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• Elaborate and characterize new ecological acoustic absorbers/sound insulation panels and thermal insulation panels. • Acoustic and thermal properties were measured experimentally using standardized methods. • Morphological analysis of the different fibers was carried out using scanning electron microscopy. • Bulk density, air flow resistivity and water absorption were measured experimentally. • The new panels are good candidates for the development of local materials with the required acoustic and thermal properties. This work aims to elaborate and characterize new ecological composite materials from cardboard waste and abandoned natural fibers for the manufacture of local acoustic absorbers/sound insulation panels and thermal insulation panels. For this purpose, twenty-eight samples were prepared by mixing a mass fraction of 60 % of cardboard waste and 40 % of natural fibers available in the south-east region of Morocco, i.e. Doum, Wheat straw, Reed, Esparto, Bagasse, Fig, and Olive. Firstly, the morphological analysis of the different fibers was carried out by scanning electron microscopy (SEM). Secondly, the acoustic and thermal properties were measured experimentally using standardized methods. In addition, bulk density, air flow resistivity and water absorption were measured. The experimental results showed that the studied panels have good acoustic and thermal performances. The sound absorption coefficient, sound transmission loss, bulk density, thermal conductivity, and heat capacity were in the range of 0.4–0.8; 20–45 dB; 278.6–343.8 kg/m3; 0.072–0.10 W/m.K; 1254.5–1807.5 J/kg.K, respectively. Consequently, the new panels developed in this study are good candidates for the development of local materials with the required acoustic and thermal insulation properties for applications in buildings. Their main advantages are: low environmental impact, low cost, and they can even compete with commercialized synthetic materials. [ABSTRACT FROM AUTHOR]

• Lightweight, flexible aerogels using renewable curdlan and wood waste chips as raw materials. • Low thermal conductivity (30.1 × 10−3 W/(m·K)) and high thermal stability up to 300 °C. • Hydrophobic and good compression-resilience behavior. Developing flexible and lightweight materials with elevated thermal insulation performance from renewable biomass is significant for green and sustainable energy. In this work, a multifunctional biomass aerogel using wood waste as a raw material is proposed. The composite aerogel consists of curdlan as a structural framework, wood fibers and nano-hydroxyapatite as reinforcing phases. By employing thermogravimetry (TG), infrared thermal imager and thermal conductivity tester, the thermal stability and thermal insulation performance of the aerogel were evaluated. The consequent thermal conductivity reaches 30.1 × 10−3 W/(m·K). As the strength and toughness of the aerogel is improved by introducing cellulose into the matrix, it shows a maximum compressive modulus of 1.65 MPa. The hydrophobicity of the aerogel is achieved by an alkylation method and the contact angle is over 120°. This nontoxic aerogel composite with high thermal and mechanical performance indicates a potential utilization in the thermal management of food and electronic industry. [Display omitted] [ABSTRACT FROM AUTHOR]

• Phenolic resin aerogel is synthesized from linear and boron phenolic resin. • The ultralow shrinkage attributes to the strong B-O bond in boron phenolic resin. • Thermal conductivity of aerogel with a density of 0.105 g/cm3 is 0.0352 W/(m·K). • Aerogel shows excellent mechanical stability and resilience capacity. Lightweight phenolic resin aerogel with excellent thermal insulation and mechanical properties is an attractive material for thermal engineering applications. However, to synthesize such material, generally, a significant volume shrinkage would occur during the aerogel formation and the processing time is long. To conquer such issues, the lightweight phenolic resin aerogel with excellent thermal insulation and mechanical properties was synthesized by an elaborately designed process, where linear thermoplastic phenolic resin (LPR) and boron-modified thermosetting phenolic resin (BPR) were used as the raw materials. It was found that the shrinkage rate and the processing time of the phenolic resin aerogel were significantly reduced. By optimizing the synthesis process, the aerogel with a density of 0.105 g/cm3 and a thermal conductivity of 0.0352 W/(m·K) was achieved. [ABSTRACT FROM AUTHOR]

Rigid polyimide foams (PIFs) with excellent mechanical and thermal properties were fabricated by thermal foaming of active cross-linkable units terminated polyester ammonium salts (PEAS) precursor powders. The active cross-linking strategy was realized by breaking C C bonds in maleic anhydride under heating treatment. Results showed that the formation of cross-linked structure before complete imidization effectively resisted matrix shrinkage and endowed PIFs with outstanding mechanical properties. The room temperature compressive strength and modulus of PIFs with four repeating units reached as high as 2.34 and 56.1 MPa, respectively. Moreover, the PIFs exhibited excellent thermal properties with onset decomposition temperatures ranging from 490 to 550 °C and the glass transition temperatures exceeding 290 °C. The PIFs displayed better thermal insulation, and the values of thermal conductivity fell within a range of 0.056–0.090 W m−1 K−1, which demonstrates potential application as high temperature resistant structural materials in aerospace and energy sectors. [Display omitted] • Rigid PIFs were fabricated by thermal foaming of active cross-linkable units terminated PEAS precursor powders. • Cross-linking structure was formed before complete imidization which endowed PIFs with outstanding mechanical properties. • Relationship between chain structure and properties of rigid PIFs were investigated. [ABSTRACT FROM AUTHOR]

• Preparation of Casein based zinc oxide nanocolloids using the two-step approach. • Thermal diffusivity studies of prepared samples using dual-beam thermal lens techniques. • Tunable behavior of thermal diffusivity depending on volume fraction and morphology. Nanofluids with suitable heat transfer properties were found to be applied in thermal insulators, transport, nanodevices, medicine, etc. Their heat transfer properties are influenced by the particle size, morphology, and concentration of the nanoparticles present in the nanofluids. Nanofluids of different morphologies of zinc oxide such as nanospheres, nanoflowers, and nanorods were synthesized and their thermal properties were evaluated using a dual-beam thermal lens technique. All these nanofluids were found to exhibit tunable thermal diffusivity depending on concentration. The nanofluids with flower-like morphology show maximum deviation in diffusivity due to the layered structure and the increased surface area. As compared to pristine zinc oxide nanofluids, casein-capped zinc oxide nanofluids show excellent thermal insulation properties at 60 μg/ml. The findings suggest that biofunctionalized zinc oxide nanofluid is a promising candidate for a variety of thermal applications. [ABSTRACT FROM AUTHOR]

Rape straw as a waste product of the oilseed industry is available abundantly in the European Union. In this paper, the utilization of rape straw-based fibers for the preparation of binderless thermal insulation materials is investigated. The effect of steaming temperature, which can be considered as one of the most important parameters of the production process, on microstructure and mechanical, hygric and thermal properties of the insulation boards is analyzed. The experimental results show that the designed binderless rape straw fiberboards achieve the most suitable combinations of mechanical, hygric and thermal properties for the steaming temperatures of 180 °C and higher, which indicates 180 °C as the most promising solution. • Binderless rape straw fiberboards with a bulk density of 100 kg/m3 were designed. • The effect of steaming temperature is analyzed. • Thickness swelling decreased substantially with increasing steaming temperature. • The most suitable properties achieved fiberboards produced at 180 °C and 200 °C. • The thermal conductivity was within the range of 0.045–0.052 W/mK. [ABSTRACT FROM AUTHOR]

Epoxy (EP) resin insulations are widely used in electronic devices and power systems. They are gradually finding their way as winding insulation material for medium frequency transformers (MFT) due to their attractive insulating and adhesive properties along with low cost and easy processing. However, their dielectric insulation properties are compromised at high frequencies and high temperatures due to poor thermal properties. In this context, the surface-treated hexagonal boron nitride (h-BN) micro fillers and core-shell TiO 2 @SiO 2 nanofillers are doped in epoxy (EP) to enhance their thermal and electrical insulation properties under high frequencies and high temperatures. Results reveal that the thermal conductivity of the EP increases continually, whereas the electrical breakdown strength is reduced above the threshold content of micro/nano fillers. Particularly, the micro h-BN addition is beneficial for thermal conductivity enhancement, whereas the core-shell structure of TiO 2 @SiO 2 improves the electrical insulation properties of the EP. The multi-layer core model is used to explain the dynamics of the fillers. The homogeneous dispersion and optimal content of suitable micro-nano fillers can produce efficient EP composites as the electrical insulation for medium frequency transformers. [Display omitted] [ABSTRACT FROM AUTHOR]

• The chemical grafting of ammonium polyphosphate onto the surface of HGM was reported for the first time. • Composites aerogel have excellent thermal insulation properties. • Composites aerogel have excellent flame retardancy, and the LOI value is as high as 100. • Composites aerogel have good mechanical properties. The development of high-performance flame-retardant materials with better thermal insulation properties is of great significance to modern building energy conservation. In this study, we report the facile and scalable fabrication of novel aerogels (SA-HGM-APP) based on the building blocks of ammonium polyphosphate (APP) coated hollow glass microspheres (HGM) and matrix material sodium alginate (SA) by freeze drying method. The as-prepared composite aerogel exhibits better thermal stability (decomposition temperature over 210°C). In addition, SA-HGM-APP composite aerogels have good thermal insulation properties and low thermal conductivity, which is 0.035 W m−1 K−1. More importantly, the peak heat release rate (pHRR) is 14.14 kW m−2, the limiting oxygen index (LOI) value is as high as 100%, and the aerogel composite material can reach UL-94 V-0 grade, so it shows excellent flame retardancy. These results attributed to a synergistic effect, which combines the rich porous structure derived from HGM, so that SA and APP have better thermal insulation and excellent non flammability, thus providing excellent flame retardancy. SA-HGM-APP aerogel composite has many advantages, such as simple preparation method and high mechanical strength. It has great potential in future thermal insulation and flame retardancy applications. [ABSTRACT FROM AUTHOR]

The novel multifunctional lightweight composites (MLCs) reinforced with integrated preform were prepared for thermal protection system (TPS) of hypersonic vehicles in extreme aerothermodynamic environment. The high-temperature behavior including thermal physical properties decomposition performance, and the ablation resistance were tested by the oxy-acetylene torch system, as well as the micro-morphologies of MLCs from non-destructive testing were investigated. An integration factor was proposed to evaluate the comprehensive performance of MLCs. The results show that MLCs had high structural efficiency without delamination and defelting, excellent thermal insulation performance, and superior ablation resistance ability. The comprehensive performance of MLCs had obvious advantages to polymer-matrix composites (PMCs). The novel MLC reinforced with integrated preform can help for the development of thermal protection materials of hypersonic aircrafts. [ABSTRACT FROM AUTHOR]

Geopolymers have been a frequently studied topic during the last decades due to waste materials utilization, low energy demands, and low carbon dioxide emissions related to their production, which makes them very attractive within the current environmental trends. However, the original idea to use them as a concrete replacement showed to be unattainable in the nearest future, so other alternatives of geopolymers applications are being sought that could exploit the efforts spent and research progress made so far. This review paper summarizes the recent progress in the field of directly foamed geopolymers, as one of the alternatives, focusing on the material base, foaming and stabilization processes, and assessments of selected material parameters, as related to raw materials used and treatment techniques applied. As the main result, several gaps and challenges are identified that deserve more attention and deeper investigations, which can help to move the geopolymer foams closer towards their regular application in civil engineering. A detailed knowledge of hygric parameters and their influence on thermal properties, long-term performance analyses in real-world applications, or extension of the material base to achieve environmental more friendly solutions represent the most topical issues that are supposed to be addressed. • Recent progress in the field of directly foamed geopolymers is reviewed. • Foaming and stabilization processes are analyzed. • Material parameters are assessed and linked to raw materials and treatment techniques. • An overview of durability of geopolymer foams is given. • Several gaps in the current knowledge are identified that require deeper investigations. [ABSTRACT FROM AUTHOR]

• Graphene/Fe3O4 hybrid aerogel were prepared by self-assembly synthesis. • The effects of concentration of nano-Fe3O4 in the aerogel were studied. • Mechanical and thermal properties of the hybrid aerogels were investigated. [Display omitted] Graphene aerogel and graphene-magnetite hybrid aerogel were prepared using hydrothermal method followed by a freeze-drying process. Magnetite nanoparticles were encapsulated by graphene sheets in an electrostatic self-assembly process. The morphology and properties of aerogels were characterized by several techniques including UV-Vis spectroscopy, Raman spectroscopy, FESEM, TEM and XRD. The mechanical and thermal behavior of the aerogels were evaluated at different concentration levels of Fe 3 O 4 nanoparticles (0, 10, 20 and 30 wt%). The compressive strengths of the hybrid aerogels at the strain of 80% for graphene aerogels containing 0, 10, 20 and 30 wt% Fe 3 O 4 nanoparticles were determined to be 5.93, 12.96, 6.85, and 6.15 kPa, respectively. The highest mechanical properties were achieved for the sample containing 10 wt% Fe 3 O 4 nanoparticles (FGA10). Thermal analysis revealed that FGA10 sample had a 15% less weight loss when heated up to 600 °C compared with that for the bare graphene aerogel, indicating the formation of a more thermally stable structure. Furthermore, adding Fe 3 O 4 nanoparticles improved the thermal insulation performance of the graphene aerogel, since the dynamic heat transfer rate and heat dissipation rate of FGA10 were lower than those for the bare graphene aerogel. [ABSTRACT FROM AUTHOR]

• A new method to obtain hierarchical material microstructures is proposed. • The weight coefficients can be adaptively adjusted during the optimization. • Good connectivity and clear interfaces between two materials are always maintained. • This method is universal, high efficiency, program easiness and good connectivity. Composite materials with multiple properties are important for a range of engineering applications. Hence, this study focuses on topological design of hierarchical materials with multiple performance in both thermal insulation and mechanics. First, a novel multi-objective optimization function is defined to find a solution from the Pareto frontier, where the weight coefficients can be adjusted adaptively, to keep all the individual objective functions and their sensitivities stabilized at the same level during the optimization. Second, a new design strategy is proposed to achieve the hierarchical designs of biphasic material microstructures, they are periodically arranged by the porous base materials that are known in advance and independent of topology optimization. Third, sensitivity information and algorithm implementation are given in detail, and the bi-directional evolutionary structural optimization method is adopted to iteratively update the micro-structural topologies, by combining with the homogenization method. Last, numerical examples are provided to illustrate the benefits of the proposed design method, such as high efficiency, implementation easiness, good connectivity and clear interface between adjacent phases, etc. [ABSTRACT FROM AUTHOR]

A novel naturally grown mycelium-composite insulation brick was bio-produced by cultivating a biocompatible and fast-growing fungus, Pleurotus ostreatus , in the rye berries feedstocks. The resultant mycelium composites consisted of a core of colonized substrate, encased by a layer of water-repellent fungal skin. The microstructure of mycelium composites shows that fungal fibers grow from feedstocks and bonded adjacent feedstocks. The impact of density and moisture on the mechanical properties of mycelium composites were studied, finding that composites with increased density presented an improvement of flexural strength under both low and middle levels of Relative Humidity (RH). However, under high level of RH, composites have a lower flexural strength but a greater deformation. The mechanical strength of mycelium composites, however, meets the existing transportation and construction requirements. Based on the measured thermal properties of mycelium composites, EnergyPlus analyses were conducted to evaluate their performance in buildings' operational energy in comparison with conventional natural insulation materials, i.e., lightweight expanded clay aggregate (LECA) and expanded vermiculite (EV). Compared with LECA and EV, the use of mycelium-composite for building insulation reduced the indoor temperature fluctuations. Compared with LECA and EV, mycelium-composite insulation reduced the total annual heating and cooling energies as well as the total annual CO 2 emissions for buildings located in US Climate Zone 2–8, with the only exception being in Zone 1 or the very hot climate zone. Therefore, naturally grown mycelium-composite, as demonstrated in this study, is promising to provide sustainable building insulation materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Low cost and high performance. • Silica aerogel fabricated from incineration bottom ash. • Thermal insulation paint with silica aerogel additive. • 12 °C surface temperature reduction improvement on the heated plate at 60 °C. • 1 °C in-chamber temperature reduction with external temperature of 44.6 °C. In this work, silica aerogel (SA) powder is fabricated through a sustainable method from incineration bottom ash. The fabricated SA has a low thermal conductivity of 0.025 W/mK, high surface area of 786 m2/g, and high porosity of 96.36%. The thermal analysis of SA powder shows it has a stable hydrophobicity up to 418 °C. The SA powder has been mixed into water-based paints to develop a high efficient thermal insulation paint with inproved thermal insulaton properties. Different percentage of SA were mixed into the paint samples to prepare the silica aerogel thermal insulation paint (SATIP) and their physical properties were studied. The SATIP samples were then coated on cement board substrates. The thermal conductivity, water resistance, durability and insulation performance of the samples were investigated and evaluated systematically. The scrub resistance of SATIP can be improved significantly by 219% after adding 5 vol% SA powder. And by adding 20 vol% of SA into the SATIP, it achieves up to 12 °C surface temperature reduction improvement compare to the one without SA on the heated plate at 60 °C, and 1 °C in-chamber temperature reduction with external temperature of 44.6 °C. The spectral reflectance analysis demonstrates that the improvement of the thermal insulation performance of the SATIP is attributed to the thermal insulation property of SA and proves that the developed SATIP is color insensitive and has wider applications. The results demonstrated a low-cost and scalable process fabricates SA with superor properties. The developed SATIP has a great potential for application in sustainable and green buildings for energy saving. [ABSTRACT FROM AUTHOR]

• To achieve the desired printability, the optimal replacement range for silica sand by aerogel in a cementitious mixture is 0–20% by volume. • The thermal conductivities of the SC and 3D printed specimens ranked in the order of 3DCP-X > SC > 3DCP-Y > 3DCP-Z, irrespective of aerogel content. • The weak bonding interfaces between adjacent filaments produce gaps, providing channels for heat to transfer in specimens 3DCP-X. • Under the same thermal and mechanical requirements, walls fabricated by AG-incorporated concrete are 7-cm thinner than traditional concrete walls. This study investigated the properties of fresh and hardened aerogel (AG)-incorporated concrete suitable for 3D concrete printing. After trial and error, it was found, that to achieve the desired printability, the optimal replacement range for silica sand by aerogel in a cementitious mixture is 0–20% by volume. The physical, mechanical, and thermal insulation properties of hardened concrete in three directions were studied, and the influence of anisotropy on these properties was investigated. The results showed that irrespective of the aerogel content, the compressive strength of the cast specimens (avg. 24.90 MPa in A20) was slightly higher than those of the 3D printed specimens, 3DCP-X (avg. 23.63 MPa in A20), 3DCP-Y (avg. 20.77 MPa in A20), and 3DCP-Z (avg. 20.40 MPa in A20). The thermal conductivity of the cast and printed specimens decreased gradually with an increase in the aerogel content. Relative to that of the cast specimens (0.330 W/(m·K) in A20), the thermal conductivity of specimens 3DCP-X (0.405 W/(m·K) in A20) was slightly higher, while those of 3DCP-Y (0.320 W/(m·K) in A20) and 3DCP-Z (0.306 W/(m·K) in A20) were lower. A thermal insulation wall (400 mm × 200 mm × 600 mm) with hollow structures was printed using the AG-incorporated concrete. To satisfy the same thermal and mechanical requirements, walls fabricated using AG-incorporated concrete can be 7 cm thinner than traditional concrete walls. The mechanism for the heat transfer of AG-incorporated concrete in three directions was examined as well. [ABSTRACT FROM AUTHOR]

• Unidirectional anisotropic PIAs have been prepared by freeze-drying. • The PIA shows excellent thermal stability and stable mechanical behavior. • The u -PIA-6 exhibits great strength, which is over twice as high as that of the TEEK-HH at 177 °C with a similar density. • The u -PIA shows great thermal insulation properties in anisotropic. Polyimide aerogels (PIAs) are the new type of high-performance lightweight material that combines the excellent thermal and mechanical behavior of polyimides with the highly porous and lightweight properties of aerogels. PIAs can meet the increasing material requirements of high-tech fields such as the aerospace and transportation industries. This study reports a series of all-aromatic anisotropic polyimide aerogels (p-phenylenediamine (PDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA)) with unprecedented behavior. These PIAs were synthesized using a random or unidirectional freeze-drying method followed by thermal imidization of the precursor solution. Their mechanical and thermal conductivity performance were anisotropic (u -PIA-8 strength: 1.86 and 0.14 MPa, thermal conductivity: 62.9 and 50.1 mW·m−1·K−1 along the axial and radial direction, respectively). Furthermore, the PIAs possessed excellent compression behavior in a wide temperature range from 25 °C to 316 °C, with a compressive strength over twice that of the commercial polyimide foam TEEK-HH (u -PIA-6 strength: 0.83 and 0.32 MPa at 177 and 316 °C, TEEK-HH strength: 0.31 MPa at 177 °C). These aerogels also demonstrated good thermal insulation performance after being held at 300 °C for 20 min (u -PIA-8: 76.3 °C at 25 mm). These highly anisotropic aerogels exhibit flexible thermal protection properties that extend the potential use of PIAs to applications such as high-temperature-resistant rocket fairings, sandwich structures, and arc-shaped structures for aerobats or the automobile industry. [ABSTRACT FROM AUTHOR]

The highly thermally conductive yet electrically insulating polymeric materials are exhibiting tremendous potential for thermal management materials. However, the practical application of these materials is restrained by the limited thermal conductivity (TC) and deterioration of mechanical properties. In this work, an ultraflexible polyamide-imide (PAI) film with a sandwich-like structure composed with assembled well-oriented functionalized boron nitride nanosheets (FBN) by facile layer-by-layer solution-coating strategy is constructed. The design of the layered structure and highly oriented arrangement of interconnected FBN (Herman's orientation parameter ƒ up to 0.847) endows the obtained PAI composite film with super-flexibility, ultrahigh in-plane thermal conductivity (λ //), superior thermal transfer capability (ΔT max = 24.4 °C) and excellent electrical insulation performance. The PBP composite film reaches an ultrahigh λ // of 45.7 W m−1 K−1 with only 23 wt% FBN loading and exhibits a remarkable TC enhancement factor over 23 because of the more continuous phonon transfer networks that constructed by interconnected well-oriented FBN which could effectively suppress the phonon scattering. Furthermore, the mechanical properties of the layered composite film (PB4P) exhibit noteworthy enhancement compared with uniform PBN composite film, in which the tensile strength is increased by 110% and toughness enhancement is 329%. Meaningfully, our fabrication strategy has the advantage of simplicity and adaptability for commercial amplification. The composite film developed in this work provides a promising prospect for the thermal management system of modern power electronic devices. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of eco-friendly thermal insulation material composed of recyclable wastes contributes to enhancing environmental sustainability with less pollution. In this study, polysaccharide-based aerogels with improved thermal insulation property were obtained by using konjac glucomannan, starch, and office waste paper cellulose fiber (WPCF) via sol-gel and freeze-drying method. The obtained aerogels had a bulk density of 30.1–44.9 mg/cm3, a porosity of 95.1–97.0%. Results revealed that increased WPCF addition did not impact the thermal stability, but improved the sol stability, reduced the pore size, strengthened the mechanical property, and lowered the hygroscopicity of the aerogels, benefiting practical application. Although WPCF solids showed a high thermal conductivity, increased WPCF addition at 0.1–0.5 wt% reduced the aerogel thermal conductivity, which was explained by the longer heat path and less heat convention. Further higher WPCF addition at 0.5–1.5 wt% increased the aerogel thermal conductivity as the heat conduction of solid matrix was increased and the heat convection was strengthened. Therefore, the lowest thermal conductivity (0.0335 Wm−1 K−1) of the aerogel was reached at the optimized WPCF addition of 0.5 wt%. This work showed the high potential of the WPCF to be used to strengthen the thermal insulation property of polysaccharide-based aerogels. • Fully bio-based aerogel was prepared with recyclable cellulose fiber addition. • WPCF addition changed the aerogel structure including pore shape and pore size. • The optimum thermal insulation property was achieved at WPCF addition of 0.5 wt%. • The thermal insulation mechanism was interpreted through the pore structure changes. [ABSTRACT FROM AUTHOR]

• Raw and treated doum fibers were used to produce compressed earth brick (CEB). • The mechanical and thermophysical properties of CEB are investigated. • The reinforcement by doum fibers decreases density and increases water absorption. • The addition of fibers decreases thermal conductivity and compressive strength. • The use of doum fibers promises the production of an ecological building material. This work investigates the physical and mechanical properties of compressed earth brick (CEB) reinforced with raw doum fibers (RDF) and treated doum fibers (TDF). Firstly, the raw materials were characterized. Then CEB reinforced by fibers varying from 0 to 2% by mass were elaborated. The addition of RDF and TDF reduces the compressive strength by 25% and 35% respectively. However, the inclusion of fibers improves the thermal insulation of CEB and decreases its density of about 16%. The research finding indicates also that the capillarity absorption increases with the increase of fiber content. These results indicated that the use of doum fibers to produce ecological building materials has a promising future. [ABSTRACT FROM AUTHOR]

Thermal insulation materials play an important role in energy conservation and the sustainable development of natural resources. Herein, novel silica composite nanofibers (SiO 2 NFs) with closed cell structure and excellent thermal insulation performance were designed and prepared via electrospinning technique using hollow SiO 2 /TiO 2 spheres (HSTSs) as pore-forming agent and infrared shielding agent. The addition of HSTSs broke the continuity of heat transfer pathways inside the NFs and enhanced the infrared thermal radiation shielding performance of SiO 2 NFs, endowed it with ultra-low thermal conductivity and low infrared transmittance. Meanwhile, the materials exhibited good flexibility, high tensile strength, low density and excellent thermal stability, indicating promising application as insulation materials. This research not only provides a novel strategy to prepare porous nanocomposite fibers for thermal insulation, but also offers a new insight for the development of porous materials with multiple functions. [Display omitted] • A novel strategy for constructing porous thermal insulators is reported. • Hollow SiO 2 /TiO 2 spheres broke the heat transfer pathways of the fiber and enhanced its infrared shielding performance. • The obtained SiO 2 composite nanofibers show great potential as thermal insulators in high-temperature. [ABSTRACT FROM AUTHOR]

• We develop a slim double-skin window with a 20-mm-thick air cavity and single frame. • Heating and cooling energy use was analyzed through a 15-month testbed experiment. • The proposed window exhibits comparable energy efficiency to double-skin façades. • The life-cycle costs are 47% lower than those of double-skin façades. We developed a slim double-skin window (SDSW) with the aim of reducing building energy consumption for cooling and heating, thereby reducing the impact of buildings on climate change. The developed SDSW is a slim structure with an air cavity thickness of 20 mm, i.e., thinner than that of a traditional double-skin façade (DSF). We analyzed changes in the thermal properties and cooling and heating energy consumption of the SDSW as well as the effects of the thin air cavity on window performance. A testbed was constructed to analyze the seasonal temperature properties of the glass and the cooling and heating energy consumption. We also compared the long-term effects of the air cavity on the difference between outdoor and indoor glass surface temperatures under similar conditions for the SDSW and traditional DSF. The SDSW temperature was 3 °C lower than that of the traditional DSF, and the cooling and heating energy consumption dropped by 6.5%. Although the performance of the developed SDSW was comparable to that of traditional DSF, the life-cycle cost was reduced by 47%. [ABSTRACT FROM AUTHOR]

In this paper, large-sized covalent organic framework (COF) aerogels were prepared using high-efficiency catalysis under room temperature combined with rapid gel and freeze-drying methods for the first time. Two kinds of COF aerogels with rigid and semi-rigid building blocks were prepared using this method, having good mechanical strength (126 and 106 kPa), elasticity (aerogels structure remains intact after 10 cycles), thermal insulation properties (low thermal conductivity of 0.03 wm−1K−1), low dielectric constant (1 kHz of 1.21 and 1.51), thermal stability and solvent stability, and ultra-light characteristics (densities of 0.029 and 0.040 g cm−3). Compared to the traditional COF methods that generally result in small particles, the high-efficiency catalysis method developed in this paper can be used to prepare large-sized COF aerogels under mild reaction temperatures and within less time conducive to industrial production. This method is expected to greatly broaden the application field and application scope of COF materials. [Display omitted] • Two COF aerogels were prepared combined with rapid gel and freeze-drying methods for the first time. • The COF aerogels behave good mechanical properties, thermal insulation properties, and ultra-light characteristics. • The method in this paper can be used to prepare large-sized COF aerogels under mild reaction temperatures and less time. [ABSTRACT FROM AUTHOR]

Fe-based amorphous and nanocrystalline alloys offer application prospects in the field of coating materials, and their thermal transport property is crucial for their application in thermal insulation coating. However, the mechanism of thermal conductivity in the process of isothermal annealing preparation of Fe-based nanocrystalline alloys are still unclear. In this work, the thermal conductivity of Fe 76 Si 13 B 8 Nb 2 Cu 1 amorphous alloy isochronal annealed at different temperature was examined. It was found that the thermal conductivity of the amorphous alloy is as low as 7.06 W/mK, whereas significantly increases to 10.38 W/mK after annealing at 693 K for 1800s. The result of the limited increase in thermal conductivity at annealing temperatures below the 693 K can be ascribed to the conflicting variations of electronic and phonon contributions with increasing temperature. At annealing temperature above 693 K, the two contributors start to cooperate, leading to abrupt enhancement of thermal conductivity. This work provides an insight into the thermal transport mechanisms for amorphous alloys. [ABSTRACT FROM AUTHOR]

• WMGFs were successfully prepared via chemical foaming method. • Wollastonite significantly improved mechanical strength of geopolymer foams. • WMGFs exhibited effective thermal insulation under high temperature exposure. This paper aims to investigate the physical properties and fire resistance of wollastonite-metakaolin-based geopolymer foams (WMGFs). Both compressive and flexure strengths of WMGFs are significantly improved since wollastonite fibers possess inherent stiffness and provide effective crack control. Meanwhile, wollastonite addition promotes viscosity of geopolymer slurry to some extent and then determines pores formation in foaming process, which is also crucial for mechanical strength development. The thermal conductivity of the specimens rises triflingly with elevated wollastonite addition corresponding to slightly decrease in porosity. Owing to the steady skeleton structure of WMGFs, the highest reverse-side temperature of sliced blocks is merely 202.7 °C after exposed to fire for 3 h, showing that the reduction in thermal conductivity has no negative impact on fire resistance of specimens. Physicochemical stability of wollastonite under high temperature and alkaline environment is confirmed to be vital for sustaining integrated porous skeleton structure of geopolymer foams. Therefore, geopolymer foams reinforced by wollastonite possess extraordinary mechanical strength and fire resistance, revealing strong possibility for fire protection. [ABSTRACT FROM AUTHOR]

• Layered samples of thermal mortars have lower A w than standard prism samples. • The s d of paints can depend on the substrate (singular mortar VS composite sample). • Recommended in technical sheets: s d of complete systems, and also A w for external ones. • Thermal mortars with cork/EPS: lower λ than declared, still of interest in temperate climates. • Thermal mortars: strong dependency of λ on water content. Among thermal insulation solutions for historic walls, thermal renders and plasters appear to be a very feasible option. Thus, this work analyses commercially available thermal mortars suitable for the scope. An extensive experimental campaign showed that testing single materials only, which is the standard requirement for thermal mortar-based systems, is in fact not sufficient for understanding the potential impact of the intervention on walls: whole-systems should also be examined. This study provides a detailedcharacterization of materials and systems, useful as a database for forthcoming investigations on compatibility and efficacy for application on historic walls, via numerical hygrothermal simulations. [ABSTRACT FROM AUTHOR]

Lightweight and multiscale nanocomposites are considered to be the most promising materials applied in the field of advanced aerospace and modern building industry, owing to their outstanding mechanical, thermal and flame-resistant properties served in high-temperature oxidizing environments. Herein, a novel siliconoxycarbide (SiOC) modified needle quartz fiber felt reinforced phenolic resin nanocomposite (SiQF/PR) with a hierarchical macro-/micro-/nano-scaled structure is reported. The as-prepared highly porous SiQF/PR nanocomposite exhibits a multiscale three-dimensional network and the micro-sized SiOC particles, derived from the hydrolysis of methyltrimethoxysilane (MTMS) and dimethyldiethoxysilane (DDS), are uniformly incorporated into the phenolic aerogel. The resultant nanocomposite has a bulk density of 0.30–0.35 g/cm3, and the maximum compressive strength reaches 4.20 MPa and 3.34 MPa in xy and z directions, respectively. Thermal stability and oxidation resistance experiments show that the SiQF/PR multiscale composite has a good ablation and heat insulation performance under oxyacetylene test condition, and the backside temperature of SiQF/PR is only 55.5 °C under 1.8mw/m2 for 120 s, and line ablation rate of SiQF/PR multiscale nanocomposite decreases by 20.1% at 1.8 MW/m2 and 59.5% at 0.4 MW/m2 compared to non-SiOC modified composite. These results indicate that the lightweight SiQF/PR nanocomposite fabricated by this method is very suitable for architectural or aerospace applications as high-performance insulation material. [Display omitted] [ABSTRACT FROM AUTHOR]

Polyimide (PI) foams possess excellent mechanical properties, high-temperature resistance, and other unique properties, which facilitate impact in aerospace, automotive, and microelectronics industries. However, when they are used as lightweight insulation structural layers for high-temperature carbon fiber reinforced composites, improvement in thermal-insulating properties and temperature resistance of PI foams without compromising the flexibility in extreme environments is a challenging task. In this study, the flexible blocks were linked into rigid polymeric structures to fabricate a thermoplastic structure through a simple aqueous strategy to construct hydrogen-bonding networks. Thus, with a low shrinkage of 8.42%, an ultrahigh compressive modulus of 11.17 MPa, and a specific modulus of 81.03 MPa cm3 g−1 was successfully achieved. Benefitting from the formation of ultra-strong network backbones, foams showed excellent thermal-insulating properties and temperature resistance. The robust porous material with thermal-insulating properties (0.0481 W m−1 K−1) exhibited a compression modulus of 4.21 MPa after heat treatment at 300 °C and maintained 91% strength retention, thus it can be used as lightweight heat-insulation composite sandwich structures up to 300 °C. The copolymer foam obtained by using 30 mol% flexible blocks reserves its high flexibility undergoing only 10% dimensional changes after 40,000 compression-release cycles. The lightweight thermoplastic PI foams with flexibility, thermal-insulating properties, and temperature resistance can be used for high-temperature lightweight composite sandwich structures in aeronautics and space exploration. Preparing flexible thermoplastic polyimide foams with exceptional mechanical, thermal insulating properties, and temperature resistance through a simple aqueous strategy. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Used thin profiled steel cladding as a lightweight cladding replacement for combustible ACPs in LSF buildings. • Standard fire tests of two external LSF walls showed significant fire resistance improvement due to steel cladding. • Conducted accompanying thermal property tests of two types of Earthwool insulation (glass fibre). • Evaluated total R -values of external LSF walls using THERM to understand the implication of insulation location. • Replacing cavity insulation with external insulation enhanced both fire and energy performance. This paper presents the details of full-scale standard fire tests of external light-gauge steel-framed (LSF) walls with corrugated steel cladding exposed to fire on the external side. Corrugated steel cladding of 0.42 mm thickness is generally used in roof and wall systems of buildings. In this study, it is used as the wall cladding of external LSF walls and as a lightweight cladding replacement to the combustible aluminium composite panels. A detailed investigation was undertaken to evaluate and understand the fire and energy performance of corrugated steel clad external LSF walls, which included (a) thermal property tests of two different types of Earthwool insulation (glass fibre insulation) used in wall systems, (b) full-scale (3 m × 3 m) load bearing standard fire tests of two external LSF wall systems – first with cavity insulation and the second with external insulation and (c) THERM modelling of the tested walls. Steel cladding prevented direct exposure of fire on plasterboards and hence delayed the temperature rise and increased the failure time. Overlaps along the vertical edges of steel cladding played a critical role as gaps formed during the tests. The two external LSF wall systems achieved fire resistance levels (FRLs) in excess of two hours (122 min and 158 min) with improvements greater than 40% due to the addition of thin steel cladding. Replacing cavity insulation with external insulation improved the FRL by about 30% and also its effectiveness in terms of energy efficiency. [ABSTRACT FROM AUTHOR]

Low density, high strength, together with good thermal insulation are desirable but hard to achieve simultaneously for lightweight cementitious composites. This work addresses the preparation of a novel lightweight cementitious composite (HP-LWCC) by employing the hot-pressing method and optimizing the insulating particles packing. The main raw materials are glass microspheres (GB), fly ash cenospheres (FAC), white Portland cement (PW), aluminum cement (AC), and silica fume (SF). Results showed that HP-LWCC specimens with density of 800–1200 kg/m3 exhibited superior mechanical properties and thermal insulation. Their flexural strength, compressive strength, and thermal conductivity achieved 7.5–10 MPa, 30–51 MPa, and 0.16–0.29 W/(mK), respectively. The microstructure results show that the packing of glass microspheres, which are tightly bridged by the hydration products, significantly refines the pore morphology, forming a denser cementitious matrix. The hot-pressing method benefits the reaction of aluminum cement and the alignment of fibers, resulting in high strength and flexural toughness. Based on the Compressible Packing Model, it is found that the optimized particles packing of HP-LWCC can decrease the porosity of specimens and improve the strength. Such HP-LWCC material provides a potentially solution in developing thermal insulated construction applications. [ABSTRACT FROM AUTHOR]

Owing to the rapid development of advanced power system and modern micro-electronic devices, exploiting composites with excellent thermal conductivity and dielectric properties has become increasingly important. In this work, a double-layer surface modification method of grafting dopamine (DA) at the end of 3-glycidoxypropyl-trimethoxysilane (KH560) is firstly proposed to modify the surface of boron nitride nanosheet (BNNS), for improving the thermal conductivity and dielectric properties of epoxy resin (EP). Besides, the thermal conductivity of EP composites with double-layer surface-modified BNNSs and its improvement mechanism is explored with molecular dynamics (MD) simulation from micro level. The results illustrate that thermal conductivity of EP composites doped with double-layer modified BNNSs by grafting DA at the end of KH560 (DKBP) is 0.252 W/(m·K), 129% higher than EP. Moreover, this double-layer surface modification method of DKBP is beneficial to enhance the heat transfer effect and reduce scattering effect at the interface, which is the essential reasons for improving thermal conductivity of composites. Meanwhile, DKBP composite also presents superior dielectric properties. This work provides a promising idea to develop new insulating materials with high thermal conductivity. [Display omitted] • Grafting DA at the end of KH560 is firstly proposed to functionalize BNNSs. • Thermal conductivity and electrical properties of DKBP are enhanced significantly. • Improvement mechanism is explored by molecular dynamics simulation. • This method improves transfer effect and reduces scattering effect at the interface. [ABSTRACT FROM AUTHOR]

In order to study the effect of zirconia on the properties of laser deposited Ni15 coating on Q345 steel, laser deposition experiments were carried out with LSJG-GQ-6000M3 laser equipment with rated power of 6000 watts. The effects of adding zirconia on the microstructure, wear resistance and thermal insulation of the coating were studied by electron microscope, energy dispersive spectrometer, hardness tester, friction and wear tester and thermocouple. Study found that the addition of zirconia can refine the microstructure, improve the hardness and reduce the friction coefficient. The wear pattern has changed, and the high temperature resistance of the coating is improved. [ABSTRACT FROM AUTHOR]

Biomass-derived aerogels have received extensive attention as potential thermal management materials for energy-efficient buildings. However, it remains a huge challenge to fabricate a fully bio-based aerogel with excellent mechanical property, flame retardancy, and low thermal conductivity. Herein, we demonstrate a novel and facile strategy to manufacture a fully biomass-based aerogel from naturally abundant ammonium alginate (AL) and phytic acid (PA), in which PA acting as both flame retardant and cross-linking components constructs a strong network with AL matrix. Consequently, the resultant biomass aerogel with a low density of 0.052 g/cm3 exhibits ultrahigh mechanical modulus (25.1 ± 3.1 MPa) and specific modulus (440.4 ± 54.4 MPa cm3·g−1), much superior to those of biomass aerogels ever reported. Due to the existence of the uniform three-dimensional porous network, the biomass aerogels exhibit low thermal conductivity (34–38 mW/m·K) and excellent thermal insulation performances. Further, the introduction of PA endows the aerogel with high flame retardancy (limiting oxygen index value of 57%, UL-94 V-0 rating, and extremely low heat release), while the biodegradability of the materials keeps at a high level with a biodegradation rate of 91.43%. Combining with the advantages of mechanically strong property, high flame retardancy, excellent thermal insulation, and biodegradation, the aerogel of this work provides a new strategy to fabricate thermal insulation materials with high environmental safety. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel high-entropy oxide (YYHEO) was engineered with significant mass disorder. • YYHEO exhibited glass-like low thermal conductivity (1.27 W/m∙K). • YYHEO exceeded typical substitutional solid solubility limit even with a significant atomic size difference (>50%). • YYHEO shows thermal stability even at elevated temperature (1500 ° C) without any phase degradation. • Thermophysical properties were compatible with YSZ (CTE: 10.08 × 10−6 K−1, E : 218.21 ± 3.64 GPa and H : 14.42 ± 0.5 GPa). An entropy-stabilization strategy was applied to engineer a novel thermal insulating material by establishing a single-phase solid solution with the formula of (Y 1/2 Yb 1/2) 2 (Ti 1/3 Zr 1/3 Hf 1/3) 2 O 7 (YYHEO). Structural analysis revealed that this material exceeded the typical substitutional solubility limit, even with a significant atomic size difference, where the conventional determination rule was defied. YYHEO exhibited a lower glass-like thermal conductivity due to its highly disordered crystal structure and the specific design strategy. The coefficient of thermal expansion and mechanical properties (e.g. elastic modulus and hardness) were comparable to conventional materials, suggesting that YYHEO is a promising candidate for application as a new thermal insulating material. [ABSTRACT FROM AUTHOR]

• Lignocellulosic bio-wastes from forest management and agro-industry as building materials are reviewed. • Some bio-wastes produced in Euro-Mediterranean countries are selected. • Studies on eco-efficient boards made of natural fibers and other bio-wastes are analysed. • Further studies on properties of bio-wastes and eco-efficient boards are needed. This study investigates the possibility of using agro-industrial wastes for building products, mainly focusing on their insulation properties. A classification of bio-wastes is provided, namely of the lignocellulosic ones and their features and properties are described. Information about three main topics is collected: world production and consumption of some crops already used as building materials, their chemical composition and their most studied properties. Since the considered materials are lignocellulosic and they have many common features, a comparison is made. The aim is to have comparable information to support future research related to the production of eco-efficient indoor insulation boards. The result of this research is the choice of four different agro-industrial wastes produced in the Euro-Mediterranean Countries. This area was chosen as buildings typically have little or no insulation due to the regional mild climate; however, particularly with climate change, indoor hygrothermal comfort is poor. The collection of information allows some conclusions to be reached about the different bio-wastes already studied and identify gaps in the literature. [ABSTRACT FROM AUTHOR]

The microstructure of thermal spray powders plays a significant role in the application performance of thermal protection coatings deposited by air plasma spraying. Based on the design of the spray powder structure, the YSZ@Cu core-shell structure powders have the potential to be a thermal conduction anisotropy material for thermal protection coating, owing to the special alternate-layered structure formed during plasma spraying. To study the mechanism of the thermal conduction anisotropy of YSZ/Cu composite coatings, the YSZ coatings, YSZ@Cu coatings and YSZ-Cu coatings were fabricated by YSZ powders, YSZ@Cu core-shell structure powders and YSZ-Cu mechanical mixture powders, respectively. There were YSZ vertical thermal insulation layer and Cu horizontal thermal condition layer in the YSZ@Cu coatings, which provides a structural basis for the realization of thermal conduction anisotropy. Compared with the YSZ-Cu coatings, the temperature difference between the back-surface center area and the edge area of the YSZ@Cu coatings is significantly reduced by approximately 37%, which is attributed to the synergistic effect of alternate-layered comprising the YSZ layer and the high thermal conductivity Cu layer. YSZ@Cu coatings can effectively prevent the rapid rise in local temperature by the analysis of finite-element simulation, which is beneficial for prolonging the service life of the thermal protection coating in a non-uniform temperature field. • To reveal thermal conduction anisotropy, YSZ@Cu core-shell structure powder was used to fabricate composite coatings by APS. • The YSZ@Cu coating has an alternate-layered structure including horizontal thermal conduction and vertical thermal isolation layer. • Based on experimental analysis, the novel YSZ@Cu coating make surface temperature difference reduce by approximately 37%. [ABSTRACT FROM AUTHOR]

Advanced composite aerogel materials have attracted much attention due to the unique structure and properties. However, the efficient manufacturing process and structural stability were still a challenge. Herein, a novel hydroxyapatite nanowires/polyimide (HAnws/PI) composite aerogel was synthesized by the ultralong HAnws combined with polyamic acid via directional freezing and thermal imidization. Among them, the HAnws and PI intertwined to form a three-dimensional network structure, which decreased the volume shrinkage of aerogel in thermal imidization from 42.9% to 12.6%, resulting in high porosity (>96%) and low density (0.0329–0.0431 g cm−3). In addition, the HAnws/PI aerogel with layered porous structure exhibits obvious anisotropic mechanical properties. The axial specific modulus as high as 78.05 kN m kg−1 and radial high elasticity can withstand 100 cycles of fatigue resistance. Moreover, the lowest radial thermal conductivity at 32.21 mW m−1 K−1 and the maximum of the anisotropy factor was 2.2, which was very suitable for insulation pipes to prevent additional heat loss. Therefore, the novel nanofibers reinforced organic aerogel was expected to provide more abundant functional applications in energy efficiency. [Display omitted] • HAnws can effectively inhibit the volume shrinkage of HAnws/PI aerogel. • The composite aerogel with tubular pores was prepared by directional freezing. • HAnws/PI aerogel exhibited anisotropic mechanical properties and thermal insulation. • HAnws/PI aerogel showed a low radial thermal conductivity and the maximum of the anisotropy factor was 2.2. [ABSTRACT FROM AUTHOR]

The combination of room-temperature phase change materials (PCMs) and building materials can reduce the energy consumption of heating equipment and improve indoor thermal comfort. In this paper, the novel CaCl 2 ·6H 2 O–CO(NH 2) 2 /SiO 2 room-temperature shape-stable composite PCM was fabricated by melt-blending method with CaCl 2 ·6H 2 O as the basic PCM, CO(NH 2) 2 as the phase change temperature regulator and hydrophilic fumed silica (SiO 2) as the carrier. The temperature-regulating effect of CO(NH 2) 2 on CaCl 2 ·6H 2 O and the shape-stabilizing effect of SiO 2 on CaCl 2 ·6H 2 O–CO(NH 2) 2 PCM were emphatically analyzed. The results revealed that the obtained composite PCM with 6% CO(NH 2) 2 and 20% SiO 2 possessed a favorable form-stability, relatively high enthalpy (114.3 J g-1) and appropriate phase change temperature (21.03 °C) which decreased by 7.81 °C compared with pure CaCl 2 ·6H 2 O (28.84 °C). Furthermore, its small supercooling degree (0.259 °C), low thermal conductivity (0.3667 W·m-1·K-1) as well as the excellent cyclic reliability and thermal stability indicated that the composite PCM has good thermodynamic properties, enabling its application for indoor building thermal insulation and even some other areas. • The PCT of calcium chloride hexahydrate can be reduced by urea. • By adding SiO 2 , the PCM is shape-stabilized and its PCT is further adjusted. • The CPCM reveals high latent heat and low thermal conductivity. • The CPCM exhibits excellent thermal stability. [ABSTRACT FROM AUTHOR]

Cellulose which is the most abundant and renewable biopolymer is drawing a tremendous level of attention, that will continue to grow in the future driven by the sustainability trend. In this study, cellulose was extracted and functionalized using a chemical modification and blended with metallic nanoparticles such as zinc oxide (ZnO-NPs) and copper oxide (CuO-NPs) that take a growing interest related to their unsurpassed quintessential physical and chemical properties. SEM results indicate that the metallic nanoparticles were highly prepared and attached to the surface of the modified cellulose (MC). FTIR confirmed the successful functionalization of cellulose, while XRD results showed the characteristic diffraction peaks of ZnO and CuO nanoparticles. DSC reveals that the thermal stability of the modified cellulose increased with the addition of CuO-NPs and ZnO-NPs. The TGA/DTA analysis evaluates the thermal degradation of all cellulosic materials and affirms higher stability of Zn-NPs/MC compared to MC and CuO-NPs/MC. The heat insulation performances were evaluated using a heat insulation device constructed at our laboratory, which exhibits the highest insulation of ZnO-NPs/MC than CuO-NPs/MC. • Hybrid films based on modified cellulose and oxide nanoparticles using in situ method were prepared. • The addition of metallic oxide nanoparticles changes the heat conductivity of the matrix-based cellulose. • ZnO-NPs/MC material exhibits higher stability than CuO-NPs/MC. [ABSTRACT FROM AUTHOR]

• Poor solvents were introduced into the reagent during the synthesis of PI precursor. • Submicron-scale pores are produced in aerogels owing to the poor solvents. • Aerogels in this work have low density (~91 mg cm−3) and low thermal conductivity. The sol–gel process is essentially a process of phase separation between micelles and solvent, so the influence of solvent composition on the result of phase separation will further affect the wet gel and the structure of the aerogel made by it. In this study, during the preparation of polyimide (PI) aerogels, poor solvents were introduced into the reagent during the synthesis of PI aerogel precursor, polyamic acids. The pore structure and thermal insulation performance changes of the PI aerogels caused by this behavior were studied. With the addition of poor solvent, submicron-scale pores were found inside the aerogel. In addition, the introduction of a small amount of poor solvent improved the thermal insulation performance of the prepared PI aerogel. [ABSTRACT FROM AUTHOR]

Excellent thermal insulating aerogels have broad application prospects in pipeline transportation, aerospace, construction and other fields. However, defects in thermal stability and mechanical are the main factors limiting their use to special environments. In this work, a novel polyimide composite aerogel is successfully synthesized through 3-Aminopropyltriethoxysilane (APTES) functionalized clay halloysite nanotubes (FHal) as inorganic enhancement phase and uniformly embedded in polyimide (PI) aerogels. Functionalization can increase the interfacial compatibility between clay inorganic phase and polyimide acid. The results indicated that FHal with high aspect ratio interacts with PI to form a three-dimensional network structure. The FHal/PI composite aerogels had low shrinkage (21.9%–30.79%), low bulk densities (65.285–71.464 mg/cm3), low thermal conductivities (39.18–42.57 mW/(m·K)), high thermal stability (onset of decomposition above 520 °C) and excellent mechanical property (1.14 MPa, 2.62 times of pure PI aerogel). Therefore, FHal/PI composite aerogels can be used as a promising thermal management material for practical and complex insulation applications. [Display omitted] • Hal can effectively inhibit the shrinkage of PI aerogel during preparation. • The functional process enhances the interaction between Hal and PI. • FHal/PI aerogels have excellent thermal insulation and mechanical properties. [ABSTRACT FROM AUTHOR]

New organic-inorganic polyurethane-based hybrids with enhanced mechanical properties and thermal insulation properties are reported. Polyurethane-based hybrids are characterized by the intimate interactions of their inorganic and organic co-networks and prepared by sol-gel approach, have exhibited properties exceeding those of polyurethane foams, e.g. enhanced thermal stability, durability and thermal insulating effectiveness. However, mechanical properties have previously been poor. Here, new porous organic-inorganic materials consisting of a polyurethane network modified by in-situ formation of aerogel-like polysiloxane domains, were developed. They exhibit a multiscale-porosity which enhances the insulation, mechanical and thermal properties. The synthesis was performed through a novel stepwise process consisting of: preparation of a siloxane precursor based on methyl-triethoxysilane and tetraethoxysilane; functionalization of traditional polyol for polyurethane foams with 3-(triethoxysilanepropyl)isocyanate as coupling agent; use of suitable catalysts and silicone surfactants; and foaming with methylene-di-isocyanate compound. The siloxane precursors and coupling agent led to formation of "aerogel-like" polysiloxane domains within the walls and struts of the polyurethane foams. The synthesis method enabled increased incorporation of the "aerogel-like" polysiloxane structures into the foams, compared to literature, with 20 wt% SiO 2 , reducing thermal conductivity of the hybrid foams 30% compared with pristine polyurethane, in addition to significant improvement in thermal stability and mechanical properties. [Display omitted] [ABSTRACT FROM AUTHOR]

To reduce energy losses due to the insufficient thermal insulation is one of the current "hot" topics. Various commercial porous materials are used with the best conductivity around 0.03–0.04 W/(m·K). Aerogels are the only known materials with "intrinsic" thermal superinsulating properties, i.e. with thermal conductivity below that of air in ambient conditions (0.025 W/(m·K)). The classical thermal superinsulating aerogels are based on silica and some synthetic polymers, with conductivity 0.014–0.018 W/(m·K). Aerogels based on natural polymers are new materials created at the beginning of the 21st century. Can bio-aerogels possess thermal superinsulating properties? What are the bottlenecks in the development of bio-aerogels as new high-performance thermal insulationing materials? We try to answer these questions by analyzing thermal conductivity of bio-aerogels reported in literature. • Thermal conductivity of bio-aerogels is analysed. • Correlations between thermal conductivity and aerogel density and surface area are built. • A special focus is made on thermal conductivity below that of air. • Prospects of using bio-aerogels for thermal insulation are discussed. [ABSTRACT FROM AUTHOR]

The phonon density of states and thermal conductivity of La 2 Zr 2 O 7 and Gd 2 Zr 2 O 7 are tuned to get materials with improved thermal insulation properties. In this study, pure and doped models of La 2 Zr 2 O 7 and Gd 2 Zr 2 O 7 were developed and simulated based on density functional theory. Doping Gd at La sites in La 2 Zr 2 O 7 was observed to modify the band structure. The density of states analysis showed that Gd d states were introduced in the band gap. With increasing Gd concentration, the band gap of La 2 Zr 2 O 7 was initially populated and then, a clear band gap was observed at high Gd/La ratios. Smoothness in the phonon density of states curves was observed with an increase in Gd concentration. However, irregular phonon density of states curves was obtained for the Gd 2 Zr 2 O 7 system. Among the simulated models, the La 16-5 Gd 5 Zr 16 O 56 system with Gd/La ratio of 0.454 provided minimum thermal conductivity. [ABSTRACT FROM AUTHOR]