperature increased by 18 ℃ when combined with Trombe wall. The average thermal efficiency, purification efficiency and generated clean air were 26.91 %, 94.34 % and 385.58 m3, respectively. (3) With the increase of RT, the formaldehyde degradation performance and indoor air temperature increased from 73.52 % to 94.34 %, 25 to 38 ℃, respectively. (4) When considering natural running in daytime and forced running in nighttime, more than 90 % of indoor formaldehyde was degraded for five wood boards with different formaldehyde emission rates. The indoor formaldehyde concentration would be below 80 ppb for the release rate of 0.98 and 1.40 mg/L.

Hollow glass microsphere/polydopamine/glass fiber reinforced composites with high thermal insulation performance by inhibiting conductive and radiative heat transfer

Glass fiber-reinforced polymer (GFRP) is commonly used as an insulating lightweight material because of low thermal conductivity. Due to the increasing demand for lightweight composites with the extreme thermal insulation properties, a highly insulating composite was proposed with inhibiting both conductive and radiative heat transfer. We embedded hollow glass microspheres (HGMs), as a conductive heat transfer inhibitor, onto glass fiber by leveraging the adhesive properties and black color of polydopamine, as a radiative heat transfer inhibitor. The new GFRP integrated with polydopamine and HGMs improved thermal insulation properties by 14 % compared with neat GFRP and infrared blocking performance while increasing interlaminar and impact strengths by 48.7 %, 28.4 % and maintaining similar tensile and compressive strengths. Moreover, it improved flame retardant properties with 27.1 % reduction in heat release rate and 25 s of ignition time delay. Based on the excellent multi-functions, it can be applied to industries such as cryogenic container parts.

Unusual flexibility of transparent poly(methylsilsesquioxane) aerogels by surfactant-induced mesoscopic fiber-like assembly

High-performance thermal insulators represented by aerogels are regarded as one of the most promising materials for energy savings. However, significantly low mechanical strength has been a barrier for aerogels to be utilized in various social domains such as houses, buildings, and industrial plants. Here, we report a synthetic strategy to realize highly transparent aerogels with unusually high bending flexibility based on poly(methylsilsesquioxane) (PMSQ) network. We have constructed mesoscopic fine fiber-like structures of various sizes in PMSQ gels by the combination of phase separation suppression by tetramethylammonium hydroxide (TMAOH) and mesoscopic fiber-like assembly by nonionic poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-b-PPO-b-PEO) type surfactant. The optimized mesoscale structures of PMSQ gels have realized highly transparent and resilient monolithic aerogels with much high bendability compared to those reported in previous works. This work will provide a way to highly insulating materials with glasslike transparency and high mechanical flexibility.

Ultrastrong and High Thermal Insulating Porous High-Entropy Ceramics up to 2000°C.

High mechanical load-carrying capability and thermal insulating performance are crucial to thermal-insulation materials under extreme conditions. However, these features are often difficult to achieve simultaneously in conventional porous ceramics. Here, for the first time, it is reported a multiscale structure design and fast fabrication of 9-cation porous high-entropy diboride ceramics via an ultrafast high-temperature synthesis technique that can lead to exceptional mechanical load-bearing capability and high thermal insulation performance. With the construction of multiscale structures involving ultrafine pores at the microscale, high-quality interfaces between building blocks at the nanoscale, and severe lattice distortion at the atomic scale, the materials with an ≈50% porosity exhibit an ultrahigh compressive strength of up to ≈337MPa at room temperature and a thermal conductivity as low as ≈0.76W m-1 K-1. More importantly, they demonstrate exceptional thermal stability, with merely ≈2.4% volume shrinkage after 2000°C annealing. They also show an ultrahigh compressive strength of ≈690MPa up to 2000°C, displaying a ductile compressive behavior. The excellent mechanical and thermal insulating properties offer an attractive material for reliable thermal insulation under extreme conditions.

Carbon/ZrO2 aerogel composite microtube superfoam.

High-performance thermal insulation materials with broad application prospects have attracted great attention. The introduction of new microstructures into thermal protection materials can significantly improve the thermal insulation performance. The tubular microstructure has obvious advantages such as thermal insulation, lightweight, mechanical, and other properties. Therefore, the microtubular structure has become an important reference microstructure for the development of high-performance thermal insulation materials. In this paper, the carbon/ZrO2 aerogel composite microtube superfoams with excellent thermal protection properties were prepared by a vacuum filtration and high-temperature carbonization method. The ZrO2 aerogel precursor solution can be quickly and uniformly adsorbed on the inner and outer walls of cellulose microtubules. These adsorbed ZrO2 aerogel precursor solution films can be converted into ZrO2 alcohol gel shells under the acceleration and promotion effect of citric acid at 65 °C. The micromorphology of the ZrO2 aerogel shell on the inner and outer walls of the composite microtubes can be efficiently controlled by the concentration of the ZrO2 aerogel precursor solution and the carbonization temperature. The carbon/ZrO2 aerogel composite microtube superfoam exhibits a lower thermal conductivity, lower density, good mechanical properties, and high ablation resistance. The thermal conductivity of the carbon/ZrO2 aerogel composite microtube superfoam is as low as 0.040 ± 0.001 W m-1 K-1. The residual rate of the carbon/ZrO2 aerogel composite microtube superfoam is still as high as 84.33% after butane flame ablation for up to 3600 seconds.

Direct Synthesis of Polyimide Curly Nanofibrous Aerogels for High-Performance Thermal Insulation Under Extreme Temperature.

Maintaining human body temperature is one of the basic needs for living, which requires high-performance thermal insulation materials to prevent heat exchange with external environment. However, the most widely used fibrous thermal insulation materials always suffer from the heavy weight, weak mechanical property, and moderate capacity to suppress heat transfer, resulting in limited personal cold and thermal protection performance. Here, an ultralight, mechanically robust, and thermally insulating polyimide (PI) aerogel is directly synthesized via constructing 3D interlocked curly nanofibrous networks during electrospinning. Controlling the solution/water molecule interaction enables the rapid phase inversion of charged jets, while the multiple jets are ejected by regulating charge density of the fluids, thus synergistically allowing numerous curly nanofibers to interlock and cross-link with each other to form porous aerogel structure. The resulted PI aerogel integrates the ultralight property with density of 2.4mg cm-3, extreme temperature tolerance (mechanical robustness over -196 to 300 °C), and thermal insulation performance with ultralow thermal conductivity of 22.4mW m-1 K-1, providing an ideal candidate to keep human thermal comfort under extreme temperature. This work can provide a source of inspiration for the design and development of nanofibrous aerogels for various applications.

Efficient thermal insulation through all-biomass silk fibroin composite aerogel 3D-reinforced by natural down-fiber

Biomass-based aerogels offer numerous individual benefits in thermal insulation applications. However, their generally weak mechanical properties impair the further development of aerogels. Herein, natural down-fiber (DF) reinforced silk fibroin (SF) all-biomass aerogel was rationally designed. The developed 3D-reinforcement structure, in which DF was physically interspersed in SF in multiple directions and hydrogen bonds formed between DF and SF, resulted in significantly enhanced compression stress of 146.3 kPa (3.44 times greater than that of SF aerogel, which attained 42.57 kPa) and impressive compression resilience. Meanwhile, the DF@SF aerogel displayed a hierarchical porous structure (97.64 % porosity) with micron-sized holes and nano-sized pores, as well as low thermal conductivity of 0.034 W m−1 K−1, which would effectively inhibit air circulation and limit heat transfer for improved thermal insulation. Moreover, the addition of DF reduced the average hole diameter, which further prevented heat convection and minimized heat radiation inside the aerogel. As a result, the DF@SF aerogel demonstrated excellent thermal insulation performance with a wide range of working temperatures from −40 to 160 °C and stability for recyclable usage. Therefore, this all-biomass DF@SF aerogel could offer an alternative form of high-performance thermal insulation. This strategy will also inspire more research into the construction of 3D-reinforced functional aerogels and their applications in thermal insulation, sound insulation, biomedicine, and other related areas.

Promising biomass waste–derived insulation materials for application in construction and buildings

AbstractCurrent insulation materials applied in construction engineering and the building industry are generally petrochemical-based polymers and recycled thermal insulation materials. The environmental effects of these materials’ production processes are substantial, despite their high thermal insulation performance. Consequently, the researchers conclude that it is essential to develop and produce insulating materials with superior thermal properties, minimal environmental impact, and a reasonable cost. The study concentrated on the application of insulation materials derived from biomass in the development of thermal insulation. The purpose of this review is to investigate and develop the possibilities of using biomass wastes as renewable and eco-friendly thermal insulation materials for construction engineering and the building industry. The thermal conductivity of those materials was measured using the hot plate and hot box methods, two of the most widely used hot processing methods. With a relatively low thermal conductivity (< 0.100 W·m−1·K−1), this review provides critical scientific insight into potential building insulation materials derived from biodegradable and abundant resources. It was observed that these materials are appealing for use in building and construction because they have a number of potential advantages from technical, economic, environmental, and green credentials perspectives. The collection of information enables some conclusions regarding the different biomass waste–derived insulation materials that have already been investigated and identifies gaps in the literature. Finally, the scope of commercialization pathways and future research directions to validate the proposed material alternatives’ claim for commercial-scale applications has been identified in this review. Graphical Abstract

Highly porous YSZ ceramic foams using hollow spheres with holes in their shell for high-performance thermal insulation

Highly porous YSZ ceramic foams using hollow spheres with holes in their shell for high-performance thermal insulation

Low shrinkage polyimide aerogels with excellent thermal insulation: Boosted by “paddle-shaped” benzhydrylidenefluorene-based diamines

Polyimide (PI) aerogels are widely employed as thermal insulating materials in the aerospace and transportation industry in extreme environments. However, there is a lack of research that focused on the development of novel monomers for the preparation of high-performance PI aerogels. In this study, we proposed a “rigid-soft” strategy to design structurally unconventional diamine compounds. These compounds effectively enhance the rigidity of the PI chain, leading to improved thermostability, while still maintaining flexibility and moderate mechanical properties. Accordingly, two brand-new monomers (BDFD and BDFA) incorporating a twisted “paddle-shaped” benzhydrylidenefluorene (BDF)-based diamine were successfully developed. These monomers consisted of a flexible diphenylmethylene moiety coupled to a rigid fluorene building block. Leveraging these distinctive characteristics, two series of PI aerogels were prepared and exhibited exceptional performance, including a low shrinkage rate, high surface area, and uniform pore size. Notably, the PI-D1 aerogel, composed entirely of BDFD, demonstrated the highest surface area of 674.8 m2 s−1. With a molar ratio of 1/3 for BDFA/ODA, PI-A4 demonstrated the ability to achieve high-performance thermal insulation (54.3 mW m−1 K−1 at 200 °C) with excellent thermostability (Td 5% > 580 °C, Tg > 299 °C) and satisfactory dimensional stability (shrinkage at 7.7 %), thanks to its smaller pore size (∼24 nm) and well-balanced rigid and flexible structure property. This research provides an effective method for creating high-performance PI aerogels with an exceptionally low shrinkage rate, which makes them appropriate for thermal management materials that require superior thermal insulation properties.

Enhancing battery module safety with insulation material: Hollow glass microspheres incorporating aerogel of varying particle sizes

Thermal runaway propagation (TRP) in lithium-ion batteries (LIBs) poses a critical safety concern, hindering their widespread application. In this study, we present a novel thermal insulation material designed to effectively mitigate TRP in LIBs. The material comprises a mechanical support framework consisting of hollow glass microspheres (HGMs) and acrylic emulsion, filled with aerogel particles (APs). We systematically investigate the influence of HGMs and APs addition on the properties. The findings reveal a positive correlation between HGMs and mechanical properties, as well as APs and thermal insulation properties, at appropriate addition levels. The optimal insulation material exhibits exceptional compressive strength (1.42 MPa), achieves a UL-94 V-0 flame retardancy rating, and demonstrates high thermal insulation performance (44.3 mW·m−1·K−1). Moreover, we explore the impact of strain on thermal insulation performance, observing a gradual increase in thermal resistance loss with higher strain. Notably, even at a strain of 70 %, the thermal conductivity experiences only a modest increase from 44.3 to 52 mW·m−1·K−1. Additionally, we evaluate the effect of APs size on the material's properties, finding that decreasing particle size from 50 to 5 μm leads to a reduction in mechanical properties (1.42 to 1.12 MPa) but an improvement in thermal insulation performance (44.3 to 39.7 mW·m−1·K−1). Finally, we validate the practical efficacy of the insulation material in preventing TRP through the use of a 2 mm thickness. This study presents a promising approach to enhance the safety of LIBs by developing an efficient insulation material with outstanding properties.

Preparation of SiO2/Fe2O3 composite aerogels for thermal insulation enhancement

Silica aerogel, with a unique nano-network structure, serves as a high-performance thermal insulation material. However, silica aerogel possesses a high infrared wave transmission ratio above 300 °C, whose thermal conductivity increases and thermal insulation performance further decreases with the increasing temperature. Introducing opacifiers to silica aerogel is a crucial strategy for addressing this issue. In this work, the ferric oxide exerted as an opacifier was incorporated into the main-phase silica aerogel to improve its thermal insulation at high temperatures. The SiO2/Fe2O3 composite aerogels were created via the two-step sol-gel process followed by supercritical drying, which involved doping ferric nitrate nonahydrate as a Fe2O3 precursor into the silica sol generated with tetraethoxysilane. In this way, SiO2/Fe2O3 composite aerogels with low density (0.04 g/cm3), high specific surface area (705 cm2/g), and low thermal conductivity (0.026 W/(m K)) were obtained by structural adjustment. The incorporation of Fe2O3 improves the thermal insulating properties of silica aerogels. After heat treatment at 1100 °C, the thermal conductivity of the SiO2/Fe2O3 composite aerogel was 0.167 W/(m K), lower than that of the pure silica aerogel (0.249 W/(m K)). Furthermore, the SiO2/Fe2O3 composite aerogel maintained its amorphous structure and exhibited a specific surface area of approximately 94.56 cm2/g, which was three times that of the pure silica aerogel. When subjected to 5-min heating at 1000 °C, the maximum surface temperature of the heat delivery surface of the SiO2/Fe2O3 composite aerogel reached 280.8 °C, whereas the pure silica aerogel reached 353.8 °C.

Preparation of DOPO-KH550 modified hollow glass microspheres/PVA composite aerogel for thermal insulation and flame retardancy

The creation of high-performance thermal insulation and flame-retardant materials is of great importance for minimizing energy consumption and reducing fire risk for modern buildings. Herein, we report the creation of a new composite aerogel, which was prepared by incorporation of 9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-Oxide-3-Aminopropyl triethoxysilane (DOPO-KH550) modified hollow glass microspheres (HGM) into polyvinyl alcohol (PVA) using citric acid as a cross-linker, as a kind of thermal insulation and flame retardant materials (abbreviated as PVA-DKHGM). The as-synthesized PVA-DKHGM composite exhibits superior thermal conductivity of 0.0187 W m−1 K−1, owing to the hollow structure of the hollow glass microspheres and rich porosity. Besides, it reaches V-0 level at the UL-94 test and the peak heat release rate (pHRR) was measured to be 114.93 (kW/m2) which is lower than most composites now. These results are attributed to the synergy effect of the hollow glass microsphere and DOPO-KH550 which offers the composites aerogel excellent flame retardancy. Owing to its advantages such as lightweight, highly porous, thermally stable, simple to prepare, high mechanical strength, and can be further scaled up, our PVA-DKHGM aerogel may hold great potential for practical applications in construction of energy-saving modern buildings.

Fabrication of organic based thermal resistance material using pyrolyzed cellulose nanofiber and carbon fiber for high performance thermal insulation

Herein, polymer-based thermal insulating composites are fabricated using pyrolyzed cellulose nanofiber (p-CNF) and carbon fiber (CF) in order to overcome the existing limitations of organic-based thermal resistance materials. The p-CNF is prepared by iodine treatment and calcination. The pyrolyzed CNF/CF composites are then fabricated via the freeze casting of two-dimensional (2D) CFs to obtain a low thermal conductivity of 0.058 W/mK, along with a high thermal stability, high tensile stress. Therefore, the p-CNF/CF composite provides an efficient thermal insulation performance via low thermal conductivity along with a high thermal degradation temperature, thereby demonstrating the potential for the development of thermal resistance materials.