Thermal Insulation Applications Research Articles

Silica Aerogel-Rubber Composite: A Sustainable Alternative for Buildings' Thermal Insulation.

Silica aerogel composites with recycled tire rubber have been synthesized and evaluated for their potential use for thermal protection in buildings. The present work describes for the first time the preparation of silica-based aerogel composites containing recycled rubber tires reinforced with polyvinyl butyral (PVB) by hot pressing. The developed composite was extensively characterized regarding its physical, morphological, thermal and mechanical features, and the results showed their properties were relevant, leading to composites with different properties/performances. The obtained bulk density values were satisfactory, down to 474 kg·m−3, and very good thermal properties were achieved, namely, thermal conductivity as low as 55 mW·m−1·K−1 for composites with silica aerogel, recycled tire rubber and PVB. The most promising composites were those based on low bulk density and thermal conductivity values, and they were thermally stable, indicating their suitability for thermal insulation applications.

Aramid Pulp Reinforced Clay Aerogel Composites: Mechanical, Thermal and Combustion Behavior.

In this work, we reported that aramid pulps (AP) reinforced clay aerogel composites with improved mechanical strength, good thermal insulation and fire resistance based on the combination of AP, Poly(vinyl alcohol) (PVA) and sodium montmorillonite (MMT), which present a promising prospect in the thermal insulation application. The PVA-MMT-APx (x: denotes the mass content of AP) aerogel composites present an isotropic “lamella-honeycomb” porous structure, which endows them with excellent comprehensive performance. With the AP content increasing, the extremely low density is kept, ranging between 67–73 mg/cm3, and the low thermal conductivity is maintained within 40.9–47.9 mW·m−1·K−1. The mechanical strength is significantly improved with the maximum compressive modulus increasing from 2.95 to 5.96 MPa and the specific modulus rising from 44.03 to 81.64 MPa∙cm3/g. Their detailed heat transfer process has been analyzed, which provides a deep understanding to the low thermal conductivity of the PVA-MMT-APx aerogel composites. Based on the combination of thermogravimetric analysis and combustion behavior, the PVA-MMT-APx aerogel composites are demonstrated to possess improved thermal stability and fire resistance. This study puts forward a facile approach to utilizing AP to reinforce clay aerogel composites, which provides new insight into the development of thermal-insulating, fire-safe and high-strength thermal insulation materials.

Recyclable and high-performance metal coordination bonds cross-linked polybenzimidazole aerogels for flame retardancy, thermal insulation and dyes adsorption applications

Aerogels made from high-performance polymers have attracted great interests in recent years. However, traditional chemical crosslinking process is complex, and makes it difficult to adjust the skeleton structure of aerogels and achieve polymer recovery. Herein, polybenzimidazole aerogels with good mechanical property, uniform porous structure, and specific surface area as high as 660.23 m2/g are facilely prepared through metal coordination. The excellent thermal stability, high flame resistance, and low thermal conductivity make the aerogels good candidates for flame-retarding and high-temperature thermal insulating materials. Notably, the reversible metal coordination crosslinking permits the recycling of aerogels, which has not been realized in previous high-performance polymer aerogels yet. Moreover, the aerogels can repeatedly adsorb dyes from wastewater because of their large specific surface area, good chemical resistance, and abundant polar imidazole groups. This work is expected to provide a simple approach to recyclable, high-performance, and multifunctional polymer aerogels.

Large-scale synthesis of macroscopic layered inorganic-organic hybrid nanobelt aerogel monoliths with multifunctionality

Fabrication of freestanding nanostructured aerogel monoliths with multifunctionality on a large scale represents a great challenge due to the limited scalable methods for synthesis and assembly of multi-component nanostructures into one single gel body. Here, we report a scalable solvothermal-based in situ gelation method for synthesizing mechanically stable cobalt-based layered inorganic-organic hybrid nanobelt (Co-LIOHN) aerogel monoliths with a density as low as 2.8 mg/cm 3 , an ultralow thermal conductivity of 25 mW/(mK), and extraordinary adsorption capacities of 51–145 g/g for various solvents. Moreover, the aerogel exhibits reversible thermochromic behavior originating from the changing of the coordination environment of the Co 2+ caused by the loss and uptake of coordinating molecular water upon heating and cooling. The Co-LIOHN aerogels integrate unique features of the aerogel and intrinsic properties of the hybrid nanobelts, giving access to a truly multifunctional material that has great potential for applications in thermal insulation, environmental remediation, sensing, and camouflage. • A scalable in situ gelation method is developed for producing Co-LIOHN aerogels • The gelation is enabled by self-crosslinking of nanobelts via van der Waals forces • The Co-LIOHN aerogel shows excellent oil removal and thermal insulation capability • The Co-LIOHN aerogel demonstrates unprecedented thermochromic properties Li et al. report a facile and scalable in situ gelation method for the fabrication of macroscopic freestanding cobalt-based layered inorganic-organic hybrid nanobelt aerogel monoliths that exhibit outstanding oil removal, thermal insulation, and thermochromic properties.

Mechanical and Thermal Properties of Functionally Graded Polyolefin Elastomer Foams.

In this work, uniform and graded polyolefin elastomer (POE) foams were prepared using a single-step technology based on a fixed chemical blowing agent (azodicarbonamide) concentration of 4 phr (parts per hundred rubber). The effect of molding temperature, including the average temperature (Tavg) and temperature difference (ΔT), on the foams’ morphology, mechanical properties (tension, compression and hardness) and thermal conductivity was investigated. Two series of samples were produced by fixing Tavg with different ΔT or setting different ΔT, leading to different Tavg. The morphological analyses showed that two or three regions inside the foams were produced depending on the molding conditions, each region having different cellular structure in terms of cell size, cell density and cell geometry. The results obtained for the conditions tested showed a range of density (0.55–0.72 g/cm3), tensile modulus (0.44–0.70 MPa) and compression elastic modulus (0.35–0.71 MPa), with a thermal conductivity between 0.125 and 0.180 W/m.K. Based on the information provided, it can be concluded that the foam’s properties can be easily controlled by the cellular structure and that graded samples are more interesting than uniform ones, especially for thermal insulation applications, such as packaging, construction, transportation, automotive and aerospace industries.

WITHDRAWN: Lightweight and hydrophobic silica-cellulose composite aerogel based on interpenetrating networks

Silica aerogels are common porous materials with extremely low density, high porosity and low thermal conductivity while plagued by their inherent fragility. Here silica-cellulose composite aerogels with hierarchical porosities are prepared using in situ two-step strategy, wherein the cellulose aerogels derived from the degreasing cotton are used as templates and mediate the assembly of methyltrimethoxysilane (MTMS)/tetraethoxysilane (TEOS) silicon nanoparticles. Silica particles and the cellulose scaffold cross-link with each other via hydrogen bonding, forming an interpenetrating network structure. The presence of cellulose scaffold endows the composite aerogel with low density ( ρ = 0.0711-0.1027 g cm −3 ), superior compressive strength (2.21 MPa high Young's modulus) and outstanding thermal insulation performance ( λ = 0.0344-0.0422 W m −1 K −1 ). Moreover, the Si-CH 3 in MTMS notably increases the hydrophobicity as the water contact angle of the composite aerogels reaches up to 132°. The robust and hydrophobic silica-cellulose composite aerogels can be ideal candidates for thermal insulation applications. The monolithic silica-cellulose composite aerogels prepared using in situ two-step strategy simultaneously integrate reduced thermal conductivity and enhanced hydrophobicity as well as high compressive strength for practical demands.

Mechanical and Thermal Characteristics of Hybrid Composites Fortified with Flax, Banyan, and Glass Fibers for Automobile Safety Applications

ABSTRACT Automobile sector is growing day by day due to the globalization and the urbanization. Further, the luxury life of human beings leads to the new development in the production of automobiles. Consumers are looking for fuel economy with safety features in automobiles. Hence, the weight reduction and strength performance of components play major role in manufacturing of automobiles. In this current investigation, we tried to develop new composite materials with light weight and better thermal and mechanical characteristics using natural and synthetic fibers. Totally, six types of composites were manufactured, namely, Epoxy/Banyan, Epoxy/Glass, Epoxy/Flax, Epoxy/Banyan/Flax, Epoxy/Banyan/Glass, and Epoxy/Flax/Glass by conventional hand layup method by keeping matrix-to-fiber ratio as 60:40. Mechanical and thermal characteristics of the composites were examined. Based on the thermal behavior of composites, Epoxy/Banyan composite was selected as the suitable candidate for thermal insulation applications in automobile industries as exhibited least thermal conductivity of 0.112 W/mK. Further, the mechanical characteristics were tested for Epoxy/Banyan composite. Results displayed the properties as: tensile strength − 75 MPa; flexural strength − 113 MPa; impact strength − 12.8 kJ/m2.

Sustainable thermo-acoustical insulation material from cardboard waste and natural fibers: Elaboration and performance evaluation

The main objective of this paper is to elaborate and characterize new ecological composites based on cardboard waste and abandoned natural fibers, in the Drâa-Tafilalet region (South-East, Morocco), for the manufacture of local thermo-acoustical insulation panels. For this study, 25 samples were prepared by mixing 60% of cardboard waste and 40% of vegetable fibers (Reed tree, esparto fiber, fig tree, and Olive tree). The morphological analysis of the different fibers was carried out by scanning electron microscopy (SEM), while, the physical, thermal, and acoustical properties of samples were measured experimentally using standard methods. The experimental results showed that all new composites have better thermal and acoustical performances comparable to those of synthetic insulation materials. The density, thermal conductivity, thermal diffusivity, and sound absorption coefficient of those composites were in the range of 278.6–343.8 kg/m3; 0.072–0.10 W/m·K; 1254.5–1807.5 J/kg·K; 0.4–0.8, respectively. Consequently, the by-products recovered in this study are good candidates for the development of local insulation materials with useful properties for thermal and acoustical insulation applications in buildings, low environmental impact, low cost, and competition with commercialized synthetic insulation materials.

Performance Evaluation of Natural Composites Made from Banyan and Cotton Fibers for Sustainable Thermal Insulation Applications

ABSTRACT Natural composites are gaining more attention due to the light weight and low cost characteristics. In the present investigation, an attempt has been made to fabricate the natural composites using natural fibers like Banyan and Cotton. Composites were made by compression molding technique and five types of composites were prepared, namely, B, BC(3:1), BC(1:1), BC(1:3) and C. Mechanical and thermal properties of the composites were tested. Results showed that Banyan composite exhibited the maximum tensile and flexural strength of 75 MPa and 113 MPa, respectively. This was attributed by the placing of high strength and stiffness Banyan fiber. Further, a maximum thermal resistance of 18.1 × 10−3 m2K/W was observed for Banyan composite. Moreover, the Banyan composite displayed the least coefficient of thermal expansion (CTE) of 1.81 × 10−5/°C which indicated the good dimensional stability of composite. Furthermore, a high thermal diffusivity of 8.79 × 10−7 m2/s was achieved for Banyan composites. Based on the experimental results, it is suggested that the Banyan composite could be a suitable candidate for sustainable thermal insulation applications.

The Role and Applications of Aerogels in Textiles

Textiles have been used for clothing purposes since ancient times. However, due to their functional properties, their importance—as well as their use in various fields such as filtration, protective clothing, and medical applications—increased over time. Properties of the textile fabrics depend mostly on the fiber type, fabrication technique, and structure. Moreover, fabric porosity is one of the properties that provide comfort, increased thermal insulation, and filtration capability to the end products. The porous structure of woven, knitted, and nonwoven fabrics has been used for many years to get the desired porosity. Usually, macroporous structures are achieved using these types of textiles. Electrospinning is used to produce nanoporous textile fibrous web, but its poor mechanical properties and low production rate limit its use. Aerogels are solid materials with ultrahigh porosity at the nanoscale with low density and good thermal insulation properties, due to which they are considered potential insulation materials today. On the other hand, pure aerogels are sometimes brittle and have poor mechanical properties. Thus, they cannot be directly used in various applications. Consequently, textile reinforced aerogel composites have been developed, which could provide flexibility and strength to aerogels and impart nanoporous structure to textiles. This review summarizes conventional techniques to produce the porous structure in textiles followed by the modern techniques to develop a nanoporous structure. Further, different mechanisms to synthesize textile reinforced aerogel composites are discussed to get a nanoporous structure for filtration and thermal insulation applications. The porosity, mechanical properties, and thermal insulation of textile reinforced aerogel composites are also highlighted. In the end, we give a conclusion that not only summarizes the literature, but also includes recommendations for the researchers.

Self-Modulation-Guided Growth of 2D Tellurides with Ultralow Thermal Conductivity.

Ultralow thermal conductivity materials have triggered much interest due to diverse applications in thermal insulation, thermal barrier coating, and especially thermoelectrics.Two dimensional (2D)indium tellurides with ultralow thermal conductivity provide a versatile platform for tailoring the heat transfer, exploring new candidates for thermoelectrics, and achieving miniature, lightweight, and highly integrated devices. Unfortunately, their nanostructure and structure-related heat transfer properties at a 2D scale are much less studied due to difficulties in material fabrication. The ionic character between interlayers and strong covalent bonds in 3D directions impede the anisotropic growth of indium telluride flakes; meanwhile, the low environmental stability and chemical reactivity of tellurium also limit the fabrication of high-quality tellurides, thus hindering the exploration of thermal transport properties. Here, a self-modulation-guided growth strategy to synthesize high-quality 2D In4 Te3 single crystals with ultralow thermal conductivity (0.47Wm-1 K-1 ) is developed. This strategy can also be extended to synthesize a series of highly crystallized metal tellurides, providing excellent candidates for further application in thermoelectrics.

Thermal insulative 2D-oriented bimodal micro-foams and high strength photonic thermoplastic elastomers by assembling olefin multiblock copolymers

Hierarchical 2D-oriented micro-foams and photonic elastomers are produced by assembling the mesophase separated and crystallized superstructures of olefin multiblock copolymers (OBCs). Highly 2D-oriented monomodal and bimodal micro-foams are prepared via compression molding of as-received nascent OBC pellets, irradiation crosslinking, and a subsequent moderate-to-high-pressure supercritical CO2 foaming. Randomly short range ordered bimodal micro-foams are generated from the sheared counterparts. These micro-foams show excellent lightweight properties with foam density of 0.061–0.188 g cm−3 and outstanding thermal conductivity of 20–36 mW m−1 K−1 by laser flash analysis. Moreover, the order-disorder and order-order transitions of nascent and sheared bulk OBCs are characterized by a sequential annealing and subsequent crystallization procedure. The self-seeded nascent and sheared OBCs show hierarchical mesophase separation with domain spacings of 80–258 nm, measured by ultra-small X-ray scattering. The selective visible-light transmitted, transparent, and high-strength thermoplastic elastomers are then made via solvent-free compression molding of these OBC pellets. Meanwhile, low-temperature Sc-CO2 foaming shows that 2D lamellar crystals and 2D, 3D-growing spherulitic crystals with sharp interfaces are individually organized within 2D-oriented lamellar domains of photonic and opaque sheets, which account for their high tensile strength and low strain hardening properties, respectively. The 2D-oriented bimodal micro-foams and assembled photonic elastomers possess potential applications in lightweight sound and thermal insulation, auto-parts, shape memory light actuators, and soft sensors.

Thermal driven self-healing infrared and heat shielding composites based on reversible Diels-Alder reaction

Infrared and heat shielding materials have a wide range of applications in military infrared invisibility and thermal insulation for energy saving, but mechanical damage during use may reduce the service life. In this study, waterborne polyurethanes/gallium tin oxide (WPU/GTO) composites with good infrared and thermal shielding capabilities were fabricated after the introduction of GTO nanoparticles into the thermal driven self-healing WPU matrix. The results showed that the WPU/GTO composite films can show good healing efficiency through thermally reversible DA reactions, with a self-healing efficiency of 80 % in 30 min at 120 °C. In addition, the presence of GTO gives the composite good thermal shielding properties without affecting its thermal stability. Due to free carrier absorption and plasma reflection, the resulting composite films containing 1 wt% GTO could shield from approximately 95 % of infrared light, with an insulation temperature difference of 15 °C when compared to pure polyurethane. This work provides a feasible solution for the preparation of infrared and heat shielding materials with self-healing capabilities.

Improved mechanical strength and thermal resistance of porous SiC ceramics with gradient pore sizes

Thermal insulation applications of porous SiC ceramics require low thermal conductivity and high mechanical strength. However, low thermal conductivity and high mechanical strength possess a trade-off relationship, because improving the mechanical strength requires decreasing the porosity, which increases the thermal conductivity. In this study, we established a new strategy for improving both the mechanical strengths and thermal resistances of porous SiC ceramics with micron-sized pores by applying a double-layer coating with successively decreasing pore sizes (submicron- and nano-sized pores). This resulted in a unique gradient pore structure. The double-layer coating increased the flexural strengths and decreased the thermal conductivities of the porous SiC ceramics by 24–70 % and 29–49 % depending on the porosity (48–62 %), improving both their mechanical strengths and thermal resistances. This strategy may be applicable to other porous ceramics for thermal insulation applications.

New Composite Materials Made from Rigid/Flexible Polyurethane Foams with Fir Sawdust: Acoustic and Thermal Behavior.

The aim of this work is to obtain new materials with improved sound absorbing and thermal properties, using rigid or flexible polyurethane foam reinforced with recycled fir sawdust from wood processing as well as by optimizing their mixing ratio. In this respect, we prepared and characterized samples by mixing rigid polyurethane foam (RPUF)/flexible polyurethane foam (FPUF) with 0, 35, 40, 45, and 50 wt% fir sawdust (FS) with grains size larger than 2 mm. The samples were evaluated by cell morphology analysis, sound absorption, and thermal insulation performance. The obtained composite materials containing 50% sawdust have superior acoustic properties compared to those with 100% FPUF in the range of 420–1250 Hz. The addition of 35% and 50% FS in the FPUF matrix led to improved thermal insulation properties and decreased thermal insulation properties in the case of RPUF. The results show that the use of FS-based composites with the FPUF/RPUF matrix for sound absorption and thermal insulation applications is a desirable choice and could be applied as an alternative to conventional synthetic fiber-based materials and as a recycling method of waste wood.

Preparation of high closed porosity foamed ceramics from coal gangue waste for thermal insulation applications

Resource utilization of industrial solid waste can be a preferred solution to waste management. This study proposes a new strategy to prepare high closed porosity foamed ceramic with coal gangue waste as the major material. The chemical composition and crystalline phase of the starting material, formation mechanism and the effects of sintering process parameters on the pore structure and properties of the samples are discussed. The results show that the density, compressive strength, and true porosity of the foamed ceramic are 0.22 g/cm3, 1.51 MPa, 91.38%, respectively, at the optimum sintering temperature and time of 1200 °C and 30 min. The high closed porosity of 83.95% compared to conventional foamed ceramics is a very favorable factor for the reduction of thermal conductivity and water absorption, resulting in a low of 0.11 W/(m·K) and 0.68%, respectively, which can be used as a cost-effective inorganic thermal insulation material in the building industry.

Hierarchically porous and highly transparent polymethylsilsesquioxane aerogels with an ultrahigh specific surface area using an organic alkali as a catalyst, surfactant, and template

A hierarchically porous aerogel with an ultrahigh specific surface area, high visible light transmittance, excellent mechanical properties, and cubic shell-shaped pores was obtained using a supercritical drying process. Ethanol and methyltriethoxysilane (MTES) were used as a solvent and silicon source, respectively, whereas tetramethylammonium hydroxide (TMAOH) acted as a basic catalyst, surfactant, and template. The phase separation during gelation was finely adjusted by changing the ethanol-to-water ratio to control the gel skeleton structure, the number of crystallization templates, and the light transmittance of the aerogel. The hierarchical porous aerogels exhibited a uniform three-dimensional network. Notably, the specific surface area of the aerogels was 909 m2/g, the visible light transmittance was 58.1%, the hydrophobic angle was 166.5°, the thermal conductivity was 18.2 mW/(m·K), and the stress was 0.301 MPa at 50% compressive strain. The unique structure and excellent performance of the hierarchical porous aerogels make them promising for thermal and sound insulation applications. Moreover, the innovative use of TMAOH as a surfactant and template can be inspiring for the preparation of polymer-reinforced or highly crosslinked aerogels.

Additively Manufactured Nested and Non-Nested Cellular Solids for Effective Stress Distribution and Thermal Insulation Applications: An Experimental and Finite Element Analysis Study

In this study, the design, additive manufacturing and experimental as well as simulation investigation of mechanical and thermal properties of cellular solids are addressed. For this, two cellular solids having nested and non-nested structures are designed and additively manufactured via laser powder bed fusion. The primary objective is to design cellular solids which absorb a significant amount of energy upon impact loading without transmitting a high amount of stress into the cellular solids. Therefore, compression testing of the two cellular solids is performed. The nested and non-nested cellular solids show similar energy absorption properties; however, the nested cellular solid transmits a lower amount of stress in the cellular structure compared to the non-nested cellular solid. The experimentally measured strain (by DIC) in the interior region of the nested cellular solid is lower despite a higher value of externally imposed compressive strain. The second objective of this study is to determine the thermal insulation properties of cellular solids. For measuring the thermal insulation properties, the samples are placed on a hot plate; and the surface temperature distribution is measured by an infrared camera. The thermal insulating performance of both cellular types is sufficient for temperatures exceeding 100 °C. However, the thermal insulating performance of a non-nested cellular solid is slightly better than that of the nested cellular solid. Additional thermal simulations predict a relatively higher temperature distribution on the cellular solid surfaces compared to experimental results. The simulated residual stress shows a similar distribution for both types, but the magnitude of residual stress is different for the cellular solids upon cooling from different temperatures of the hot plate.

Flexible and compressive Al2O3/ZrO2/Y2O3 nanofibrous membranes for thermal insulation at 1400 °C

Ceramic nanofibrous membranes are used in thermal insulation and various applications. However, ceramic nanofibrous materials were rigid and brittle during high temperatures, leading to structural collapse and limited crystallographic slips. Developing flexible and compressive ceramic materials were necessary but challenging. Herein, we set the flexible and compressive Al2O3/ZrO2/Y2O3 nanofibrous membranes using sol-gel electrospinning and sintering. The Al2O3/ZrO2/Y2O3 nanofibrous membranes at −196 °C to 1400 °C could maintain flexibility and compressive performance. These multiple favorable merits presented the nanofibrous membranes for thermal insulation in new energy batteries, aeronautics, automobile, and even under harsh conditions.

(AlCrMg)x(PO4)y/MgO composite: A new thermal protection and insulation material up to 2400 °C

A (AlCrMg)x(PO4)y/MgO composite(APMC) was prepared based on the acid–base reaction between MgO and chromium aluminum phosphate solution for thermal protection and insulation applications at ultrahigh-temperatures up to 2400 °C. The compositions, formation mechanisms, microstructure, mechanical properties, thermal conductivity and ablation resistance of the composite were systematically investigated. The results show that the (AlCrMg)x(PO4)y/MgO composite can be consolidated in different shapes at room temperature. The compressive strength of the as-prepared porous composites is higher than 20 MPa due to the macromolecular network structure, and it can be further improved to 42 MPa via thermal treatment. After ablation by an oxyacetylene flame at 2400 ± 70 °C for 60 s, the mass and line ablation rates of the composite were 0.0195 g/s and 0.43 × 10−3 mm/s, respectively, which are comparable to those of ultrahigh-temperature ceramics. The excellent ablation resistance can be attributed to the in situ formation of a dense protective layer composed of spinel MgCr2O4 and MgO phases. Interestingly, during ablation at 2400 °C the back-side temperature of the 15 mm-thick sample was lower than 130 °C, suggesting outstanding thermal insulation performance. The temperature gradient leads to the formation of a gradated porous structure which reduces the overall thermal conductivity of the composite.