Flammability of Polymer/Clay Aerogel Composites: An Overview

Ionic-physical-chemical triple cross-linked all-biomass-based aerogel for thermal insulation applications

Aerogels, as a unique porous material, are expected to be used as insulation materials to solve the global environmental and energy crisis. Using chitosan, citric acid, pectin and phytic acid as raw materials, an all-biomass-based aerogel with high modulus was prepared by the triple strategy of ionic, physical and chemical cross-linking through directional freezing technique. Based on this three-dimensional network, the aerogel exhibited excellent compressive modulus (24.89 ± 1.76 MPa) over a wide temperature range and thermal insulation properties. In the presence of chitosan, citric acid and phytic acid, the aerogel obtained excellent fire safety (LOI value up to 31.2%) and antibacterial properties (antibacterial activity against Staphylococcus aureus and Escherichia coli reached 81.98% and 67.43%). In addition, the modified aerogel exhibited excellent hydrophobicity (hydrophobic angle of 146°) and oil-water separation properties. More importantly, the aerogel exhibited a biodegradation rate of up to 40.31% for 35 days due to its all-biomass nature. This work provides a green and sustainable strategy for the production of highly environmentally friendly thermal insulation materials with high strength, flame retardant, antibacterial and hydrophobic properties.

Renewable biomass-based aerogels: from structural design to functional regulation

Global population growth and industrialization have exacerbated the nonrenewable energy crises and environmental issues, thereby stimulating an enormous demand for producing environmentally friendly materials. Typically, biomass-based aerogels (BAs), which are mainly composed of biomass materials, show great application prospects in various fields because of their exceptional properties such as biocompatibility, degradability, and renewability. To improve the performance of BAs to meet the usage requirements of different scenarios, a large number of innovative works in the past few decades have emphasized the importance of micro-structural design in regulating macroscopic functions. Inspired by the ubiquitous random or regularly arranged structures of materials in nature ranging from micro to meso and macro scales, constructing different microstructures often corresponds to completely different functions even with similar biomolecular compositions. This review focuses on the preparation process, design concepts, regulation methods, and the synergistic combination of chemical compositions and microstructures of BAs with different porous structures from the perspective of gel skeleton and pore structure. It not only comprehensively introduces the effect of various microstructures on the physical properties of BAs, but also analyzes their potential applications in the corresponding fields of thermal management, water treatment, atmospheric water harvesting, CO2 absorption, energy storage and conversion, electromagnetic interference (EMI) shielding, biological applications, etc. Finally, we provide our perspectives regarding the challenges and future opportunities of BAs. Overall, our goal is to provide researchers with a thorough understanding of the relationship between the microstructures and properties of BAs, supported by a comprehensive analysis of the available data.

Research progress on polybenzoxazine aerogels: Preparation, properties, composites and hybrids fabrication, applications

The unremitting pursuit of high-performance and multifunctional materials has consistently propelled modern industries forward, stimulating research and motivating progress in related fields. In such materials, polybenzoxazine (PBz) aerogel, which combines the virtues of PBz and aerogel, has attracted salient attention recently, emerging as a novel research focus in the realm of advanced materials. In this review, the preparation scheme, microscopic morphology, and fundamental characteristics of PBz aerogels are comprehensively summarized and discussed in anticipation of providing a clear understanding of the correlation between preparation process, structure, and properties. The effective strategies for enhancing the performance of PBz aerogels including composite fabrication and hybridization are highlighted. Moreover, the applications of PBz-based aerogels in various domains such as adsorption (including wastewater treatment, CO2 capture, and microwave adsorption), thermal insulation, energy storage as well as sensors are covered in detail. Furthermore, several obstacles and potential directions for subsequent research are delineated with a view to surmounting the prevailing constraints and achieving a realization of the shift from experimental exploration to practical applications.

Nanoclay-reinforced alginate aerogels: preparation and properties

Flame-retardant materials that are mechanically robust, low cost and non-toxic from green and renewable resources are highly demanded in many fields. In this work, aerogels of alginate extracted from seaweeds were fabricated and reinforced with nanoclay. The nanoclay particles increase the molecular ordering (crystallinity) of the aerogels through physical interactions with alginate molecules. They also served as cross-linkers and flame-retardant additives to improve the mechanical strength, elasticity, thermal stability and flame-retarding properties of the aerogels. Under exposure to a butane flame (750 °C), the aerogels maintained their structural integrity and did not produce drips. An optimal loading of nanoclay which led to the best flame retardancy (non-flammable) of the aerogel was determined. The results of this work demonstrate that alginate-nanoclay composite aerogels can be promisingly used as flame-retardant thermal insulation materials.

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.

Development of a New Clay-Based Aerogel Composite from Ball Clay from Piauí, Brazil and Polysaccharides

The incorporation of polymeric components into aerogels based on clay produces a significant improvement in the physical and thermal properties of the aerogels. In this study, clay-based aerogels were produced from a ball clay by incorporation of angico gum and sodium alginate using a simple, ecologically acceptable mixing method and freeze-drying. The compression test showed a low density of spongy material. In addition, both the compressive strength and the Young's modulus of elasticity of the aerogels showed a progression associated to the decrease in pH. The microstructural characteristics of the aerogels were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The chemical structure was studied by infrared spectroscopy with Fourier transform (FTIR). The TGA curves from a non-oxidizing atmosphere indicated that the clay had a mass loss of 9% above 500 °C and that due to the presence of polysaccharides, the aerogels presented a decomposition of 20% at temperatures above 260 °C. The DSC curves of the aerogels demonstrated a displacement in higher temperatures. In conclusion, the results showed that aerogels of ball clay with the incorporation of polysaccharides, which are still minimally studied, have potential application as thermal insulation considering the mechanical and thermal results obtained.

Konjac Glucomannan Aerogels Modified by Hydrophilic Isocyanate and Expandable Graphite with Excellent Hydrolysis Resistance, Mechanical Strength, and Flame Retardancy

At present, biomass foamlike materials are a hot research topic, but they need to be improved urgently due to their defects such as large size shrinkage rate, poor mechanical strength, and easy hydrolysis. In this study, the novel konjac glucomannan (KGM) composite aerogels modified with hydrophilic isocyanate and expandable graphite were prepared by a facile vacuum freeze-drying method. Compared with the unmodified KGM aerogel, the volume shrinkage of the KGM composite aerogel (KPU-EG) decreased from 36.36 ± 2.47% to 8.64 ± 1.46%. Additionally, the compressive strength increased by 450%, and the secondary repeated compressive strength increased by 1476%. After soaking in water for 28 days, mass retention after hydrolysis of the KPU-EG aerogel increased from 51.26 ± 2.33% to more than 85%. The UL-94 vertical combustion test showed that the KPU-EG aerogel can achieve a V-0 rating, and the limiting oxygen index (LOI) value of the modified aerogel can reach up to 67.3 ± 1.5%. To sum up, the cross-linking modification of hydrophilic isocyanate can significantly improve the mechanical properties, flame retardancy, and hydrolysis resistance of KGM aerogels. We believe that this work can provide excellent hydrolytic resistance and mechanical properties and has broad application prospects in practical packaging, heat insulation, sewage treatment, and other aspects.

Highly Efficient Flame-Retardant and Enhanced PVA-Based Composite Aerogels through Interpenetrating Cross-Linking Networks

Poly(vinyl alcohol) (P)/alginate (A)/MMT (M) (PAM) composite aerogels was modified through interpenetrating cross-linking of methyltriethoxysilane (Ms) or γ-aminopropyltriethoxysilane (K) and calcium ion (Ca²⁺) as a cross-linking agent, respectively. The compressive moduli of the cross-linked PAM/MsCa and PAM/KCa aerogels greatly increased to 17.4 and 22.1 MPa, approximately 10.5- and 8.2-fold of that of PAM aerogel, respectively. The limited oxygen index (LOI) values for PAM/MsCa and PAM/KCa composite aerogels increased from 27.0% of PAM aerogel to 40.5% and 56.8%. Compared with non-cross-linked PAM aerogel, the peak heat release rate (PHRR) of PAM/MsCa and PAM/KCa composite aerogels dramatically decreased by 34% and 74%, respectively, whereas the PAM/KCa aerogel presented better flame retardancy and lower smoke toxicity than the PAM/MsCa aerogel because of the release of more inert gases and the barrier action of more compact char layer during the combustion. The highly efficient flame-retardant PAM-based composite aerogels with excellent mechanical properties are promising as a sustainable alternative to traditional petroleum-based foams.

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-AP_x (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-AP_x aerogel composites. Based on the combination of thermogravimetric analysis and combustion behavior, the PVA-MMT-AP_x 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.

Thermal and flame-retardant properties of multilayered composites prepared through novel multilayering approach

Thermal and flame-retardant properties of traditional composites have limitations that are not satisfied for the various applications. Multilayered materials have great potential to improve material properties. The present paper focused on designing new multilayering approach to fabricate flame retardant multilayered materials with a very basic instrument and several simple steps. Montmorillonite nanoparticles filled maleic anhydride grafted polypropylene composites were prepared by the melt-blending method, and the multilayered composites with polypropylene alternating multilayers were fabricated by the quadruple-layering approach. The multilayer structure was characterized by the scanning electron microscopy/energy dispersive spectrometer. The influence of layer structure on the thermal stability, thermal conductivity and flame-retardant properties was investigated by the comparison with the conventional composites. Multilayered composites showed enhanced flame-retardant properties with lower peak heat release rate and better char formation compared to conventional composites with the same mass fraction of montmorillonite. Multilayered composites had higher mass fraction of montmorillonite in filled layers and no fillers in other layers, which caused the unequal distribution of montmorillonite, resulting in changes of thermal and flame-retardant properties of the materials especially in the perpendicular direction to the film surface. This study demonstrates a unique multilayering approach that has potential to be used in variety applications such as food and medical packaging.

Shaping 90 wt% NanoMOFs into Robust Multifunctional Aerogels Using Tailored Bio-Based Nanofibrils

Metal-organic frameworks (MOFs) are hybrid porous crystalline networks with tunable chemical and structural properties. However, their excellent potential is limited in practical applications by their hard-to-shape powder form, making it challenging to assemble MOFs into macroscopic composites with mechanical integrity. While a binder matrix enables hybrid materials, such materials have a limited MOF content and thus limited functionality. To overcome this challenge, nanoMOFs are combined with tailored same-charge high-aspect-ratio cellulose nanofibrils (CNFs) to manufacture robust, wet-stable, and multifunctional MOF-based aerogels with 90 wt% nanoMOF loading. The porous aerogel architectures show excellent potential for practical applications such as efficient water purification, CO₂ and CH₄ gas adsorption and separation, and fire-safe insulation. Moreover, a one-step carbonization process enables these aerogels as effective structural energy-storage electrodes. This work exhibits the unique ability of high-aspect-ratio CNFs to bind large amounts of nanoMOFs in structured materials with outstanding mechanical integrity-a quality that is preserved even after carbonization. The demonstrated process is simple and fully discloses the intrinsic potential of the nanoMOFs, resulting in synergetic properties not found in the components alone, thus paving the way for MOFs in macroscopic multifunctional composites.

Microstructural transition of poly(vinyl alcohol)-based aerogels in the presence of interpolymer complexes

Interpolymer interactions play a vital role of determining the microstructure and properties of polymer aerogels.

In situ nanoarchitectonics of magnesium hydroxide particles for property regulation of carboxymethyl cellulose/poly(vinyl alcohol) aerogels

Carboxymethyl cellulose (CMC)-based aerogels with low density, low thermal conductivity, and biodegradability are promising candidates for environmentally friendly heat-insulating materials. However, the application of CMC-based aerogels as insulation materials in building exterior walls is limited by the high water sensitivity, poor mechanical properties and high flammability of these aerogels. In this work, a simple hydration method was used to generate magnesium hydroxide (MH) directly from CMC/polyvinyl alcohol (PVA) mixed sol with active MgO obtained by calcined magnesite as the raw material. A series of composite aerogels with different MH contents were prepared through the freeze-drying method. Scanning electron microscopy showed that nanoflower-like MH was successfully synthesised in situ in the 3D porous polymer aerogel matrix. Compared with the mechanical properties and water resistance of the original CMC/PVA composite aerogels, those of the composite aerogels were significantly improved. In addition, the flame retardancy of the CMC/PVA composite aerogels was greatly enhanced by the introduction of MH into the polymer matrix, and the limiting oxygen index reached 35.5% when the MH loading was 60%.

Flame retardant efficiency of magnesium hydroxide in cellulose aerogels improved by in situ formation.

Disorder-Order Transition-Improving the Moisture Sensitivity of Waterborne Nanocomposite Barriers

Systematic studies on the influence of crystalline vs disordered nanocomposite structures on barrier properties and water vapor sensitivity are scarce as it is difficult to switch between the two morphologies without changing other critical parameters. By combining water-soluble poly(vinyl alcohol) (PVOH) and ultrahigh aspect ratio synthetic sodium fluorohectorite (Hec) as filler, we were able to fabricate nanocomposites from a single nematic aqueous suspension by slot die coating that, depending on the drying temperature, forms different desired morphologies. Increasing the drying temperature from 20 to 50 °C for the same formulation triggers phase segregation and disordered nanocomposites are obtained, while at room temperature, one-dimensional (1D) crystalline, intercalated hybrid Bragg Stacks form. The onset of swelling of the crystalline morphology is pushed to significantly higher relative humidity (RH). This disorder-order transition renders PVOH/Hec a promising barrier material at RH of up to 65%, which is relevant for food packaging. The oxygen permeability (OP) of the 1D crystalline PVOH/Hec is an order of magnitude lower compared to the OP of the disordered nanocomposite at this elevated RH (OP = 0.007 cm³ μm m^-2 day^-1 bar^-1 cf. OP = 0.047 cm³ μm m^-2 day^-1 bar^-1 at 23 °C and 65% RH).

Reduction of PVA Aerogel Flammability by Incorporation of an Alkaline Catalyst

Sodium hydroxide was used as a base catalyst to reduce the flammability of poly(vinyl alcohol) (PVA) aerogels. The base-modified aerogels exhibited significantly enhanced compressive moduli, likely resulting in decreased gallery spacing and increased numbers of “struts” in their structures. The onset of decomposition temperature decreased for the PVA aerogels in the presence of the base, which appears to hinder the polymer pyrolysis process, leading instead to the facile formation of dense char. Cone calorimetry testing showed a dramatic decrease in heat release when the base was added. The results indicate that an unexpected base-catalyzed dehydration occurs at fire temperatures, which is the opposite of the chemistry normally observed under typical synthesis conditions.

Low-Density Silk Nanofibrous Aerogels: Fabrication and Applications in Air Filtration and Oil/Water Purification

A method was developed to fabricate light, water-insoluble silk fibroin nanofibrous aerogels (SNFAs) through solvent welding of lyophilized silk nanofibrous 3D networks at the junction points while converting silk structures from random-coils to β-sheets (water insoluble). Aromatic alcohols, especially phenethyl alcohol (PEA), supported robust solvent welding and the structural conversion of silk. PEA vapor treatment was a better approach than solvent infusion to retain volume, density, and mechanical strength of the SNFAs. The mechanical properties of highly orientated SNFAs were superior to randomly distributed fibers. The SNFAs had a low density (3.5 mg/cm³), high hydrophobicity (140.9°), and a porous surface morphology on the individual nanofibers, resulting in high efficiency and selectivity for absorbing particulate matter and oils. Compared with commonly used inorganic aerogels, the SNFAs developed in this study are biocompatible, easily functionalized, environmentally friendly, and low-cost and therefore have potential for air and water purification, biosensors, drug delivery, and tissue engineering.

Biomimetic Amyloid-like Protein/Laponite Nanocomposite Thin Film through Regulating Protein Conformation

The use of natural protein-based thin films has been severely limited because of their relatively low stiffness and strength compared to synthetic polymers. Although the mechanical properties of the protein-based thin films could be enhanced through blending with nanofillers, the fabrication of these materials with nanoscale-to-macroscale hierarchical architecture and robust interfacial adhesion via a facile and green method remains a challenge. Here, we prepared robust protein-based organic/inorganic nanocomposite films with a nacre-like microstructure through directly regulating protein conformation in a simple and biocompatible all-aqueous system. These films contain a high concentration of laponite (Lap) and amyloid-like phase-transited bovine serum albumin (PTB) aggregates rich in β-sheets, which could organize Lap nanoplatelets into an intercalated and multistacked structure. In addition, the PTB aggregates present strong mechanical strength, good stability, and especially superior bioadhesion to afford strong organic/inorganic interface bonding. The resultant PTB/Lap films exhibit high Young's modulus and strength and good chemical stability (in both aqueous solution and organic solvent) and flame retardation, while they are also very transparent (maintaining more than 90% transmittance). Moreover, the film could adhere onto various substrates with robust biomimetic interfacial adhesion, and the resultant coating on glass could function as a smart window to cool down the indoor temperature. Because of their excellent performance and high versatility, the amyloid-like protein/clay nanocomposite films are expected to find broad practical applications.

Large, Rapid Swelling of High-cis Polydicyclopentadiene Aerogels Suitable for Solvent-Responsive Actuators

High-cis polydicyclopentadiene (PDCPD) aerogels were synthesized using ring opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD) with a relatively air-stable ditungsten catalytic system, Na[W₂(-Cl)₃Cl₄(THF)₂]·(THF)₃ (W₂; (W ³ W)⁶⁺, a΄²e΄⁴), and norbornadiene (NBD)as a co-initiator. These aerogels are compared in terms of chemical structure and material properties with literature PDCPD aerogels obtained using well-established Ru-based alkylidenes as catalysts. The use of NBD as a co-initiator enhances the degree of crosslinking versus the more frequently used phenylacetylene (PA), yielding materials with a controlled molecular structure that would persist solvent swelling. Indeed, those PDCPD aerogels absorb selected organic solvents (e.g., chloroform, tetrahydrofuran) and swell rapidly, in some cases up to 4 times their original volume within 10 min, thus showing their potential for applications in chemical sensors and solvent-responsive actuators. The advantage of aerogels versus xerogels or dense polymers for these applications is their open porosity, which provides rapid access of the solvent to their interior, thus decreasing the diffusion distance inside the polymer itself, which in turn accelerates the response to the solvents of interest.

Ultralight and Hydrophobic Palygorskite-based Aerogels with Prominent Thermal Insulation and Flame Retardancy

Clay-based aerogel is a promising material in the field of thermal insulation and flame retardant, but obtaining clay-based aerogel with high fire resistance, low thermal conductivity, hydrophobicity, and mechanical robustness remains a challenge. In this work, palygorskite-based aerogel was successfully fabricated via combining with a very small proportion of alginate to form a distinctive hierarchically meso-microporous structure. By employing ethanol solution (EA) replacement method and freeze-drying process, the resultant aerogel exhibited ultralow density (0.035-0.052 g/cm³), practical mechanical strengths (0.7-2.1 MPa), and low thermal conductivity of 0.0332-0.165 W/mK (25-1000 °C). The hydrophobicity of aerogel was achieved by simple chemical vapor deposition of methyltrimethoxysilane (MTMS). The Pal-based aerogel showed good performance in both fire resistance with high limiting oxygen index up to 90%, and heat resistance with tolerance of flame up to 1000 °C for 10 min. This renewable Pal-based aerogel with a 3D framework is a promising material to be applied in fields of construction and aerospace for thermal insulation and high fire resistance.

Gradient-Structured Nonflammable Flexible Polymer Membranes

Herein, we report the formation and properties of a rare example of high-performance composite membranes from polybisbenzimidazobenzophenanthroline-dione (BBB) that do not sustain a flame or burn with smoke nor show melt dripping. In addition, this material possesses a low density and very high thermal stability (char yield as high as 80-94%), strength, and flexibility. Such membranes are highly desirable for battery separators, protective clothing, construction, and automobiles. Because BBB is an insoluble and infusible polymer, the composite membranes were made using a bottom-up vacuum-assisted self-assembly method with an aqueous dispersion of short BBB fibers and Hec. The use of water as the solvent, upscalability, and excellent flame retardancy in combination with low density, flexibility, and low thermal conductivity of the composite membranes make the preparation method and membranes highly promising for future use in real applications.

Poly(Urethane-Acrylate) Aerogels via Radical Polymerization of Dendritic Urethane-Acrylate Monomers

The purpose of this work was to investigate the effect of multifunctionality on material properties of synthetic polymer aerogels. For this purpose, we present the synthesis and characterization of monolithic dendritic-type urethane-acrylate monomers based on an aliphatic/flexible (Desmodur N3300), or an aromatic/rigid (Desmodur RE) triisocyanate core. The terminal acrylate groups (three at the tip of each of the three branches, nine in total) were polymerized with 2,2'-azobis(isobutyronitrile) (AIBN) via free radical chemistry. The resulting wet-gels were dried with supercritical fluid (SCF) CO₂. Aerogels were characterized with ATR-FTIR and solid-state 13C NMR. The porous network was probed with N₂-sorption and scanning electron microscopy (SEM). The thermal stability of aerogels was studied with thermogravimetric analysis (TGA). Most aerogels were macroporous materials (porosity > 80%), with high thermal stability (up to 300 °C). Aerogels were softer at low monomer concentrations and more rigid at higher concentrations. The material properties were compared with those of analogous aerogels bearing only one acrylate moiety at the tip of each branch and the same cores, and with those of analogous aerogels bearing norbornene instead of acrylate moieties. The nine-terminal acrylate-based monomers of this study caused rapid decrease of the solubility of the growing polymer and made possible aerogels with much smaller particles and much higher surface areas. For the first time, aliphatic/flexible triisocyanate-based materials could be made with similar properties in terms of particle size and surface areas to their aromatic/rigid analogues. Finally, it was found that with monomers with a high number of crosslinkable groups, material properties are determined by multifunctionality and thus aerogels based on 9-acrylate- and 9-norbornene-terminated monomers were similar. Materials with aromatic cores are carbonizable with satisfactory yields (20⁻30% w/w) to mostly microporous materials (BET surface areas: 640⁻740 m² g-1; micropore surface areas: 360⁻430 m² g-1).

Millimeter-Size Spherical Polyurea Aerogel Beads with Narrow Size Distribution

We report the room temperature synthesis of spherical millimeter-size polyurea (PUA) aerogel beads. Wet-gels of said beads were obtained by dripping a propylene carbonate solution of an aliphatic triisocyanate based on isocyanurate nodes into a mixture of ethylenediamine and heavy mineral oil. Drying the resulting wet spherical gels with supercritical fluid (SCF) CO₂ afforded spherical aerogel beads with a mean diameter of 2.7 mm, and a narrow size distribution (full width at half maximum: 0.4 mm). Spherical PUA aerogel beads had low density (0.166 ± 0.001 g cm⁻3), high porosity (87% v/v) and high surface area (197 m² g⁻1). IR, ¹H magic angle spinning (MAS) and 13C cross-polarization magic angle spinning (CPMAS) NMR showed the characteristic peaks of urea and the isocyanurate ring. Scanning electron microscopy (SEM) showed the presence of a thin, yet porous skin on the surface of the beads with a different (denser) morphology than their interior. The synthetic method shown here is simple, cost-efficient and suitable for large-scale production of PUA aerogel beads.