Excellent Thermal Insulation Properties Research Articles

Ultra-elastic and super-insulating biomass PEBA nanoporous foams achieved by combining in-situ fibrillation with microcellular foaming

High-performance thermal insulation materials play a critical role in thermal management and saving energy. The current conventional thermal insulation materials cannot meet the increasing requirements of thermal management for thermal insulation performance. The advanced insulating materials represented by silica aerogels have excellent thermal insulation properties, but the brittleness limits their applications. Herein, we reported a flexible and environmentally friendly method to prepare ultra-elastic and super-insulating bio-based nanocellular material by means of microcellular foaming of in-situ fibrillated PA reinforced PEBA nanocomposites with the mixture of CO2 and N2 as blowing agents. Thanks to the significantly reduced air thermal conductivity within nanoscale cells, the nanoporous foam exhibits outstanding thermally insulating properties with a thermal conductivity of as low as 25.6 mW/m K. More importantly, the nanoporous foam also shows excellent compression and stretch resilience and outstanding flexibility. The excellent thermal insulation, ultra-elasticity, biomass and biodegradability, environmental friendliness, and manufacturing scalability make the material attractive for high-performance thermal management applications.

Wood‐Based, Bifunctional, Mulberry‐Like Nanostructured Black Titania Evaporator for Solar‐Driven Clean Water Generation

Developing an integrative and highly performant solar evaporator is essential for a solar steam generation technology to alleviate clean water scarcity. Herein, a bioinspired mulberry‐like black titanium dioxide loading on the surface of wood (BTW) as a solar absorber is constructed. Mulberry‐shaped black titanium dioxide nanoparticles not only possess outstanding full‐spectrum light absorption, but also multiple refractions and scattering of light are obtained by the special groove structure. The wood substrate provides natural and vertical water channels, resulting in excellent water transport and thermal insulation properties. Under a simulated light of 1 kW m−2, the BTW achieves an evaporation rate of 2.04 kg m−2 h−1 and has a high solar steam efficiency of 90.06%. In addition, the black titanium dioxide exhibits an excellent photocatalysis degradation ability, which is able to achieve 90% degradation of the methyl orange and 50% degradation of the tetracycline solution. The bifunctional solar evaporator is capable of simultaneous desalination and degradation of organic pollutants, while opening up a new approach in the field of clean water generation.

Research on Acoustic Absorption Properties of Aramid Honeycomb Composite Material Reinforced by Polyimide Foam

To endue sound absorption behavior for aramid honeycomb core (ARHC), isocyanate‐based polyimide foam (IBPIF) with excellent thermal insulation and acoustic properties produced by a new formulation of foaming slurry is filled into ARHC by the free foaming route. As a core factor to adjust the cellular structure of IBPIF, the effect of water dosage on the acoustic behavior of IBPIF and IBPIF filled ARHC (IBPIF/ARHC) is studied, and the optimal formula to produce IBPIF/ARHC is filtered out. Results suggest that water dosage effectively regulates the cellular structure of IBPIF. When water dosage is 7.2 g, IBPIF has a large windows opening rate, which plays a positive role in sound absorption performance. IBPIF/ARHC‐3 has the best sound absorption property, which possesses a maximum sound absorption coefficient (α) of 0.9 at 1500 Hz. Its average α increases to 0.78 and shows an increase of 680% compared to ARHC. Meanwhile, the density of IBPIF/ARHC is only about 59 kg m−3. In 300–600 Hz range, IBPIF‐3 and ARHC show obvious synergy effects in sound absorption behavior. The average α of IBPIF‐3 and ARHC is only 0.3 and 0.06, respectively, and that of IBPIF/ARHC‐3 reaches up to 0.42. The thermal insulation performance of ARHC is also improved, and thermal conductivity decreases from 0.067 to 0.047–0.049 W (m K)−1.

Thermal insulation and anti-vibration properties of MoSi2-based coating on mullite fiber insulation tiles

Thermal protection materials with excellent thermal insulation properties and high reliability are crucial for aerospace vehicle. Mullite fiber insulation tiles coated with MoSi2-borosilicate glass ([email protected]2) were prepared by a simple slurry method. Results shown that the surface temperature rapidly reached 1043.1 °C under the heat flux of 450 kW/m2, while the cold-surface remained at room temperature. The adjusting effects of MoSi2-based coating on the thermal response and transfer properties of MFIT were investigated systematically. Compared with MFIT, the surface and internal temperatures of [email protected]2 were obviously suppressed, due to the existence of MoSi2-based coating with high emissivity, which effectively enhanced the thermal radiation of the surfaces. Finally, the structural reliability under coupled environment of heating (q0 = 450 kW/m2) and random vibration with high magnitude (20–2000 Hz, Grms = 20 g) was also investigated. Destructive cracking and peeling of the coating were not observed, due to the excellent bonding strength between the coating and the substrate. The results provided an important basis for the potential application of insulation tiles with mullite fibers in aerospace vehicles and the design of lightweight thermal protection systems.

Investigation of foamed glass using natural waste materials as foaming agent

The use of high-quality thermal insulation materials to improve the energy efficiency of buildings is strongly increasing. Foam glass, a durable and porous material that is resistant to almost all substance effects, is one of the best thermal insulation materials. Glass foaming is a complicated process that is affected by the types of foaming agents used in the initial composition of the mixture and the mode of foaming. The influence of all components of the mixture - glass matrix and foaming agent - is discussed in this paper. Three types of glass powder (alkali frit, soda-lime silicate and borosilicate) were determined to be the matrix material. The foaming agents generate a gas phase via thermal decomposition of eggshell or a chemical reaction with the oxygen in the molten glass via SiC and coffee ground waste. The powder compacts fired at 900 °C for 10 minutes with a foaming agent content of 2 wt % presented excellent thermal insulation properties by using soda-lime silicate glass with SiC and eggshell foaming agents mixtures. The coffee ground waste-glass mixtures show inferior thermal insulation properties with each different glass powder.

Silica-Bacterial Cellulose Composite Aerogel Fibers with Excellent Mechanical Properties from Sodium Silicate Precursor.

Forming fibers for fabric insulation is difficult using aerogels, which have excellent thermal insulation performance but poor mechanical properties. A previous study proposed a novel method that could effectively improve the mechanical properties of aerogels and make them into fibers for use in fabric insulation. In this study, composite aerogel fibers (CAFs) with excellent mechanical properties and thermal insulation performance were prepared using a streamlined method. The wet bacterial cellulose (BC) matrix without freeze-drying directly was immersed in an inorganic precursor (silicate) solution, followed by initiating in situ sol-gel reaction under the action of acidic catalyst after secondary shaping. Finally, after surface modification and ambient drying of the wet composite gel, CAFs were obtained. The CAFs prepared by the simplified method still had favorable mechanical properties (tensile strength of 4.5 MPa) and excellent thermal insulation properties under extreme conditions (220 °C and −60 °C). In particular, compared with previous work, the presented CAFs preparation process is simpler and more environmentally friendly. In addition, the experimental costs were reduced. Furthermore, the obtained CAFs had high specific surface area (671.3 m²/g), excellent hydrophobicity, and low density (≤0.154 g/cm3). This streamlined method was proposed to prepare aerogel fibers with excellent performance to meet the requirements of wearable applications.

Time-dependent high-temperature compressive failure behavior of high-silica/boron-phenolic composites modified with boron carbide and talc

Polymer-based composites with high strength-to-weight ratio and excellent thermal insulation properties are widely used in aerospace thermal structures as thermal protection materials. In this work, high-silica/boron-phenolic composites modified with boron carbide (B4C) and talc are shown to exhibit improved thermal stability due to oxidation that occurs between 600 °C and 1000 °C. The oxidation reaction was verified and explained by the results of thermogravimetric analysis coupled with Fourier transform infrared spectroscopy. Temperature-dependent compression experiments were conducted for B4C-talc modified high-silica/boron-phenolic composites held for different holding times (ranging from 0.5 to 2 h) and loaded in two different directions (along the warp and along the weft). Digital microscopy and scanning electron microscopy were used to analyze the failure morphology of the tested specimens at different scales. It was found that the compressive strength of the composite specimen shows sensitivity against the fiber undulation, test temperature and the holding time in the high-temperature environment. Different trends were observed when varying the holding time at different temperatures: compressive strength increased at temperatures up to 130 °C, decreased between 340 and 560 °C, and slightly increased between 780 and 1000 °C. Three failure modes were observed with increasing temperature: shear failure of the fiber bundles at 25–340 °C, delamination at 560 °C, and fiber buckling at 780–1000 °C. These findings provide basic thermal and mechanical data for B4C-talc modified high-silica/boron-phenolic composites that can contribute to the design of thermal protection structures with greater integrity and higher reliability.

Microextrusion Foaming of Polyetheretherketone Fiber: Mechanical and Thermal Insulation Properties

Porous polyetheretherketone (PEEK) materials, especially those with controllability and excellent mechanical properties, have always been the development hotspots in the fields of thermal insulation and medical bone implants. However, the traditional sulfonation process of porous PEEK materials has the problems of applying abundant high‐concentration solvents, high production costs, low resource utilization, and environmental pollution. Herein, a microextrusion foaming process with using CO2as a blowing agent is proposed for creating porous PEEK fibers under different parameters. The as‐prepared porous PEEK fiber possesses well‐defined cell morphology, high toughness (136.2%), and excellent thermal insulation properties (13.4 ± 1.50 °C), resulting from the high cell nucleation rate and limited‐time cell growth (<0.85 s). All in all, the microextrusion foaming process provides unprecedented opportunities for continuous manufacturing and functional development of porous PEEK fibers.

A facile method to prepare high-performance thermal insulation and flame retardant materials from amine-linked porous organic polymers

Developing porous functional materials with good thermal insulation and flame retardant properties is of great importance in modern eco-friendly buildings. Herein, we report the one-step synthesis of imine chain monolithic porous phosphorus-containing organic porous polymers (PPOPs) using Schiff base polycondensation reaction and as an example of efficient thermal insulation and flame retardant. Experimental results show that the PPOPs have low thermal conductivity (0.055 W·m−1·K−1) and excellent flame retardant properties. Measurements by microcalorimetry (MCC) showed a peak heat release rate (pHRR) value was 23.9 W·g−1, which is nearly an order of magnitude lower than that of most currently reported flame retardant materials. Using PPOPs in the epoxy resin (EP) matrix, the prepared EP composites exhibited excellent flame retardant properties. Cone calorimeter (CC) tests showed that the peak heat release rate (pHRR) and peak smoke release rate (pSPR) during combustion of PPOPs/EP composites were reduced by 42.0% and 36.4%, respectively, compared with pure EP. Tensile tests showed that the addition of PPOPs improved the mechanical properties of the composites to some extent. In addition, PPOPs can be designed into different shapes for practical applications compared with those fragile inorganic insulation materials and powders that were usually non-processable. Taking these advantages into account, PPOPs have great potential for modern building applications as monolithic foams or coatings with both excellent flame retardancy and thermal insulation properties.

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.

Origin of Carpathian ozokerite deposits: determined from biomarkers and aromatic hydrocarbons distributions

Ozokerite deposits are rare, but their occurrences and origins can significantly contribute to studies of petroleum systems. Due to the excellent thermal and electrical insulation properties, ozokerite could be used in the energy sector, e.g., in the construction of heat storage tanks or in medicine to treat various ailments. In this study, the origin and process of ozokerite deposits formation are explained based on gas chromatography coupled with mass spectrometry (GC–MS) of oils, rock extracts, and ozokerite samples. The analyzed samples represent the most famous European ozokerite deposits, which are located in the Ukrainian Outer Carpathians, at Starunia and Boryslav. The results indicate that these ozokerites were generated from the source rocks that hosted mainly type II or II/III kerogen. These types of kerogen occur in the Oligocene-age Menilite Beds in Boryslav-Pokuttya and Skyba tectonic units of the Outer Carpathians. Our study demonstrates that, the ozokerite deposits are a product of geochromatographic effect - chromatography-like interaction between hot carrier gas (e.g., CO2), migrating oil and siliciclastic host rocks, which partially influence n-alkanes and linear-isoprenoid distribution but leave steranes and terpanes changed the least or unchanged.

Asbestos Removal Acceleration for New Jobs and Fossil Fuel Use Reduction for Public Health and Climate Readiness: A Contribution to the Revival of the Italian Economy Post-COVID-19.

The Italian economy has been battered by the SARS-CoV-2/COVID-19 pandemic. European Union and Italian government economic recovery funds will provide special economic recovery loans aimed toward energy saving and the consequent reduction of greenhouse gas emissions (GHG) to meet the Paris Agreement climate goals. In, Italy, millions of square meters of asbestos cement (AC) roofing cover industrial and civic buildings. Removal of this asbestos containing material (ACM) would contribute to three pandemic and economic recovery objectives: job creation, reduction of greenhouse gasses (thru energy savings), and public health improvements. Though asbestos was used for its excellent thermal insulation properties, we provide calculations that demonstrate that the cement binding in AC roofing negates the asbestos insulation function. Therefore, replacing AC roofing with roofs made with alternative materials with better thermal transmission coefficients can contribute significantly to energy savings, reduce the risk of asbestos-related morbidity and mortality, and establish substantial economic activity.

Thermal properties of carbon nanofibers enhanced lightweight cementitious composite under high temperature

Foam concrete is conventionally used in non-structural applications (e.g. thermal and acoustic insulation) due to its lightweight nature and poor mechanical properties. However, interest in adopting foam concrete as structural components has increased phenomenally in recent years due to its lightweight and sustainable feature. A new type of foam concrete termed as carbon nanofibers enhanced lightweight cementitious composite (CNF-LCC) was developed by blending micro-foam bubbles with carbon nanofibers enhanced ultra-high performance concrete; it has superior mechanical properties, long-term properties and bond performance with steel bar compared with conventional foam concrete. In this paper, thermal properties of CNF-LCC during heating were investigated and compared with normal weight concrete (NWC) and lightweight aggregate concrete (LWAC). From room temperature to 800 ℃, the thermal diffusivity of CNF-LCC was lower than NWC and similar to LWAC while the specific heat and thermal conductivity of CNF-LCC was lower than both NWC and LWAC. CNF-LCC showed better structural efficiency than NWC and LWAC in combination of mechanical and thermal insulation properties. The measured thermal insulation properties under high temperature were verified by conducting one-dimensional heat transfer tests and numerical analysis on CNF-LCC blocks. Furthermore, the thermal strain of CNF-LCC during heating is lower and more stable than NWC and LWAC. Dehydration reaction at isothermal elevated temperature was characterised for the analysis of experimental results. Foam bubbles could reduce both thermal insulation and strain properties while a low dosage of CNFs had minimum effect on the thermal insulation properties but could improve the mechanical properties and decrease the thermal shrinkage. CNF-LCC showed potential for fire resistant as a structural lightweight concrete due to the excellent thermal insulation and lower thermal strain properties.

Influence of foam density on burning behavior of polymer bead foams

AbstractFoamed plastics are increasingly employed due to the high demand in functional materials with reduced weight. Bead foams in general offer low weight and excellent thermal insulation properties combined with extremely high freedom in design. Though foams show increased risk of ignition and heightened heat release, literature on burning behavior is rather limited. Therefore, this study investigates density‐dependent burning behavior of commercial bead foams like expanded polypropylene (EPP) and expanded modified polyphenyleneether (E‐mPPE) by cone calorimetry. The results are compared to existing studies on the density‐dependent burning behavior of different foams, mainly expanded polystyrene and foamed polyurethane. The importance of density as a characteristic is highlighted by the linear dependence of total heat emission on density for all investigated polymers, making a prediction of thermal loads possible. The peak heat release rate of flame‐retarded EPP and E‐mPPE was found not to be dependent on density, indicating an increased homogeneity by addition of flame retardant.

Moisture uptake in nanocellulose: the effects of relative humidity, temperature and degree of crystallinity

Foams made from cellulose nanomaterials are highly porous and possess excellent mechanical and thermal insulation properties. However, the moisture uptake and hygroscopic properties of these materials need to be better understood for their use in biomedical and bioelectronics applications, in humidity sensing and thermal insulation. In this work, we present a combination of hybrid Grand Canonical Monte Carlo and Molecular Dynamics simulations and experimental measurements to investigate the moisture uptake within nanocellulose foams. To explore the effect of surface modification on moisture uptake we used two types of celluloses, namely TEMPO-oxidized cellulose nanofibrils and carboxymethylated cellulose nanofibrils. We find that the moisture uptake in both the cellulose nanomaterials increases with increasing relative humidity (RH) and decreases with increasing temperature, which is explained using the basic thermodynamic principles. The measured and calculated moisture uptake in amorphous cellulose (for a given RH or temperature) is higher as compared to crystalline cellulose with TEMPO- and CM-modified surfaces. The high water uptake of amorphous cellulose films is related to the formation of water-filled pores with increasing RH. The microscopic insight of water uptake in nanocellulose provided in this study can assist the design and fabrication of high-performance cellulose materials with improved properties for thermal insulation in humid climates or packaging of water sensitive goods.Graphic abstract

Construction and Nanostructure of Chitosan/Nanocellulose Hybrid Aerogels.

Biomass aerogels have received extensive attention due to their unique natural characteristics. However, biomass-based chitosan aerogels are often confronted with the traditional issue concerning a weak skeleton structure, namely, the corresponding huge shrinkage for chitosan aerogels in the stage from the final gel to the aerogel. Herein, we put forward a new approach to enhance chitosan aerogels by introducing natural biomaterial cellulose nanocrystal (CNC). CNC is applied to connect/cross-link chitosan chains to form its networking construction through supramolecular interaction/physical entanglement, eventually realizing the enhancement of the chitosan aerogel network structure. Chitosan aerogels modified with CNC exhibit a high specific surface area of 578.43 cm2 g-1, and the pore size distribution is in the range of 20-60 nm, which is smaller than the mean free path of gas molecules (69 nm), triggering a "no convection" effect. Hence, the gaseous heat transfer of chitosan aerogel is effectively suppressed. Chitosan aerogels with the addition of CNC show an excellent thermal insulation property (0.0272 W m-1 K-1 at ambient condition) and an enhanced compressive strength (0.13 MPa at a strain of 3%). This improvement method of chitosan aerogel in enhancing the skeleton structure aspect provides a new kind of idea for strengthening the nanoscale morphology structure of biomass aerogels.

Seaweed-Derived Alginate-Cellulose Nanofiber Aerogel for Insulation Applications.

The next generation of green insulation materials is being developed to provide safer and more sustainable alternatives to conventional materials. Bio-based cellulose nanofiber (CNF) aerogels offer excellent thermal insulation properties; however, their high flammability restricts their application. In this study, the design concept for the development of a multifunctional and non-toxic insulation material is inspired by the natural composition of seaweed, comprising both alginate and cellulose. The approach includes three steps: first, CNFs were separated from alginate-rich seaweed to obtain a resource-efficient, fully bio-based, and inherently flame-retardant material; second, ice-templating, followed by freeze-drying, was employed to form an anisotropic aerogel for effective insulation; and finally, a simple crosslinking approach was applied to improve the flame-retardant behavior and stability. At a density of 0.015 g cm–3, the lightweight anisotropic aerogels displayed favorable mechanical properties, including a compressive modulus of 370 kPa, high thermal stability, low thermal conductivity (31.5 mW m–1 K–1), considerable flame retardancy (0.053 mm s–1), and self-extinguishing behavior, where the inherent characteristics were considerably improved by crosslinking. Different concentrations of the crosslinker altered the mechanical properties, while the anisotropic structure influenced the mechanical properties, combustion velocity, and to some extent thermal conductivity. Seaweed-derived aerogels possess intrinsic characteristics that could serve as a template for the future development of sustainable high-performance insulation materials.

Preparation of functionalized halloysite reinforced polyimide composite aerogels with excellent thermal insulation properties

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.

Thermal conductivity and electrical insulation properties of h-BN@PDA/silicone rubber composites

In recent years, with the increasing demands of portable and high-speed electronic devices, highly integrated equipment attracts people's attention more and more. However, it is a great challenge to guarantee the long-term stability of electronic products at high temperatures. Hexagon boron nitride (h-BN), which owned excellent thermal conductivity and insulation properties, was preferred for electronics. For better compatibility of inorganic fillers and silicone rubber, a biological modification by coating polydopamine (DA) on h-BN was adopted. Herein, the composites based on h-BN@PDA and silicone rubber were fabricated. Compared with h-BN/silicone rubber composites, the thermal conductivity of h-BN@PDA/silicone rubber composites increased and volume resistance of materials had been decreasing. When the amount of h-BN@PDA fillers was 30 wt%, the thermal conductivity of h-BN@PDA/silicone rubber composite increased to 0.95 W m−1 K−1. The volume resistivity of 30 wt% h-BN@PDA/silicone rubber composite reached 2.5 × 1011 Ω·cm, which was the lowest one among others, which still exceeded requirements of electronic materials.

Ultralight and superelastic polyvinyl alcohol/SiC nanofiber/reduced graphene oxide hybrid foams with excellent thermal insulation and microwave absorption properties

Being in the strategic direction of next-generation absorbers, multifunctional microwave absorbing materials possess great application value in military and commercial fields. However, the stringent requirements for performance necessitate the combination of multiple functions in such type of composites, which is still a challenge. This work aims to develop a foam-type absorber composed of multi-dimensional organic and inorganic materials, in which reduced graphene oxide sheets and polyvinyl alcohol membranes serve as the framework and crosslinker to form a three-dimensional skeleton. Meanwhile, SiC nanofibers as a reinforcing component can effectively suppress the over-stacking of reduced graphene oxide and enhance the conductivity and mechanical strength of cell walls. Among the remarkable microwave absorbing properties of the obtained foam, there are the ultra-light (9.85 mg cm-3), broadband (7.04 GHz), and strong absorption (reflection loss of -61.02 dB), all combined in the ultra-thin (2.5 mm). In addition, the foam possesses superelastic and excellent heat-insulating characteristics that ensure shock resistance, heat preservation, and infrared stealth. The remarkable versatility benefits from the porous structure, as well as from the synergistic effect of multi-dimensional organic and inorganic constituents of the foam. Therefore this study lays the foundation for the design of new-generation microwave absorbers with broad application potential.