Size-structure-property relationship of wood particles in aqueous and dry insulative foams

Three size-fractionated samples of pine beetle-killed wood particles were used to prepare lightweight insulative foams. The foams were produced by foam-forming an aqueous slurry containing wood particles (125-1000 μm), a polymer binder, and surfactant, followed by oven drying. The effect of wood particle size on the aqueous foam stability, structure, and performance of insulative foams was investigated. While all aqueous foams were highly stable, aqueous foam stability increased with decreasing particle size. For dry foams, the cell size distribution was similar for all particle sizes as it was primarily controlled by the surfactant; differences occurred within the cell wall structure. A size-structure-property relationship was identified using x-ray micro-computed tomography where smaller particles produced lighter cell wall frameworks, leading to lower densities and decreased thermal conductivity and compressive strength. Larger particles produced denser cell wall frameworks that were more resistant to deformation, although all dry foams had sufficient mechanical properties for use as insulation panels. Thermal conductivity for all wood particle size-fractionated samples was <0.047 W m-1 K-1 making the foams similar to expanded polystyrene/polyurethane and supporting their use as thermal insulation in buildings.

Mechanically robust, thermal insulating sustainable foams fully derived from bamboo fibers through high temperature drying

The development of lignocellulosic foams has been gaining momentum due to their sustainability and biodegradability. However, lignocellulosic foams often have low preparation efficiency and poor mechanical properties, especially compression performance. Here, we constructed mechanically robust and thermal insulating cellulosic foams through high-temperature drying, in which all bamboo-sourced lignin-containing pulp fibers (LPF) and steam explosion fibers (SEF) were chosen as a skeleton and high solid fibrillated cellulose (HSFC) as a binder. This study aimed to investigate the effects of the characteristics of bamboo fibers and the HSFC addition on the formation, and mechanical- and thermal insulation performances of the resulting foams. The HSFC incorporation endowed the foams with excellent mechanical performance, the stress at 10 % strain and compressive modulus were 0.29 MPa and 4.4 MPa, respectively, which were 10-fold and 44-fold compared to LPF foam without HSFC. The LPF/HSFC possessed excellent energy absorption capacity (170 kJ/m3 under 40 % strain) as well as good thermal insulating performance (0.054 W/(m·K)). The LPF/HSFC foam with a much more homogeneous cellular structure outperformed the SEF/HSFC foam. This work suggests that the developed bamboo fiber foams hold promise for use in protective packaging and thermal insulation applications.

Anisotropic composite aerogel with thermal insulation and flame retardancy from cellulose nanofibers, calcium alginate and boric acid

With the increasing severity of energy shortages and environmental pollution, there is an urgent need for advanced thermal insulation materials with excellent comprehensive performance, including low thermal conductivity, high flame resistance, and strong compressive strength. Herein, an anisotropic composite aerogel based on cellulose nanofibers (CNF), calcium alginate (CA), and boric acid (BA) is fabricated using a directional freeze-drying strategy. The CA and BA, as double cross-linking agents, associated with oriented porous structure provide the resultant aerogel with good mechanical strength. Additionally, self-flame retardant CA and BA act as synergistic flame retardants that endow the aerogel with excellent flame retardance properties such as a limiting oxygen index value of 44.2 %, UL-94 V-0 rating, and low heat release. Furthermore, this composite aerogel exhibits outstanding thermal insulation performance with a low thermal conductivity of approximately 30 mW m-1 K-1. Therefore, the composite aerogel is expected to have a wide potential application in areas such as construction, automotive industry, batteries, petrochemical pipelines, and high-temperature reaction devices.

Eco-friendly bamboo pulp foam enabled by chitosan and phytic acid interfacial assembly of halloysite nanotubes: Toward flame retardancy, thermal insulation, and sound absorption

Lightweight, porous cellulose foam is an attractive alternative to traditional petroleum-based products, but the intrinsic flammability impedes its use in construction. Herein, an environmentally friendly strategy for scalable fabrication of flame-retardant bamboo pulp foam (BPF) using a foam-forming technique followed by low-cost ambient drying is reported. In the process, a hierarchical structure of halloysite nanotubes (HNT) was decorated onto bamboo pulp fibers through layer-by-layer assembling of chitosan (CS) and phytic acid (PA). This modification retained the highly porous microcellular structure of the resultant BPF (92 %-98 %). It improved its compressive strength by 228.01 % at 50 % strain, endowing this foam with desired thermal insulation properties and sound absorption coefficient comparable to commercial products. More importantly, this foam possessed exceptional flame retardancy (47.05 % reduction in the total heat release and 95.24 % reduction in the total smoke production) in cone calorimetry, and it showed excellent extinguishing performance, indicating considerably enhanced fire safety. These encouraging results suggest that the flame retardant BPF has the potential to serve as a renewable and cost-effective alternative to traditional foam for applications in acoustic and thermal insulation.

Superelastic and superflexible cellulose aerogels for thermal insulation and oil/water separation

Aerogels with low thermal conductivity and high adsorption capacity present a promising solution to curb water pollution caused by organic reagents as well as mitigate heat loss. Although aerogels exhibiting good adsorption capacity and thermal insulation have been reported, materials with mechanical integrity, high flexibility and shear resistance still pose a formidable task. Here, we produced bacterial cellulose-based ultralight multifunctional hybrid aerogels by using freeze-drying followed by chemical vapor deposition silylation method. The hybrid aerogels displayed a low density of 10-15 mg/cm3, high porosity exceeding 99.1 %, low thermal conductivity (27.3-29.2 mW/m.K) and superior hydrophobicity (water contact angle>120o). They also exhibited excellent mechanical properties including superelasticity, high flexibility and shear resistance. The hybrid aerogels demonstrated high heat shielding efficiency when used as an insulating material. As a selective oil absorbent, the hybrid aerogels exhibit a maximum adsorption capacity of up to approximately 156 times its own weight and excellent recoverability. Especially, the aerogel's highly accessible porous microstructure results in an impressive flux rate of up to 162 L/h.g when used as a filter in a continuous oil-water separator to isolate n-hexane-water mixtures. This work presents a novel endeavor to create high-performance, sustainable, reusable, and adaptable multifunctional aerogels.

Highly Porous Yet Transparent Mechanically Flexible Aerogels Realizing Solar-Thermal Regulatory Cooling

The demand for highly porous yet transparent aerogels with mechanical flexibility and solar-thermal dual-regulation for energy-saving windows is significant but challenging. Herein, a delaminated aerogel film (DAF) is fabricated through filtration-induced delaminated gelation and ambient drying. The delaminated gelation process involves the assembly of fluorinated cellulose nanofiber (FCNF) at the solid-liquid interface between the filter and the filtrate during filtration, resulting in the formation of lamellar FCNF hydrogels with strong intra-plane and weak interlayer hydrogen bonding. By exchanging the solvents from water to hexane, the hydrogen bonding in the FCNF hydrogel is further enhanced, enabling the formation of the DAF with intra-layer mesopores upon ambient drying. The resulting aerogel film is lightweight and ultra-flexible, which possesses desirable properties of high visible-light transmittance (91.0%), low thermal conductivity (33 mW m-1 K-1), and high atmospheric-window emissivity (90.1%). Furthermore, the DAF exhibits reduced surface energy and exceptional hydrophobicity due to the presence of fluorine-containing groups, enhancing its durability and UV resistance. Consequently, the DAF has demonstrated its potential as solar-thermal regulatory cooling window materials capable of simultaneously providing indoor lighting, thermal insulation, and daytime radiative cooling under direct sunlight. Significantly, the enclosed space protected by the DAF exhibits a temperature reduction of 2.6 °C compared to that shielded by conventional architectural glass.

Environment-friendly, high-performance cellulose nanofiber-vanillin epoxy nanocomposite with excellent mechanical, thermal insulation and UV shielding properties

With the increased demand for biobased epoxy thermosets as an alternative to petroleum-based materials in various fields, developing environment-friendly and high-performance natural fiber-biobased epoxy nanocomposites is crucial for industrial applications. Herein, an environment-friendly nanocomposite is reported by introducing cellulose nanofiber (CNF) in situ interaction with lignin-derived vanillin epoxy (VE) monomer and 4, 4´-diaminodiphenyl methane (DDM) hardener that serves as a multifunctional platform. The CNF-VE nanocomposite is fabricated by simply dispersing the CNF suspension to the VE and DDM hardener solution through the in-situ reaction, and its mechanical properties and thermal insulation behavior, wettability, chemical resistance, and optical properties are evaluated with the CNF weight percent variation. The well-dispersed CNF-VE nanocomposite exhibited high tensile strength (∼127.78 ± 3.99 MPa) and strain-at-break (∼16.49 ± 0.61 %), haziness (∼50 %) and UV-shielding properties. The in situ loading of CNF forms covalent crosslinking with the VE and favors improving the mechanical properties along with the homogeneous dispersion of CNF. The CNF-VE nanocomposite also shows lower thermal conductivity (0.26 Wm-1K-1) than glass. The environment-friendly and high-performance nanocomposite provides multiple platforms and can be used for building materials.

Development of lightweight, high-strength, and highly porous ligno-nanocellulosic foam with excellent antioxidant and insulation properties

This study reports an environmentally friendly ligno-nanocellulosic foam prepared by utilizing lignin (LGN), cellulose nanofiber (CNF), and citric acid (CA) as a green crosslinker through an easy, low-cost, and environmentally friendly process. The FTIR study and XPS analysis of the prepared LGN/CNF foams confirm the crosslinking between the components, which leads to lower shrinkage, lower density, and higher porosity than the neat CNF foam, achieving a remarkably low density of 19.59 mg/cm3 and high porosity of 98.84 % The morphology and microstructure of the foam show a uniform three-dimensional porous network built by strong cell walls. The crosslinked LGN/CNF foams indicate 182 % higher compressive modulus and 306 % higher compressive strength at 70 % strain than the neat CNF foam. Further, the addition of LGN and CA enhances the antioxidant activity of the foam. The prepared foam shows lower thermal conductivity and better sound absorption performance than the neat CNF foam, indicating a potential to be used as thermal insulation and sound-absorbing materials that can mitigate greenhouse gas emissions.

Sustainable lignocellulose aerogel for air purifier with thermal insulation, flame retardancy, mechanical strength, and its life cycle assessment

High-performance biomass materials with good thermal insulation, flame retardrancy, and mechanical properties are urgently required for thermal management. Herein, a novel lignocellulose aerogel treated using a recyclable deep eutectic solvent (DES) was physically mixed with tourmaline particles (TPs) to enhance its structural stability, flame retardancy, and mechanical properties. The optimized TPs-modified lignocellulose aerogel (TLA-4) had good comprehensive performances due to the synergistic effect of ammonium sulfate and TPs. Compared with TPs-free lignocellulose aerogel (LA), the total heat release (THR) and heat release rate (HRR) of TLA-4 were reduced by 62.0 % and 66.3 %, respectively, and the limiting oxygen index (LOI) of TLA-4 was drastically enhanced by 74.1 %. TLA-4 also exhibited a low thermal conductivity of 29.67 mW/mK, showing favorable thermal insulation performance. When compressed to 5 %, the mechanical strength of TLA-4 increased by 8.3 times. Meanwhile, the presence of TPs and abundant pores in the aerogel contributed to the release of negative oxygen ions (NOIs), aiding air purification. A life cycle assessment (LCA) indicated that this composite had a minimal environmental impact (EI) in 17 categories compared to other similar aerogels. The proposed strategy for preparing an environment-friendly lignocellulose aerogel offers significant potential for applications in home decoration and building materials.

Exploring the Versatility of Aerogels: Broad Applications in Biomedical Engineering, Astronautics, Energy Storage, Biosensing, and Current Progress

Aerogels are unique and extremely porous substances with fascinating characteristics such as ultra-low density, extraordinary surface area, and excellent thermal insulation capabilities. Due to their exceptional features, aerogels have attracted significant interest from various fields, including energy, environment, aerospace, and biomedical engineering. This review paper presents an overview of the trailblazing research on aerogels, aiming at their preparation, characterization, and applications. Various methods of aerogel synthesis, such as sol-gel, supercritical drying, are discussed. Additionally, recent progress in the characterization of aerogel structures, including their morphology, porosity, and thermal properties, are extensively reviewed. Finally, aerogel's utilizations in numerous disciplines, for instance, energy storage, thermal insulation, catalysis, environmental remedy, and biomedical applications, are summarized. This review paper provides a comprehensive understanding of aerogels and their prospective uses in diverse fields, highlighting their unique properties for future research and development.

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.

Analysis of glove local microclimate properties for various glove types and fits using 3D scanning method

Due to their geometry and thermal physiology, hands are most vulnerable to cold weather injuries and loss of dexterity. Gloves are the most common for hand protection during exposure to extreme thermal and hazardous environments. Although glove microclimate properties such as area factor, air gap thickness, and contact area play a significant role in thermal protection, identifying local (at individual hand segments) glove microclimate properties is still a research gap. For the first time, the glove-microclimate properties for 16 hand segments at high spatial resolution were analyzed by employing state-of-the-art hand-held 3D scanner and post-processing techniques for different glove types. Our results clearly indicate that the glove area factor for distal phalanges is significantly higher (by 49.8 %) than that for other hand segments, which increases the heat transfer from distal phalanges. In contrast, average air gap thickness was relatively uniform across all hand segments. The glove type had a pronounced effect on glove microclimate properties, e.g., bulky and heavy cold weather protective gloves had a larger average air gap thickness and glove area factor. Regression models are also developed to estimate the glove microclimate properties from simple measurement (i.e., ease allowance). Overall, this study provides essential information for the design and development of protective gloves that can help improve safety, comfort, and dexterity. Methods and mathematical models developed in this study also contribute to facilitating extremity (e.g., hand) focused thermoregulation modeling, hazard simulation, injury prediction, ergonomic design, optimum performance (dexterity and tactility) along with thermal protection.

Ultrastrong lightweight nanocellulose-based composite aerogels with robust superhydrophobicity and durable thermal insulation under extremely environment

Ultra-lightweight porous aerogels based on nanocellulose (NC) have promising applications in various fields such as building insulation, sewage treatment, energy storage, and aerospace. One of the key advantages of these aerogels is their exceptionally low thermal conductivity. Nevertheless, the thermal insulation of NC aerogel (NCA) can deteriorate with changes in temperature and humidity conditions, making it crucial to develop a bulk aerogel that can maintain exceptional thermal insulating properties in harsh environmental conditions. A sustainable and user-friendly approach to synthesizing cellulose/poly(vinyl alcohol) aerogel (CellPA) materials has been developed, which are lightweight, possess good insulating properties, and demonstrate robust superhydrophobicity even in harsh environmental conditions. The CellPA are both exceptionally lightweight and robust, boasting outstanding resistance to combustion while also displaying a thermal conductivity of 36.1 mW m-1 K-1, suggesting they hold great promise for insulation applications. Furthermore, CellPA also exhibits robust superhydrophobicity even under harsh conditions, confirming the homogenous superhydrophobic modification of the biodegradable PVA through chemical methods. The manufacturing of bio-based composite materials with enhanced mechanical and thermal insulation features has gained immense popularity in a broad spectrum of contemporary engineering applications. These composite materials are particularly valuable as a robust, energy-efficient, lightweight, waterproof and flameproof for construction materials.

Guar-based aerogels with oriented lamellar structure and lightweight properties for flame-retardant and thermal insulation

In this study, a multi-functional guar gum aerogel with the oriented lamellar structure, which introduced sodium silicate (Na2O·nSiO2) and phytic acid (PA) as thermal insulation additives and flame-retardant agents, respectively, was fabricated via freeze drying. Our aerogel's chemical structure, morphology, and thermal and mechanical properties were analyzed. The oriented lamellar structure was attributed to the orientated growth of ice crystals, which was induced by the "silicate-guar, guar-phytate, and phytate-silicate" multiple hydrogen bonds formed between Na2O·nSiO2, PA, and guar gum. The density of the sample with 2 wt% PA could reach 0.0335 g·cm-3, and the porosity was 5 %, along with a specific pore volume of 0.8144 cm3·g-1. The mechanical properties and thermal insulation performed significant differences in the radial and axial direction of the oriented lamella (nearly 100 % resilience while 50 % deformation quantity and 0.0235 W/(m*K) of thermal conductivity in the radial direction, up to 0.079 MPa of compressive strength in the axial direction). The presence of PA attached a good flame-retardant ability to our aerogel (The Limiting Oxygen Index (LOI) was 30.77 %). This work provides a novel and promising method for developing anisotropic aerogel with excellent potential in building energy efficiency and flame-retardant.

Hollow glass microspheres embedded in porous network of chitosan aerogel used for thermal insulation and flame retardant materials

In recent years, biopolymer aerogels as thermal insulation materials have received widespread attention due to natural abundance, cost-efficiency, and environment-friendly. However, the flammability and low strength hinder its practical application. Hollow glass microspheres (HGMs) as an inorganic thermal insulation filler have been filled in biopolymer aerogels to improve flame retardancy. However, the structure formed by HGMs embedded porous network of biopolymer aerogel has rarely been investigated, which not only reduce thermal conductivity through high porosity, but also adjust the filling volume of HGMs and achieve uniform distribution through chemical cross-linking. Herein, a biopolymer aerogel composite was assembled by chitosan aerogel (CSA) and different volume of HGMs by chemical cross-linking, freeze-drying, and silylation modification processes. When the filling volume fraction of HGMs reached 40 %, a skeleton structure was initially formed. The composites with HGMs volume of 40 %-60 % exhibited low density, high porosity, low thermal conductivity, good mechanical property, and excellent flame retardancy. According to GB 8624-2012 standard for classification, the composite with 60 % HGMs achieved class A1 non-combustible.

Konjac glucomannan-based aerogels with excellent thermal stability and flame retardancy for thermal insulation application

Biomass aerogels are a promising kind of environment-friendly thermal insulation material. However, the flammability, poor water resistance, and thermal instability of biomass aerogels limit their applications. Herein, freeze-drying and thermal imidization were used to create konjac glucomannan (KGM), boron nitride (BN), and polyimide (PI)-based aerogels with a semi-interpenetrating network structure. The introduction of BN was beneficial to improve the mechanical properties and thermal stability of aerogels. The imidization process of PI improved the hydrophobicity, mechanical property, and flame retardancy of the aerogels. The synergistic effect of PI and BN reduced the peak heat release rate and total heat release rate of KGM-based aerogel by 55.8 % and 35 %, respectively, and endowed aerogel with good self-extinguishing performance. Moreover, the results of thermal conductivity and infrared thermal imaging demonstrated that the aerogels had excellent thermal insulation properties, and could effectively manage thermal energy over a wide range of temperatures. This study provides a simple method for the preparation of heat-insulating aerogel with high fire safety, which has broad application prospects in the field of energy saving and emission reduction.

Metal-Organic Gel Leading to Customized Magnetic-Coupling Engineering in Carbon Aerogels for Excellent Radar Stealth and Thermal Insulation Performances

Metal-organic gel (MOG) derived composites are promising multi-functional materials due to their alterable composition, identifiable chemical homogeneity, tunable shape, and porous structure. Herein, stable metal-organic hydrogels are prepared by regulating the complexation effect, solution polarity and curing speed. Meanwhile, collagen peptide is used to facilitate the fabrication of a porous aerogel with excellent physical properties as well as the homogeneous dispersion of magnetic particles during calcination. Subsequently, two kinds of heterometallic magnetic coupling systems are obtained through the application of Kirkendall effect. FeCo/nitrogen-doped carbon (NC) aerogel demonstrates an ultra-strong microwave absorption of - 85 dB at an ultra-low loading of 5%. After reducing the time taken by atom shifting, a FeCo/Fe3O4/NC aerogel containing virus-shaped particles is obtained, which achieves an ultra-broad absorption of 7.44 GHz at an ultra-thin thickness of 1.59 mm due to the coupling effect offered by dual-soft-magnetic particles. Furthermore, both aerogels show excellent thermal insulation property, and their outstanding radar stealth performances in J-20 aircraft are confirmed by computer simulation technology. The formation mechanism of MOG is also discussed along with the thermal insulation and electromagnetic wave absorption mechanism of the aerogels, which will enable the development and application of novel and lightweight stealth coatings.

Freeze-casting production of thermal insulating and fire-retardant lightweight aerogels based on nanocellulose and boron nitride

Cellulose aerogels exhibit biocompatibility and biodegradability, rendering them promising candidate for application in building energy conservation and insulation materials. However, the intrinsic inflammability of pristine cellulose aerogel causes unneglectable safety concerns, hindering their application in energy-efficient buildings. Herein, a thermal insulating, fire-retardant, strong, and lightweight aerogel was produced via freeze-casting suspensions of cellulose nanofibril (CNF) and l-glutamine functionalized boron nitride nanosheets (BNNS-g). The aerogel with a BNNS-g:CNF concentration ratio of 15:5 exhibited outstanding mechanical strength owing to the strong interaction between BNNS-g and CNF as well as satisfactory thermal insulating performance (0.052 W/m·K). Particularly, this aerogel showed excellent fire-retardant and self-extinguishing capabilities in the vertical burning test, which remained unscathed after over 60 s of burning in a butane flame. Further, the limit oxygen index (LOI) of this aerogel was 36.0 %, which was better than the LOIs of traditional petrochemical-based insulating materials. This study provides a promising strategy for producing aerogels with excellent properties using cellulose and other inorganic nano-fillers.

The impact of thermal treatment on the mechanical properties and thermal insulation of building materials enhanced with two types of volcanic scoria additives

The need to substitute cement with eco-friendly building materials has increased in recent years, and attempts to enhance the mechanical and thermal insulation properties of these materials are ongoing. Therefore, the present study aims to use two different types of scoria as substitutes for cement in building materials and investigate the impact of thermal treatment on improving mechanical characteristics and thermal insulation. Black and red volcanic scoria, both before and after thermal treatment at different temperatures (600, 700, 800, and 900 °C), were utilized as cement substitutes in concrete specimens. Concrete specimens with different proportions (0-30 % wt.%) of black and red scoria were cured for different durations (14, 21, 28, and 91 days), and then tested for compressive strength. The compressive strength of specimens increased with increasing curing time, but decreased when scoria content exceeded wt.10 %. Furthermore, thermal treatment positively impacted the compressive strength of concrete specimens with red scoria, but negatively affected those with black scoria, owing to the increase in crystalline phases with increasing temperature. The specimen containing 10 % red scoria thermally treated at 900 °C and cured for 91 days yielded the highest compressive strength (60 ± 1.22 MPa). Further, the thermal insulation analysis of the concrete specimens with each type of thermally treated scoria was performed on day 28 of curing. The thermal insulation increased as the proportions of black and red scoria increased, which involved increasing the thermal treatment temperature of both scoria from room temperature to 900 °C on day 28 of curing. Additionally, the thermal insulation of concrete specimens treated with red scoria was more optimized than that of concrete treated with black scoria, particularly at high thermal treatment temperatures, and more than seven times as much as that of ordinary concrete. The lowest thermal conductivity value of the specimen was 0.157 ± 0.01 W m-1 K-1. Based on the findings, concrete with thermally treated red scoria is a suitable eco-friendly building material with high compressive strength and efficient thermal insulation properties.

Improving the comprehensive properties of chitosan-based thermal insulation aerogels by introducing a biobased epoxy thermoset to form an anisotropic honeycomb-layered structure

Naturally-derived aerogels have attracted considerable attention owing to their good biocompatibility, biodegradability and sustainability, but their weak mechanical properties largely limit their applications in various fields. Herein, we proposed the use of a directional freeze-drying method to prepare an anisotropic honeycomb three-dimensional porous aerogel with water-soluble chitosan (CS) as a rigid skeleton and water-soluble biobased epoxy resin as cross-linked hard segments, which had low volume shrinkage and density of 13.9 % and 34.3 mg/cm3, respectively. The resultant aerogel had anisotropic mechanical properties, such as rigidity in the axial direction with a maximum axial modulus of 6.71 MPa, which was 51.6 times larger than that of the pure chitosan aerogel, demonstrating a good compressive elasticity in the radial direction. It also had anisotropic thermal management properties, with a lower thermal conductivity in the radial direction than in the axial direction, down to 0.029 W/mK. The introduction of biobased epoxy resin improved the overall thermal stability, flame retardancy, and increased the biomass content in the aerogel, reducing the carbon footprint of the material. This study paves the way for the construction of a special graded porous, structurally and functionally integrated thermal insulation aerogel, which is of great significance for the development of new thermal insulation materials.

Multifunctional MXene/C Aerogels for Enhanced Microwave Absorption and Thermal Insulation

Two-dimensional transition metal carbides and nitrides (MXene) have emerged as promising candidates for microwave absorption (MA) materials. However, they also have some drawbacks, such as poor impedance matching, high self-stacking tendency, and high density. To tackle these challenges, MXene nanosheets were incorporated into polyacrylonitrile (PAN) nanofibers and subsequently assembled into a three-dimensional (3D) network structure through PAN carbonization, yielding MXene/C aerogels. The 3D network effectively extends the path of microcurrent transmission, leading to enhanced conductive loss of electromagnetic (EM) waves. Moreover, the aerogel's rich pore structure significantly improves the impedance matching while effectively reducing the density of the MXene-based absorbers. EM parameter analysis shows that the MXene/C aerogels exhibit a minimum reflection loss (RLmin) value of - 53.02 dB (f = 4.44 GHz, t = 3.8 mm), and an effective absorption bandwidth (EAB) of 5.3 GHz (t = 2.4 mm, 7.44-12.72 GHz). Radar cross-sectional (RCS) simulations were employed to assess the radar stealth effect of the aerogels, revealing that the maximum RCS reduction value of the perfect electric conductor covered by the MXene/C aerogel reaches 12.02 dB m2. In addition to the MA performance, the MXene/C aerogel also demonstrates good thermal insulation performance, and a 5-mm-thick aerogel can generate a temperature gradient of over 30 °C at 82 °C. This study provides a feasible design approach for creating lightweight, efficient, and multifunctional MXene-based MA materials.

Sensor based dataset to assess the impact of urban heat island effect mitigation and indoor thermal comfort via terrace gardens

This dataset contains temperature variations observed on a building terrace that is partially covered with plantations on one side while the other side remains exposed. The study was conducted at a shelter named "Anbagham" in Tamil Nadu, India. Two sets of temperature and humidity sensors were utilized, with one set placed on the external roofs and the other set placed inside the rooms corresponding to these roofs. The analysis spanned over a period of two months, specifically during the hottest period of the year, totaling 66 days, with measurements taken every hour. The provided dataset can be effectively utilized to examine temperature disparities and patterns in the internal environment attributed to the presence or absence of roof gardens. This research and the accompanying dataset have significant implications for various disciplines. They can aid in the planning and design of energy-efficient buildings, assist green building engineers in estimating internal thermal comfort, enable city/urban planners to estimate land surface temperatures, allow botanists to evaluate the impact of foliage on temperature relief, aid civil engineers in proposing green and insulative roof assemblies, and help mechanical engineers estimate reduced cooling loads and corresponding energy savings.

Foam glasses made from green bottle glass and sugar beet factory lime as a foaming agent

Great waste production alongside limited natural resources represents huge environmental and economic problems worldwide. Sustainable waste management and industrial production can reduce pollution and gain some economic benefits. Eco-friendly thermal insulators such as foam glasses can be produced using secondary raw materials in open-loop recycling. Foam glasses were successfully produced using green bottle glass and sugar beet factory lime (SBFL), CaCO₃-rich waste as a novel foaming agent. Glass powder was mixed with different amounts of SBFL, uniaxially pressed at 20 MPa, and sintered at different temperatures. The influence of sintering temperature and the addition of a foaming agent was examined. Obtained samples were mechanically, thermally, and microstructurally characterized. Results showed that samples sintered at 800 ^°C have the best properties. Obtained foam glasses can be used in a variety of industries where thermal insulation, non-flammability, and non-toxic materials are required.

Multifunctional Hierarchical Metamaterial for Thermal Insulation and Electromagnetic Interference Shielding at Elevated Temperatures

The custom design of lightweight cellular materials is widely concerned due to effectively improved mechanical properties and functional applications. However, the strength attenuation and brittleness behavior hinder honeycomb structure design for the ceramic monolith. Herein, the ceramic matrix composite metamaterial (CCM) with a negative Poisson's ratio and high specific strength, exhibiting superelasticity, stability, and high compressive strength, is customized by combining centripetal freeze-casting and hierarchical structures. CCM maintains a negative Poisson's ratio response under compression with the lowest value reaching -0.16, and the relationship between CCM's specific modulus and density is E ∼ ρ^1.3, which indicates the mechanical metamaterial characteristic of high specific strength. In addition to the extraordinary mechanical performance endowed by hierarchical structures, the CCM exhibits excellent thermal insulation and electromagnetic interference shielding properties, in which the thermal conductivity is 30.62 mW·m^-1·K^-1 and the electromagnetic interference (EMI) shielding efficiency (SE) reaches 40 dB at room temperature. The specific EMI shielding efficiency divided by thickness (SSE/t) of CCM can reach 9416 dB·cm²·g^-1 at 700 °C due to its stability at elevated temperatures, which is 100 times higher than that of traditional ceramic matrix composites. Moreover, the designed hierarchical structure and metamaterial properties provide a potential scheme to implement cellular materials with collaborative optimization in structure and function.

Dual-asymmetrically selective interfaces-enhanced poly(lactic acid)-based nanofabric with sweat management and switchable radiative cooling and thermal insulation

All-weather personal thermal regulation has far been challenged by variable environments especially the regulatory failure caused by highly-dense solar radiation, low environmental radiation and the fluctuated epidermal moisture in different seasons. Herein, from the design of interface selectivity, dual-asymmetrically optical and wetting selective polylactic acid-based (PLA) Janus-type nanofabric is proposed to achieve on-demand radiative cooling and heating as well as sweat transportation. Hollow TiO₂ particles are introduced in PLA nanofabric causing high interface scattering (∼99%) and infrared emission (∼91.2%) as well as surface hydrophobicity (CA > 140°). The strictly optical and wetting selectivity help achieve ∼12.8℃ of net cooling effect under > 1500 W/m² of solar power and ∼5℃ of cooling advantage higher than cotton fabric and sweat resistance simultaneously. Contrarily, the semi-embedded Ag nanowires (AgNWs) with high conductivity (0.245 Ω/sq) endows the nanofabric with visible water permeability and excellent interface reflection for thermal radiation from body (>65%) thus causing ∼7℃ of thermal shielding. Through simple interface flipping, synergistical cooling-sweat reducing and warming-sweat resisting can be achieved to satisfy the thermal regulation in all weather. Compared with conventional fabrics, multi-functional Janus-type passive personal thermal management nanofabrics would be of great significance to achieve the personal health maintenance and energy sustainability.

Multifunctional carbon nanotubes-based hybrid aerogels with high-efficiency electromagnetic wave absorption at elevated temperature

In the complex engineering applications of electromagnetic (EM) wave-absorbing materials, it is insufficient for these materials to exhibit only efficient EM wave attenuation ability. EM wave-absorbing materials featuring numerous multifunctional properties are increasingly attractive for next-generation wireless communication and smart devices. Herein, we constructed a lightweight and robust multifunctional hybrid aerogel consisting of carbon nanotubes/aramid nanofibers/polyimide with low shrinkage and high porosity. The hybrid aerogels exhibit excellent EM wave attenuation, with an effective absorption bandwidth covering the entire X-band from 25 °C to 400 °C. The conductive loss capacity of the hybrid aerogel is enhanced under thermal drive, which results in an enhanced ability to attenuate EM waves, as evidenced by the fact that the best-fit thickness drops from 5.3 to 3.6 mm with increasing temperature. In addition, the hybrid aerogels are capable to efficiently absorb sound waves, with an average absorption coefficient as high as 0.86 at 1-6.3 kHz, and they exhibit superior thermal insulation properties, with a thermal conductivity as low as 41 ± 2 mW/mK. They are thus suitable for applications in the anti-icing and infrared stealth fields. The prepared multifunctional aerogels have considerable potential for EM protection, noise reduction, and thermal insulation in harsh thermal environments.

Thermal insulation impact on overheating vulnerability reduction in Mediterranean dwellings

Heat waves are expected to increase the use of air conditioning (AC), deriving in higher energy consumption. This research aims to determine whether thermal insulation is an effective retrofit strategy for tackling overheating. Four occupied dwellings in southern Spain were monitored: two houses built prior to any thermal criteria and two with current thermal standards. Thermal comfort is assessed considering adaptive models and user patterns for the operation of AC and natural ventilation. Results show that a high level of insulation combined with a proper use of night-time natural ventilation can increase thermal comfort hours under heat waves, lasting 2-5 times longer than in poorly-insulated houses and with up to 2 °C temperature difference at nights. Long-term effectiveness of insulation under extreme heat presents a better thermal performance, especially in intermediate floors. Yet, the activation of AC usually occurs with indoor temperatures of 27-31 °C, regardless of the envelope's solution.

Elastic and compressible Al2O3/ZrO2/La2O3 nanofibrous membranes for firefighting protective clothing

Developing ceramic nanofibrous membranes for the thermal insulation layer of firefighting protective clothing is vital. However, previous ceramic nanofibrous membranes were brittle and easy to break during service in high-temperature environments. The lack of elastic and compressible properties has limited the high-end applications of ceramic nanofibrous membranes. In this work, elastic and compressible Al₂O₃/ZrO₂/La₂O₃ nanofibrous membranes were fabricated via sol-gel electrospinning and calcination in air at different temperatures. The as-fabricated Al₂O₃/ZrO₂/La₂O₃ nanofibrous membranes can maintain excellent elasticity and compressibility in the temperature ranging from -196 to 1400 °C. Moreover, they have low thermal conductivity and high working temperatures. These favorable characteristics make the Al₂O₃/ZrO₂/La₂O₃ nanofibrous membranes a promising candidate for the thermal insulation layer of firefighting protective clothing.

Modification of Hollow Expanded Microspheres with Superior Thermal Insulation Properties and Their Applications

Thermally expandable microspheres (TEMs) are hollow polymeric particles in which a blowing gas has been encapsulated. This property makes them excellent for thermal insulation applications, such as lightweight fillers. This study has developed a viable technology for further improving thermal insulation properties in the field that needs excellent thermal insulation of textile fabrics. The ATO/TEMs composites were designed and prepared to reduce sunlight radiation by the charge gravity method. The test results showed that the ATO-coated TEMs effectively block thermal radiation from sunlight. The temperature difference between ATO/TEMs treated cotton and the uncoated cotton fabric was 9 °C, and the thermal conductivity coatings were 0.0432 W/m⋅K. The UPF value of ATO/TEMs (ILs) coated cotton fabric is 440, significantly higher than pure cotton. This approach can provide insight into the design of high-performance solar insulation composite structures.

Fibrous Aerogels with Tunable Superwettability for High-Performance Solar-Driven Interfacial Evaporation

Solar-driven interfacial evaporation is an emerging technology for water desalination. Generally, double-layered structure with separate surface wettability properties is usually employed for evaporator construction. However, creating materials with tunable properties is a great challenge because the wettability of existing materials is usually monotonous. Herein, we report vinyltrimethoxysilane as a single molecular unit to hybrid with bacterial cellulose (BC) fibrous network, which can be built into robust aerogel with entirely distinct wettability through controlling assembly pathways. Siloxane groups or carbon atoms are exposed on the surface of BC nanofibers, resulting in either superhydrophilic or superhydrophobic aerogels. With this special property, single component-modified aerogels could be integrated into a double-layered evaporator for water desalination. Under 1 sun, our evaporator achieves high water evaporation rates of 1.91 and 4.20 kg m-2 h-1 under laboratory and outdoor solar conditions, respectively. Moreover, this aerogel evaporator shows unprecedented lightweight, structural robustness, long-term stability under extreme conditions, and excellent salt-resistance, highlighting the advantages in synthesis of aerogel materials from the single molecular unit.

Thermal Insulation of Protective Clothing Materials in Extreme Cold Conditions

Background

Thermophysiological comfort in a cold environment is mainly ensured by clothing. However, the thermal performance and protective abilities of textile fabrics may be sensitive to extreme environmental conditions. This article evaluated the thermal insulation properties of three technical textile assemblies and determined the influence of environmental parameters (temperature, humidity, and wind speed) on their insulation capacity.

Methods

Thermal insulation capacity and air permeability of the assemblies were determined experimentally. A sweating-guarded hotplate apparatus, commonly called the "skin model," based on International Organization for Standardization (ISO) 11092 standard and simulating the heat transfer from the body surface to the environment through clothing material, was adopted for the thermal resistance measurements.

Results

It was found that the assemblies lost about 85% of their thermal insulation with increasing wind speed from 0 to 16 km/h. Under certain conditions, values approaching 1 clo have been measured. On the other hand, the results showed that temperature variation in the range (-40°C, 30°C), as well as humidity ratio changes (5 g/kg, 20 g/kg), had a limited influence on the thermal insulation of the studied assemblies.

Conclusion

The present study showed that the most important variable impacting the thermal performance and protective abilities of textile fabrics is the wind speed, a parameter not taken into account by ISO 11092.

Aramid nanofibers supported metal-organic framework aerogel for protection of chemical warfare agent

Protective fabrics containing Zr-Based Metal-Organic Frameworks (Zr-MOFs) show great potential in the detoxification of chemical warfare agents (CWAs). However, the current studies still face the challenges of complicated fabrication processes, limited MOF loading mass, and insufficient protection. Herein, we developed a lightweight, flexible and mechanical robust aerogel by in situ growth of UiO-66-NH₂ onto aramid nanofibers (ANFs) and assembly of UiO-66-NH₂ loaded ANFs (UiO-66-NH₂@ANFs) into 3D hierarchically porous architecture. The UiO-66-NH₂@ANF aerogels feature high MOF loading of 261 %, high surface area of 589.349 m² g^-1, open and interconnected cellular structure, which provide efficient transfer channels and promote catalytic degradation of CWAs. As a result, the UiO-66-NH₂@ANF aerogels demonstrate high 2-chloroethyl ethyl thioether (CEES) removal rate at 98.9 % and a short half-life of 8.15 min. Moreover, the aerogels present good mechanical stability (recovery rate of 93.3 % after 100 cycles under 30 % strain), low thermal conductivity (λ of 25.66 mW m^-1 K^-1), high flame resistance (LOI of 32 %) and good wearing comfortableness, indicating promising potential in multifunctional protection against CWAs.

Cellulose-based, flexible polyurethane polyHIPEs with quasi-closed-cell structures and high stability for thermal insulation

Cellulose-based, closed-cell porous materials templated from emulsions are promising for thermal insulation, but their low stability imposed by physical interaction hinders the materials from real applications. Herein, we report the fabrication of cellulose-based, flexible polyurethane polyHIPEs with quasi-closed-cell structures, high stability and flexibility for thermal insulation. The polyHIPEs were prepared from cellulose-stabilized Pickering high internal phase emulsions through interfacial crosslinking using isocyanate. The resulting polyurethane polyHIPEs showed controllable external shapes, quasi-closed-cell structures, high flexibility, low density, and robust compression (without fracture even after compression to 30 % original height). The crosslinking enabled the polyHIPEs to show hydrophobicity, good stability (without breakage and dissolution observed after immersing in NaOH solution at pH 12, HCl solution at pH 1 and hot water at 100 °C, for 24 h) and decreased moisture uptake (below 1 %). The low density and quasi-closed-cell structures endowed the polyHIPEs with high thermal insulation, with thermal conductivity as low as 33.1 mW/(m K). These features make the cellulose-based, closed-cell polyHIPEs as an excellent candidate for thermal insulting.

Improved thermal insulation and compressive property of bimodal poly (lactic acid)/cellulose nanocomposite foams

In this work, an innovative PLA/CNF nanocomposite foam with a bimodal cell structure is prepared by a simple one-step depressurization foaming process using only supercritical carbon dioxide (ScCO₂) as the foaming agent. Only at a specific foaming temperature, PLA/CNF nanocomposites foam with a bimodal cell structure could be obtained. According to the different crystallization kinetics and nucleation efficiency of samples, it was inferred that the crystallization rate and phase interface would affect the cell structure. The prepared PLA/CNF nanocomposite foam with a bimodal cell structure had an expansion ratio as high as 20 times and thermal conductivity of 0.041 w m^-1 k^-1, which exhibited low density and excellent thermal-insulation property. Meanwhile, the PLA/CNF nanocomposite foam exhibited excellent compression performance due to the presence of CNFs, which showed promising application in packaging and construction materials.

Thermal and mechanical properties of coal gasification slag based foam concrete

Foam concrete possesses low density and excellent thermal insulation properties and has been widely used in construction industry. Considering the recycling and reusing of coal gasification slag (CGS), a solid waste product in the coal chemical industry, CGS was used as the supplementary cementations material to prepare foam concrete (CGS-FC) in this work. The influence of the CGS content and water-binder ratio on the pore structure, mechanical and thermal properties was investigated. The results show that the CGS content and water-binder ratio directly impact the fluidity of the slurry, which affects the internal pore structure of the specimens after molding. And a CGS-FC with a compressive strength of 6.89 MPa, thermal conductivity of 0.24 W/m K, and a bulk density of 867 kg/m³ was successfully produced when the CGS content was 30% and water-binder ratio was 0.5. In particular, the utilization of CGS to prepare foam concrete product has recycling efficiency and environmental benefit.

Morphology of coat and skin of small ruminants reared in the Brazilian semi-arid region

The structure of the coat and integument of small ruminants reared in semi-arid regions have valuable characteristics that favor their adaptation to the region. The objective of this study was to evaluate the structural characteristics of the coat and integument and sweating capacity of goats and sheep in the Brazilian semi-arid region, using 20 animals, 10 of each breed, 5 males and 5 females of each species, grouped in a completely randomized design in a 2 x 2 factorial scheme (2 species and 2 genders) with 5 replicates. The animals were already being kept under the influence of high temperatures and levels of direct solar radiation before the day of the collections. At the time of the evaluations, ambient temperature was high, with low relative humidity. The pattern of epidermal thickness and sweat glands per body region was superior in sheep (P < 0.05), and the number of hair follicles and sweat rate were similar (P > 0.05) between the species. There was no difference (P > 0.05) in the evaluated characteristics between the genders, showing that they are not influenced by hormones. The morphology of the coat and skin of these animals showed a superiority of goats compared to sheep.

Clothing air gaps in various postures in firefighters' work

Both the physical properties of the fabric materials used in clothing and the effective design of the clothing, primarily in terms of the air gap thickness, restrict the transmission of the thermal energy from the heat source to the firefighter's body. The air gap distribution over the body in real deployment conditions of firefighters will vary, and is likely to be different from the air gap distribution in standardised manikin tests in standing upright posture. In this study, we investigated differences in the distribution of air layers in firefighters' clothing in three postures reflecting realistic on-duty exposure conditions (crawling, hose-holding, and standing upright used in laboratory tests) using 3D body scanning technology. The body posture induced substantial changes in the air gap thickness on the upper body (chest and back) and lower body. These changes were reflected in both the thermal and evaporative resistance of the ensemble, and consequently, in their potential thermal performance in the field. Therefore, it is recommended to consider body postures during the evaluation of clothing protective performance. Secondly, the knowledge of local clothing properties in real-life exposure provides a true protection mapping and gives design inputs to improve the local protective properties of firefighters' clothing.

Superelastic and multifunctional fibroin aerogels from multiscale silk micro-nanofibrils exfoliated via deep eutectic solvent

Superelastic silk fibroin (SF)-based aerogels can be used as multifunctional substrates, exhibiting a promising prospect in air filtration, thermal insulation, and biomedical materials. However, fabrication of the superelastic pure SF aerogels without adding synthetic polymers remains challenging. Here, the SF micro-nano fibrils (SMNFs) that preserved mesostructures are extracted from SF fibers as building blocks of aerogels by a controllable deep eutectic solvent liquid exfoliation technique. SMNFs can assemble into multiscale fibril networks during the freeze-inducing process, resulting in all-natural SMNF aerogels (SMNFAs) with hierarchical cellular architectures after lyophilization. Benefiting from these structural features, the SMNFAs demonstrate desirable properties including ultra-low density (as low as 4.71 mg/cm³) and superelasticity (over 85 % stress retention after 100 compression cycles at 60 % strain). Furthermore, the potential applications of superelastic SMNFAs in air purification and thermal insulation are investigated to exhibit their functionality, mechanical elasticity, and structural stability. This work provides a reliable approach for the fabrication of highly elastic SF aerogels and endows application prospects in air purification and thermal insulation opportunities.

Recycling of marble cutting waste additives in fired clay brick structure: a statistical approach to process parameters

Within the scope of the present study, the marble cutting waste, which is an industrial waste of different sizes (< 75 µm and < 150 µm), was incorporated into the clay structure at various rates and a total of 36 series bricks were produced. The brick mixtures were prepared by the semi-dry molding method and the brick specimens were sintered for three temperatures (850 °C, 950 °C, and 1050 °C). The fired bricks containing marble cutting waste with a lower particle size (75 µm) have higher compressive strength. However, all samples produced can meet the relevant standard requirements in terms of compressive strength. Thermal conductivity decreased from 1.008 to 0.775 W/mK with the incorporation of marble cutting waste, a decrease of approximately 23.11%. The effects of grain size, firing temperature, and marble cutting waste concentration on the quadratic model were statistically determined by variance analysis (ANOVA). According to statistical findings, the order of importance of design factors for brick properties (except for compressive strength) is marble cutting waste > firing temperature > particle size. For compressive strength, the most dominant factor is amount of marble cutting waste, followed by particle size and firing temperature, respectively. Consequently, the results suggest that marble cutting waste does not need to be reduced to smaller particle sizes to improve the fired clay brick properties.

Effect of a low content of waste rubber inclusion on pore structure and thermal insulation properties of hybrid slag mortars

The reuse of sustainable waste materials in cement-based mixtures is a key solution for the production of environmentally friendly construction materials. Among the various types of industrial wastes, the utilization of waste rubber (WR) has become a vital topic in the sustainable material design. This study aimed at developing an eco-friendly mortar by enhancing the use of WR as a cement additive in hybrid slag mortar mixtures. For this purpose, five different hybrid slag mixtures were prepared, with three contents (0%, 1.0%, and 2.0%) and two different particle size ranges (0-0.6 mm and 0-1.0 mm) of WR. The experimental results demonstrate that the incorporation of a low content of WR into the mixtures leads to a major pore modification effect, resulting in an increase in the number of pores with lower pore sizes. Based on the pore modification effect, a thermal insulation enhancement of ≈17% was measured with limited strength reductions. Besides, strong linear relationships between the strengths and the effective pore contents with R² of > 0.80 were detected. With the aim of promoting the sustainable design, the integration of a low content of rubber and slag seems as a good option.

Thermal insulation and antibacterial foam templated from bagasse nanocellulose /nisin complex stabilized Pickering emulsion

Foam packaging with good thermal insulation and antibacterial properties is promising for cold chain delivery to strengthen food safety. This study reports a novel antibacterial foam with thermal insulation templated from bagasse nanocellulose complex particle-stabilised acrylate epoxy soybean oil (AESO) Pickering emulsions. Nanocellulose/nisin complex particles (N-CNFs) were prepared by loading positively charged nisin onto negatively charged cellulose nanofibrils via electrostatic interactions, that highly enhanced the stability of nanocellulose at the AESO/water interface and imparted the corresponding foam with good antibacterial properties. The results show that the porosity of the foam prepared with N-CNFs increased from 10.9% to 29.9% compared with that of the foam corresponding with bare nanocellulose; the thermal conductivity of the N-CNF foam decreased substantially from 0.431 W/m·K to 0.197 W/m·K. Moreover, the prepared foam exhibited good antibacterial activity, and its bacteriostatic rate against Listeria monocytogenes was 91.33%. The incorporation of antibacterial peptides into nanocellulose has enriched the study of the Pickering emulsion templating method for preparing multifunctional foam materials and is expected to broaden the application of nanocellulose in the field of food packaging.

Physical, mechanical, and thermal properties of concrete roof tiles produced with vermiculite

This study aimed to evaluate the effect of using expanded vermiculite and its impact on the production of concrete roof tiles. The control treatment and replacement of 12.5, 25, 37.5, and 50% sand by vermiculite were evaluated. The concrete roof tiles were moulded by the simultaneous pressing and extrusion mechanical process. The control trace was comprised by 21.95% CPV-ARI cement, 65.85% sand, and 12.20% limestone. After production, the concrete roof tiles were cured for 28 days. The physical (roof tiles classification, samples dry weight, water absorption, and porosity), mechanical (splitting tensile strength), and microstructural properties were evaluated. All treatments were assessed before and after accelerated ageing. The thermal properties of the modification in the concrete roof tiles' composition were also analysed. The evaluated amounts of vermiculite significantly affected the physical, mechanical, and thermal properties of concrete roof tiles. The use of vermiculite in concrete roof tiles reduced their dry weight and thermal conductivity, not impairing their durability. The use of 31.0% vermiculite in concrete roof tiles was suggested for better thermal insulation optimization (20.29% reduction) and weight reduction (7.92% and 7.94% at 28 days of curing and after accelerated ageing, respectively), along with adequate physical, mechanical, and durability properties.

Microcellular injection molded lightweight and tough poly (L-lactic acid)/in-situ polytetrafluoroethylene nanocomposite foams with enhanced surface quality and thermally-insulating performance

High-performance microcellular polymer foams have been widely used all over the world, while the excessive usage of petroleum-based polymers caused serious environmental problems. As the eco-friendly awareness is increasing significantly, poly (L-lactic acid) (PLLA), as a typical biomass polymer, has gradually attracted widespread attention. However, the slow crystallization and poor melt strength of PLLA lead to low foaming ability and thus limiting its industrial applications. Herein, a novel and scalable strategy by coupling in-situ fibrillation and mold-opening microcellular injection molding (MOMIM) was developed to fabricate lightweight and tough PLLA/polytetrafluoroethylene (PTFE) foams. Thanks to the reticulated in-situ PTFE nanofibrils with a diameter of 100-200 nm, the crystallization and viscoelasticity of PLLA were dramatically promoted, and further contributing to its foaming ability. The expansion ratio of the MOMIM PLLA/PTFE foam was increased by 86 % compared with the regular microcellular injection molded (RMIM) PLLA foam. Moreover, the lower foam density and the toughening effect of PTFE nanofibrils resulted in the outstanding ductility of the PLLA/PTFE foams, whose tensile elongation, flexural strength, and impact strength were maximally increased by 52 %, 28 %, and 48 %, compared with PLLA foams. More importantly, the thermally-insulating performance and surface quality of PLLA/PTFE foams were also greatly improved.

High-performance multifunctional polyvinyl alcohol/starch based active packaging films compatibilized with bioinspired polydopamine nanoparticles

Bioinspired polydopamine (PDA) nanoparticles were synthesized and explored as functional compatibilizers in polyvinyl alcohol/starch (PVA/ST) matrix to develop high-performance multifunctional packaging film. The effect of the addition of PDA on the microstructural, mechanical, thermal, water vapor barrier, ultraviolet (UV)/high-energy blue light (HEBL) blocking, thermal insulating and antioxidant properties of PVA/ST composite films was fully investigated. Results demonstrated that the added PDA nanoparticles were evenly dispersed in the PVA/ST matrix, providing compact and dense nanocomposite films due to their compatibilization effect. Compared with virgin PVA/ST film, the resulting PVA/ST/PDA nanocomposite films exhibited greatly improved tensile strength, toughness, thermal stability, and water vapor barrier ability. Furthermore, the presence of PDA endowed PVA/ST composite film with excellent UV/HEBL blocking, thermal insulating as well as antioxidant functions. Thus, such high-performance multifunctional nanocomposite films hold the potential of protecting food quality against photothermal oxidative deterioration and extend food shelf life.

Recent advances in tailoring and improving the properties of polyimide aerogels and their application

With the rapid advancements in technology and growing aerospace applications, there is a need for effective low-weight and thermally insulating materials. Aerogels are known for their ultra-lightweight and they are highly porous materials with nanopores in a range of 2 to 50 nm with very low thermal conductivity values. However, due to hygroscopic nature and brittleness, aerogels are not used commercially and in daily life. To enhance the mechanical and hydrophobic properties, reinforcement materials such as styrene, cyanoacrylates, epoxy along with hydroxyl, amines, vinyl groups are added to the surface. The addition of organic materials resulted in lower service temperatures which reduce its potential applications. Polyimides (PI) are commonly used in engine applications due to their suitable stability at high temperatures along with excellent mechanical properties. Previous research on polyimide aerogels reported high flexibility or even foldability. However, those works' strategy was mainly limited to altering the backbone chemistry of polyimide aerogels by changing either the monomer's compositions or the chemical crosslinker. This work aims to summarize, categorize, and highlight the recent techniques for improving and tailoring properties of polyimide aerogels followed by the recent advancements in their applications.

Magnesium hydroxide coated hollow glass microspheres/chitosan composite aerogels with excellent thermal insulation and flame retardancy

The development of an environmental-friendly thermal insulation and flame retardant material has attracted widespread attention in modern architecture. In this work, a kind of novel aerogel composites were prepared by incorporation of Mg(OH)₂ coated hollow glass microspheres (HGM) into chitosan (CSA) matrix and then cross-linking by glutaraldehyde (abbreviated as CSA-HGM-Mg(OH)₂). The as-prepared composite aerogel exhibits vertical directional channel with high porosity and excellent thermal insulation with a low thermal conductivity of 0.035 W m^-1 k^-1. Besides, it shows excellent flame retardancy with a high limit oxygen index (LOI) value up to 50.8, which is one of the highest values among the most of flame retardants reported previously. Also, a very low peak heat release rate (pHRR) of 24.12 kW m^-2 was obtained which makes the aerogel composite reaching UL-94 V-0 rating. Such results may be attributed to a synergy effect by combination of its abundantly porous structure derived from HGM to give a better thermal insulation and excellent nonflammability of CSA and Mg(OH)₂ to offer a superior flame retardancy. Taking advantages of its high mechanical strength, low cost materials, simple and scalable preparation method, CSA-HGM-Mg(OH)₂ aerogel composites may hold great potential for future thermal insulation and flame retardant applications.

Monolithic carbon aerogels within foam framework for high-temperature thermal insulation and organics absorption

Carbon aerogels exhibit high porosity, good electrical conductivity, and low thermal conductivity, but their practical applications are greatly hindered by their tedious preparation and inherent structure brittleness. Herein, monolithic carbon aerogels (MCAs) with low density and large size are prepared via a facile sol-gel polymerization of phenolic resin within melamine foam (MF), followed by ambient pressure drying and co-carbonization. During ambient pressure drying process, the MF matrix can deliver supporting force to counteract against the solvent evaporation surface tension, thus inhibiting volume shrinkage and shape deformation. Upon co-carbonization process, the MF matrix and organic aerogel could pyrolyze and shrink cooperatively, which could effectively prevent the brittle fracture of monolith. Therefore, large-sized MCAs (up to 250 × 250 × 20 mm) with low densities of 0.12-0.22 g·cm^-3 are obtained. The as-obtained MCAs possess high compressive strength (2.50 MPa), ultra-low thermal conductivity (0.051 W·m^-1·K^-1 at 25 °C and 0.111 W·m^-1·K^-1 at 800 °C), and high-volume organic absorption capability (77.3-88.0%, V/V). This facile and low-cost method for the fabrication of large-sized monolithic carbon aerogels with excellent properties could envision enormous potential for high-temperature thermal insulation and organics absorption.

Soil-Cement Bricks Development Using Polymeric Waste

This research aimed to evaluate the effect of adding different polymeric waste percentages and types on the physical, mechanical, thermal, and durability properties of soil-cement bricks. Tire and polyethylene terephthalate (PET) waste were evaluated at 1.5 and 3.0% (mass/mass). The soil was characterized in terms of shrinkage, compaction, consistency limits, particle size, and chemical analyses, whereas the waste particles were submitted to morphological characterization. The bricks were produced in an automatic press with a 90:10 (mass/mass) soil:cement ratio. The soil-cement bricks were characterized by density, moisture, water absorption, loss of mass by immersion, compressive strength, thermal conductivity, and microstructural analysis. PET waste stood out for its use as reinforcement in soil-cement bricks. The best performance was obtained for bricks reinforced with 1.5% PET, which showed a significant compressive strength improvement, meeting the marketing standards criteria, even after the durability test, as well as obtaining the lowest thermal conductivity values. The percentage increase from 1.5 to 3.0% fostered a significant water absorption and loss of mass increase, as well as a significant compressive strength reduction of the bricks.

Shape-recoverable, piezoresistive, and thermally insulated xerogels based on nanochitin-stabilized Pickering foams

Biomass-derived porous materials are promising for various fields and preferred for sustainable development. In this work, shape-recoverable nanochitin-based xerogels with porous structure and excellent mechanical strength, thermal insulation (43.23 ± 0.17 mW/m·k) and piezoresistive properties were prepared by nanochitin-stabilized Pickering foams with chemical crosslinking for the first time through simple air-drying. At the optimized ingredients of nanochitin, surfactant (T80) and crosslinker (glutaraldehyde), the Pickering foams exhibited no significant collapse after one week, and the xerogels prepared thereof achieved a mechanical strength of 0.5-2.7 MPa at 80% strain and considerable structural stability after 100 cycles at 60% strain. Moreover, the resistance of the xerogel had a high linearity in the strain range (0-10%) and could recover to the initial value after 20 cycles. Notably, this is the first time that pure bio-based conductive xerogel has been obtained. These features make nanochitin a promising candidate for biodegradable and sustainable 3D porous materials.