Aerogel Content Research Articles

Thermal Insulation Performance of Cotton and PET-based Hybrid Fabrics Impregnated with Silica Aerogel via a Facile Dip-dry Process

We report the morphological features and thermal insulation properties of a series of cotton- and PET-based hybrid fabrics impregnated with silica aerogel. For the purpose, commercially available cotton and PET knitted fabrics were dipped into aqueous dispersions including different silica aerogel contents, dried, and stacked to 1, 3, and 5 layers. The SEM images revealed that the silica aerogel particles were well incorporated into cotton or PET knitted fabrics. The thermal insulating performance of the hybrid fabrics as functions of the silica aerogel content and the number of layers of stacked fabrics were characterized by monitoring the surface temperatures of the fabrics on a plate with a wide temperature range of ~50-80 oC using an infrared camera. The higher thermal insulation performance was attained for both cotton- and PET-based hybrid fabrics with higher silica aerogel contents. In addition, 3-layered hybrid fabrics exhibited noticeably improved thermal insulation performance, compared to 1- or 5-layered fabrics. The thermal insulation property of the cotton-based hybrid fabrics was dominantly influenced by silica aerogel than that of PET-based hybrid fabrics. The overall results demonstrated that the cotton- and PET-based hybrid fabrics with silica aerogel manufactured by a facile dip-dry process could be utilized as protective garments, heat-sensitive devices, pipes, automotive, aircrafts, and buildings for thermal insulation applications.

Evaluation of silica aerogel-reinforced polyurethane foams for footwear applications

In this work, a simple way to create a nanocellular structure within polyurethane (PU) foam was developed by the incorporation of silica aerogels, and the resultant foams were evaluated for footwear applications. To protect the brittle aerogels from breakage, the softness of PU foams was first tailored by changing the ratio of glycerol and polypropylene glycol. Different amounts of silica aerogels (0–15 wt%) were then loaded into a selected PU foam and analyzed in terms of compressive mechanical properties, shock attenuation performance, and thermal insulation. After incorporation of the aerogels, the compressive modulus, the compressive stress, and the deformation recovery of the foams improved, while the excellent flexibility was preserved. For simulated gait experiments, the shock attenuation capability of the foams was shown to increase with an increase in the aerogel content. These findings can probably be attributed to the improved elasticity of the solid phase and the changed morphology of the gaseous phase as observed from the SEM images. Moreover, the thermal insulation of the developed foams was also investigated, showing an increased trend with the aerogel content.

Fabrication and characterization of Aerogel-Polydimethyl siloxane (PDMS) Insulation Film

The building has a large impact on the space heating demand and the indoor environment is affected by climate or daylight. Hence, silica aerogel has generally used as a film to reduce the coefficient of the window in the building. Silica aerogel is a suitable material to apply for insulation material with lower thermal conductivity than that of air to save interior energy. However expensive precursor and drying process were the main issue of the silica aerogel synthesis and practical usage. We attempt to fabricate aerogel insulation film for energy saving through the economic process under ambient pressure. Silica aerogel was synthesized from rice husk ash, which was an agricultural waste to be able to recycle. Taguchi design was used to optimize the parameters (amount of rice husk ash, pH, aging time) controlling the surface area of silica aerogel. The silica aerogel is prepared by sol-gel processing through acidic treatment and aging. The silica aerogel was obtained by modification of silica hydrogel surface and dry at ambient pressure. Finally, aerogel film was respectively fabricated by the different content of aerogel in polydimethylsiloxane (PDMS). Silica aerogel obtained 21 – 24nm average particle size was analyzed by SEM and silica aerogel with high surface area (832.26 m2/g), pore size ( 3.30nm ) was characterized by BET. Then silica Aerogel – PDMS insulation film with thermal conductivity (0.002 W/mK) was analyzed by thermal wave system. The study demonstrates an eco-friendly and low-cost route toward silica – PDMS insulation film with low thermal conductivity (0.002 W/mK).

Heat insulating, fire retardant and flexible inorganic nanocomposite paper

Organic heat insulating materials with low density and low thermal conductivity have been widely used in building and domestic appliances. However, their highly flammable and poorly flexible characteristics hamper the application under certain circumstances. In this work, novel nanocomposite paper with low thermal conductivity, flame retardancy and good mechanical property was prepared by employing ultralong hydroxyapatite (HAP) nanowires as scaffolds for silica aerogels. The conductivity of the HAP/silica aerogel nanocomposite paper at room temperature decreased from 0.056 to 0.045Wm−1K−1 as the amounts of silica aerogels increased from 0 to 50wt%, indicating the excellent heat insulating performance. Meanwhile, the prepared paper showed remarkable flame retardancy with the peak heat release rate (HRR) of only 33.1W/g when silica aerogel content was 50wt%. Thermal stability analysis showed that the weight losses of all the nanocomposite papers with different contents of silica aerogels were <10wt% even at 800°C, which showed that the nanocomposite paper possessed prominent thermal stability. Besides, the nanocomposite paper exhibited good mechanical property. Therefore, the as-prepared HAP/silica aerogel nanocomposite paper is promising for applications in the protection layer of insulation materials, fire-retardant wallpaper, specialty fire clothing, and so on.

Fabrication of silica aerogel composite blankets from an aqueous silica aerogel slurry

Low-density silica aerogel composite blankets were successfully fabricated from silica aerogel slurries via an impregnation technique. Silica aerogel powder formed a stable slurry in a mixed ethanol/water solution with a polyvinyl alcohol (PVA) binder. Scanning electron microscopy (SEM) images indicated that the silica aerogel particles maintained their mesoporous and three-dimensional microstructure upon evaporation of the solvent. The obtained silica aerogel composite blankets had low densities (0.13gcm−3), high silica aerogel contents (79%), and low thermal conductivities (18.92mWm−1K−1) compared to those of the polyethylene (PE) blanket.

Mechanical, thermal, and hydrophobic properties of silica aerogel–epoxy composites

ABSTRACTEpoxy composites were prepared with different contents of hydrophobic silica aerogel particles to investigate their mechanical, thermal, and hydrophobic properties. The composites, particularly the one containing 1 wt % silica aerogel, showed remarkable toughness and yielding behaviors compared to neat epoxy, with its brittle behavior. As the content of silica aerogel increased, the thermal properties of the composites (e.g., thermal conductivity and thermal stability) improved. This was due to the very low thermal conductivity and high thermal stability of the silica aerogel particles. Moreover, the use of the hydrophobic silica aerogel led to the development of composites with hydrophobic properties. To examine the hydrophobicity more deeply, a series of water‐uptake tests were performed, and the results show that the composite with 3 wt % silica aerogel absorbed 50% less water than the neat epoxy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45706.

In-situ synthesis of silica aerogel in polyethylene terephthalate fibre nonwovens and their composite properties on acoustical absorption behavior

In this research work we focus on engineering the silica aerogel/polyethylene terephthalate (PET) fibre nonwoven fabric composites with various silica content during in-situ synthesis of silica aerogels in the nonwovens and their composite properties on sound absorption. The silica content was varied by varying the molar ratio of methanol (MeOH)/tetraethyl orthosilicate (TEOS) from 110 to 28. The gelation of silica alcogel took place inside the fabric followed by silylation and atmospheric pressure drying. The aerogel/PET nonwoven composites were characterized by FTIR, TGA and contact angle to explain the aerogel content and its behavior. Moreover, the physical properties such as thickness, bulk density, specific airflow resistance, and mean flow pore size have been investigated. The two microphone transfer function method was used to test the sound absorption coefficient (SAC) of aerogel composites at 1/3rd octave frequencies of 50–6300 Hz. The aerogel/PET nonwoven composites have exhibited higher SAC than the untreated or control PET nonwoven for the entire frequency range. The suitable solvent molar ratio of 55 has been recommended for synthesis of silica aerogels by considering not only the silica content to have high sound absorption but also based on hydrophobic characteristics of aerogel/PET nonwoven composites.

Synthesis and characterization of silica aerogel reinforced rigid polyurethane foam for thermal insulation application

This study reports the synthesis of silica aerogel/rigid polyurethane foam nanocomposite with efficient thermal insulation properties. Nanocomposite were prepared in two different states: 1. Adding silica aerogel to MDI matrix, and 2. Adding silica aerogel to polyol matrix by using of various weight percentages of silica aerogel (1–5wt.%). Many techniques were used in order to investigate the effects of silica aerogel on the mechanical, structural, hydrophobic and thermal properties of the nanocomposites. FTIR observations confirmed the reaction between the silica aerogel and MDI matrix, while no reaction was observed between the silica aerogel and polyol matrix. The datum of thermal conductivity and water-contact angle analyses showed that by increasing the silica aerogel content from 0 to 5wt.%, the thermal conductivity of the cyclopentane blown foams were lowered from 0.0314 to 0.0268W/(mK) and hydrophobicity values were increased up to about 24.14% (from 72.13° to 89.57°). However, from the results of mechanical properties, it was concluded that when the silica aerogel content reached 3wt.%, the module and yield stress of foams were enhanced by 18.63% and 13.83%, respectively and then, they were declined by increasing the silica aerogel content. The cell morphology also revealed the same trend.

Microstructural, mechanical, and thermal‐insulation properties of poly(methyl methacrylate)/silica aerogel bimodal cellular foams

ABSTRACTNovel poly(methyl methacrylate) (PMMA)/silica aerogel bimodal cellular foams were prepared by melt mixing and a supercritical carbon dioxide foaming process. The effects of the silica aerogel content on the morphologies and thermal‐insulating and mechanical properties of the foams were investigated by scanning electron microscopy, mechanical tests, and heat‐transfer analysis. The experimental results show that compared to the pure PMMA foam, the PMMA/silica aerogel microcellular foams exhibited more uniform cell structures, decreased cell sizes, and increased cell densities (the densities of the foams were 0.38–0.45 g/cm3). In particular, a considerable number of original nanometric cells (ca. 50 nm) were evenly embedded in the cell walls and on the inner surfaces of the micrometric cells (&lt;10 μm). A 62.7% decrease in the thermal conductivity (0.072 W m−1 K−1) in comparison to that of raw PMMA after 0.5 wt % silica aerogel was added was obtained. Mechanical analysis of the PMMA/silica aerogel foams with 5 and 2 wt % silica aerogel showed that the compressive and flexural strengths were distinctly improved by 92 and 52%, respectively, and the dynamic storage moduli increased. The enhanced performance showed that with the addition of silica aerogel into PMMA, one can obtain thermal‐insulation materials with a favorable mechanical strength. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44434.

Effects of silica aerogel content on microstructural and mechanical properties of poly(methyl methacrylate)/silica aerogel dual-scale cellular foams processed in supercritical carbon dioxide

A novel poly(methyl-methacrylate)/silica aerogel (PMMA/SA) dual-scale cellular foam was synthesized with internal mixing followed by the supercritical carbon dioxide foaming process. The effects of silica aerogel content on the microstructural and mechanical performance of the foams were investigated by SEM, TEM analysis, and mechanical tests. The experimental results suggest that the employment of silica aerogel granule as addictive can distinctly improve the morphological feature as well as the mechanical performance in comparison to neat PMMA foam by uniformizing cell size distribution, decreasing cell size and increasing cell density. And dual-scale cells including micrometric cells of 3-10 μm and nanometric cells of about 50nm existed in the structure of foams resulting from the retained original framework structure of silica aerogel, which has not been described in other studies with the addition of various fillers. Furthermore, the mechanical strength was significantly elevated even with a small amount of silica aerogel resulting from the unique microstructure, decreased cell size and enhanced cell walls. The compressive strength was 18.12 MPa and the flexural strength was 18.90 MPa by adding 5wt% and 2wt% silica aerogel, respectively. These results demonstrate the potential to synthesize PMMA/SA dual-scale cellular foams to be used as structural materials with the advantages of low density and high strength.

Thermal insulation material based on SiO2 aerogel

SiO2 aerogel is a solid material with three-dimensional network structure, has a very low density and low thermal conductivity, can be used as a kind of high efficient heat preservation and heat insulation material, as well as SiO2 aerogel particles. In this work, we have successfully prepared a mortar with SiO2 aerogel particles. Density, mechanical properties, softening coefficient, autogenous shrinkage, antifreeze performance and thermal conductivity properties were studied when the SiO2 aerogel particles replacement ratio was 10%, 20%, 30%, 40%, 50% and 60%. The mortar based on SiO2 aerogel particles shows a density of ∼1.2g/cm3, a compressive strength and flexural tensile strength of ∼2.15MPa and ∼0.45MPa, a thermal conductivity of ∼0.1524W/m·K at the aerogel content of 60vol.%. And on this basis, the thermal conductivity was focused on study when fiber, air-entraining agent and powder were added into the mortar. The results show that when the dosage was 0.2%, 0.05% and 1% respectively, the thermal conductivity was the lowest (0.0859W/m·K).

Silica-based aerogels as aggregates for cement-based thermal renders

Subcritically dried silica-based aerogels were synthesized by design to be used as aggregates for lightweight cement-based thermal renders. The molecular and pore structure of the aerogels and of the corresponding renders were correlated with their thermal conductivities. A subcritical hybrid aerogel proved to have advantages over a supercritical commercial one, since the particle size distribution may be controlled, it is more hydrophobic, and imparts higher specific surface areas and total pore volumes to the renders. Good stabilization of the hybrid aerogels within the aqueous cement paste, without affecting the final renders’ structure, was accomplished by using an anionic surfactant. The efficient range of aerogel contents for thermal insulation purposes (above 60 vol% of total aggregate) was optimized using an inorganic subcritical aerogel. Thermal conductivities as low as ∼0.085 W.m−1.K−1 and densities of 410 kg.m−3 were achieved by total replacement of silica sand with a designed hybrid aerogel.

Synthesis of mesoporous SiO2 aerogel/WxTiO2 nanocomposites with high adsorptivity and photocatalytic activity

Mesoporous SiO2 aerogel/WxTiO2 nanocomposites with high adsorptivity and photocatalytic activity were prepared by hydrothermal deposition method using SiO2 aerogel as carrier. The morphology and microstructure of the SiO2 aerogel/WxTiO2 nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2 adsorption measurements. The results indicated that the SiO2 aerogel/WxTiO2 nanocomposites exhibited sponge-like network-structure with higher pore volume and anatase TiO2 crystallinity. Increasing the SiO2 aerogel content and ethanol/water volume ratio in the precursor solution is favorable for improving the specific surface area and pore volume of SiO2 aerogel/WxTiO2 composite particles. Under the conditions of Si/Ti mol ratio >0.6 and ethanol/water volume ratio >1:3, the specific surface area and pore volume of the as-prepared SiO2 aerogel/WxTiO2 nanocomposites could attain to 195.7–271.3m2/g and 0.86–1.11mL/g, respectively. Moreover, the as-prepared SiO2 aerogel/WxTiO2 nanocomposites exhibited higher adsorptivity and photocatalytic activity. Particularly, the synthesized SiO2 aerogel/WxTiO2 nanocomposite sample 0.9STW-1:3 (Vethanol/Vwater=1/3) exhibited highest efficiency for removing the Rhodamine B in the simulated wastewater. In addition, the as-prepared SiO2 aerogel/WxTiO2 composites still exhibited higher adsorption efficiency and photocatalytic activity after 4 cycles.

Green lightweight cementitious composite incorporating aerogels and fly ash cenospheres – Mechanical and thermal insulating properties

The research focused on the development of an ultra-lightweight cementitious composite with both excellent mechanical and thermal insulating properties. Fly ash cenosphere (FAC), and aerogel, a nano-structured highly porous material made of silica, were used as lightweight aggregates. Polyvinyl alcohol fibers were used to improve the mechanical behavior of the cementitious composite. The experimental results showed higher specific strength (up to 18kPa/kgm−3) of the resulting composites as compared to conventional lightweight materials. Depending on the amount of FAC and aerogel, the compressive and flexural strengths of the cementitious composite were found as 23.54–18.63MPa and 4.94–3.66MPa, respectively, while the thermal conductivity was reduced to 0.3197W/m-K. Moreover, the hydration products and microstructures of the FAC/aerogel modified cementitious composite were investigated by the Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy (EDS). Thermal stability of the hardened matrix was studied by using thermo-gravimetric analyses and it was revealed that the composites were fairly stable at a high temperature range. The weight loss varied with increasing aerogel content. In conclusion, both FAC and aerogel are excellent candidates for producing mechanically strong as well as thermally insulated composites which have great potential to be used in buildings for energy conservation.

The effect of the nano-structured aerogel powder on the structural parameters, water repellency, and water vapor/air permeability of a fibrous polyester material

A water-glass-based silica aerogel was synthesized through an ambient pressure drying method and its structural parameters, hydrophobic property, and blending with a nanofibrous polyester material were investigated. The hybrid aerogel-fibrous materials were prepared using an electrospinning method and their hydrophobic and water vapor/air permeation characteristics were analyzed using the SPSS software by one-way ANOVA, Duncan, and 1-sample K-S tests. The BET and BJH analyses showed that the nanosilica aerogel has a pore size of 24 nm and a total pore volume of 3.5 m3/g resulted in 88.6% porosity and 0.2 g/m3 density. The silica aerogel granules showed a high water sliding angle, whereas, the aerogel powder-coated water droplets (marbles) showed a sliding angle of as low as 5°. The SEM and AFM analyses indicated the successful embedding of the aerogel powder into the nanofibrous material with an irregular beads–like structure. The most aerogel content of 4 wt% in the hybrid fibrous material showed a lower mean diameter (176.2 nm) as well as a lower mean size of spaces formed between the super-fine fibers (3598.5 nm) in comparison with the fibrous material with no aerogel content. The beaded fibrous structures of the hybrid fibrous materials led to a suitable two-scale surface roughness with an improved water contact angle up to 130.1° in comparison with 103.4° for the one with no aerogel content. The samples surface energy was remained unchanged with 3 M water repellency of 1. Also, there was no significant difference between the water vapor permeability (WVP) of the samples according to the ANOVA tests with P-values of more than 0.05. The super-fine fibers containing 2 and 4% aerogel have a higher permeability to air in comparison to the pure super-fine fibers and the super-fine fibers containing 0.5 and 1% aerogel, which may be due to the recognized effect on the reduction of the fibers diameter as well as smaller empty spaces formed between the super-fine fibers.

An Investigation on the Effect of Silica Aerogel Content on Thermal and Mechanical Properties of Sisal/PLA Nano Composites

In this research work, the authors proposed to prepare sisal/poly(lactic acid) (PLA) composites with various amounts of silica aerogel (SAG) particles and studied the effect of aerogel content on the mechanical properties and thermal properties. Characterization of the composites in the presence and absence of aerogel particles were studied by Differential scanning calorimeter and Thermogravimetric analysis analysis. The dispersion trend of SAG particles and interfacial adhesion between the matrix and fibers were assessed by Scanning Electron Microscope (SEM) micrographs of the surface and fractured surface of the composites, respectively. The thermal degradation temperatures of PLA/Sisal composites were increased by compounding with SAG particle. The tensile strength, flexural strength, modulus and water sorption increased with SAG content in the range of 0 to 2 wt%. However, NaOH (5 wt%) treated sisal fiber nanocomposites imparts superior mechanical properties than those of untreated ones. The fracture surface morphologies showed that the SAG particles are uniformly dispersed in PLA matrix. The results obtained by SEM confirmed that the interfacial adhesion between SAG and PLA matrix was good. Biodegradation studies were also performed to study the effect of SAG particles on degradation rate of the composites. Results indicated that the addition of SAG particles improved the overall performance of the composites including their thermal stability and mechanical properties. This work provides us the exploratory idea of using SAG particles as additives in biodegradable composites for possible applications, such as interior parts of automobiles and marine industry etc. POLYM. COMPOS., 39:835–840, 2018. © 2016 Society of Plastics Engineers

Novel lightweight and highly thermally insulative silica aerogel-doped poly(vinyl chloride)-coated fabric composite

Novel lightweight and highly thermal insulative aerogel-doped poly(vinyl chloride)-coated fabric composites were prepared on woven fabrics made of polyester fibres using knife coating method, and their performances were compared with neat composite. The composites were prepared by incorporating a commercial aerogel to a ‘green’ poly(vinyl chloride) (PVC) plastisol. The effect of aerogel-content, thermal insulating property, thermal degradation, surface characteristics, tensile and physical properties of the composites were investigated. Results revealed that aerogel could reduce thermal conductivity, density and hydrophilicity of the composites dramatically without significant decrease in other properties. Experimental results showed that thermal insulation properties were enhanced by ∼26% (from 205 to 152 mW/m-K), density decreased by ∼17% (from 1.132 to 0.941 g/cm3) and hydrophobicity increased by 16.4% (from 76.02 to 88.67 ± 1.48°) with respect to the unmodified coated fabric. Analyses proved that composite with 3% aerogel is the lightest by weight, while 4% showed the highest thermal insulation. The results showed that 4% is the critical percentage, and preparation of composites with aerogel content higher than 4% has limitations with the given formulation due to high viscosity of plastisol. The prepared composite has potential applications in many fields such as development of textile bioreactors for ethanol/biogas production from waste materials, temporary houses and tents, facade coverings, container linings and tarpaulins. The prepared composite can be considered ‘green’ due to usage of a non-phthalate environment-friendly plasticiser.

Fabrication and Characterization of Aramid/Aerogel Composite

The LiCl/DMAc was used as solvent system to dissolve meta-aramid short fiber, the aramid fibrid was prepared by injecting the aramid solution into the high shearing coagulant at room temperature and the mixture of water and N, N-dimethylacetamide (DMAc) was used as coagulant. The aramid fibrid and aramid short fiber were mixed at differents weight proportion, wet paper was dried and aramid paper was prepared by heat pressing. The aramid paper has excellent mechanical properties when the weight proportion of the aramid fibrid and aramid short fiber was 60:40,and it had a good thermal bonding between the fibrid and fiber under heat pressing. The hydrophobic SiO2 was mixed with aramid fibrid and aramid short fiber (60:40) in ethanol, and aramid/aerogel composite was prepared by drying and hot compressing. The composite had a good heat-resisting, however, the mechanical property decreased with the content of aerogel increasing.

Mechanical properties and toughness of carbon aerogel/epoxy polymer composites

Because of their nanoporous structure and large surface area, carbon aerogels have high potential for improving the material properties of polymer-based composites. In the present study, the mechanical properties and toughness of epoxy polymers modified with an aerogel content of 0.0–0.5 wt% were considered. Experimental results showed that the stiffness and strength of the carbon aerogel toughened polymers steadily increased with the carbon aerogel content. The glass transition temperature of the unmodified epoxy polymer was 147 °C, and it was not appreciably affected by the addition of carbon aerogels. Blending the carbon aerogels with the epoxy polymer led to an appreciably improvement in the fracture performance of the resulting composites. For example, the fracture energy of the unmodified polymer was 125 J m−2, whereas that of an epoxy polymer reinforced with a carbon aerogel content of 0.3 wt% was 255 J m−2. The mechanisms responsible for the toughness enhancement were identified by studying the fracture surfaces using field emission gun scanning electron microscopy. Crack pinning, crack deflection, interfacial debonding, and plastic void growth were the main toughening mechanisms in the carbon aerogel toughened epoxy polymers.

Experimental investigations of aerogel-incorporated ultra-high performance concrete

Improvements to concrete will have a large impact in the construction and building sector. As the attention is drawn towards energy-efficient and zero emission buildings, the thermal properties of concrete will be important. Attempts are being made to decrease the thermal conductivity of concrete composites while retaining as much as possible of the mechanical strength. In this study experimental investigations of aerogel-incorporated mortar (AIM) with up to 80vol% aerogel are prepared utilizing a reduced ultra-high performance concrete (UHPC) recipe. It was found that at 50vol% aerogel content, the AIM sample possessed a compressive strength of 20MPa and a thermal conductivity of ≈0.55W/(mK). This strength decreased by almost a factor of 4–5.8MPa, while gaining only a 20% improvement in thermal conductivity when aerogel content increased to 70vol%. No preferred gain in properties was observed as compared to a normal mortar system. This can be attributed to the imbalance of the particle–matrix ratio in the mortar system, causing a decrease in adhesion of the binder-aggregates. The AIM samples have been characterized by thermal conductivity and mechanical strength measurements, alongside scanning electron microscope (SEM) analyses.