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Bio-based aerogels, which are poised as compelling thermal insulators, demand intricate synthesis procedures and have limited durability under harsh conditions. The integration of smart stimuli–response transitions in biomass aerogels holds promise as a solution, yet remains a challenge. Here, we introduce a pioneering strategy that employs reversible-gel-assisted ambient-pressure drying without organic solvents to craft multifunctional bio-based aerogels. By exploiting the thermally reversible gelling propensity of select biomasses, we anchor emulsified bubbles within cross-linked hydrogels, circumventing surface tension issues during mild drying. The resultant aerogels feature a robust porous matrix that is imbued with stable bubbles, yielding low thermal conductivity, high flame retardancy and robust resistance to diverse rigors. This innovative approach facilitates a paradigm shift in intelligent fire protection in which aerogels transition from robust to flexible in response to water stimuli, effectively shielding against thermal hazards and external forces. This work opens up a facile, eco-friendly and mild way to fabricate advanced biomass aerogels with stimuli-responsive transformation. [ABSTRACT FROM AUTHOR]

Abstract Mechanically-strong sodium alginate/clay aerogel were fabricated by addition of p-toluenesulfonic acid using a freeze-drying method. The adjusting of pH from 8 (the control) to 6, on the one hand lead to the crosslinking of alginate, on the other hand thickened the clay sol. The compressive modulus of A5C5 aerogel significantly increased from 6.0 ± 0.4 MPa (pH = 8) to 17 ± 3 MPa (pH = 6). The morphological structure characterization showed that the microstructure of aerogels changed from layered to network with decreasing pH value, with cell size ranging from 4 to 8 μm. The rheological behavior showed that the addition of p-toluenesulfonic acid would significantly improve the viscosity of the precursors at low frequency. The combustion tests indicated that all the alginate/clay aerogels possess excellent flame retardancy. The addition of p-toluenesulfonic acid further slightly increased the thermal stability and fire safety of the material. This facile preparation procedure of strengthened polymer/clay aerogel via adjusting pH is promising and can be spread. [ABSTRACT FROM AUTHOR]

Highlights • Self-cross-linked aerogel based on pectin and melamine-formaldehyde resin was fabricated. • MF-pectin aerogels have significantly increased compressive moduli. • MF-pectin aerogels possess excellent water resistance and low flammability. Abstract Self-cross-linked aerogel based on pectin and melamine-formaldehyde resin (MF) was fabricated via freeze-drying method using water as solvent, where pectin is structural material meanwhile acting as acid to catalyse the cross-linking of MF. The cross-linking reaction easily occurs without additional additives, which can be significantly accelerated at elevated temperatures, with a critical value of about 55 °C. The obtained aerogel shows network microstructures as observed with SEM. With increasing pectin content, the aerogel shows significantly increased compressive modulus. The compressive modulus of M10Pe5 arrives 23.2 MPa, the specific modulus of which arrives 188 MPa cm3/g, while pure MF aerogel are too fragile to keep intact after freeze-dried. The resulting aerogel has good thermal stability, excellent water resistance (can be second dried with limited strength loss) and low flammability. This partially bio-based novel aerogel with impressive properties is promising in many applications. [ABSTRACT FROM AUTHOR]

Biomass aerogels possessing both resilience and flame retardance exhibit great potential as alternatives to fossil-based thermal insulators. Nevertheless, the functional applications of elastic biomass aerogels are impeded by their poor resilience persistence, especially at low temperatures. Herein, a synergetic strategy was proposed for designing biomass aerogels with exceptional elasticity across a broad temperature range (from 150 °C to −78 °C), by strategically manipulating their microstructure and implementing a chemically cross-linked network. The resultant aerogels suffered from slight plastic deformation of only 6.1 % even after 1000 loading-unloading cycles at a strain of 60 %, manifesting super-elastic performance. Additionally, the structure and resilience of aerogel can be well maintained even under frigid temperatures (−78 °C). Because firmly cross-linked networks and loosely packed microstructures with elongated cell walls were constructed to minimize plastic deformation and bending stress, thereby suppressing structural destruction. Furthermore, the resulting biomass aerogel exhibited a remarkable combination of advantageous properties including lightweight, flame retardance (limiting oxygen index of 29 %), thermal insulation (32.8 mW m−1 K−1) and infrared stealth. This research offers new insights into the design of elastic biomass aerogels with exceptional overall performance. By strategically manipulating the microstructure and implementing a chemically cross-linked network, a biomass aerogel was fabricated with flame retardance, thermal insulation, and exceptional elasticity across a wide temperature range. [Display omitted] • Bomass aerogel was prepared with super-elasticity by manipulating microstructure and chemical cross-linked networks. • Cross-linked networks and loose microstructures with elongated walls minimize deformation and bending stress, suppressing destruction. • The resilient performance of aerogels can be maintained from 150 °C to −78 °C. • This aerogel exhibits lightweight, flame retardance, thermal insulation and infrared stealth. [ABSTRACT FROM AUTHOR]

Atmospheric drying method for fabricating aerogels is considered the most promising way for casting aerogels on a large scale. However, the organic solvent exchange, remaining environmental pollution risk, is a crucial step in mitigating the impact of surface tension during the atmospheric drying process, especially for wet gel formed through the alkoxy-derived sol-gel process, such as melamine-formaldehyde resin (MF) aerogel. Herein, a tough polymer-assisted in situ polymerization was proposed to fabricate MF resin aerogel with a combination of mechanical toughness and strength, enabling it to withstand the capillary force during water evaporation. The monolithic MF resin aerogel through the sol-gel method can be directly prepared without additional network strengthening or organic solvent exchange. The resulting MF resin aerogel exhibits a homogeneous as well as hierarchical structure with macropores and mesopores (~6 μm and ~5 nm), high compressive modulus of 31.8 MPa, self-extinguishing property, and high-temperature thermal insulation with 97 % heat decrease for butane flame combustion. This work presents a straightforward and environmentally friendly method for fabricating MF resin aerogels with nanostructures and excellent performance in open conditions, exhibiting various applications. • A tough biomass-assisted in situ polymerization is proposed for the fabrication of melamine-formaldehyde (MF) resin aerogel via the atmospheric drying method. • Benefiting from the robust cross-linking networks and homogeneous porous structures, the MF resin aerogel displayed a modulus of 31.8 MPa. • The MF resin aerogel exhibits superior flame retardance with a limiting oxygen index value of 35.5% and high temperature insulation. [ABSTRACT FROM AUTHOR]

Aerogel composites based on melamine-formaldehyde (MF) and alginate (A) was fabricated with ice-templated method. The preparation process involves two cross-linking processes, in aerogel precursor at room temperature and in dried aerogel at 80 °C (100% humidity), respectively. Cross-linking was demonstrated to be very efficient for improving the mechanical property and water resistance of MF-A aerogels. The obtained aerogels have compressive moduli ranging from 1.2 MPa to 24.1 MPa. All the cross-linked aerogels display good dimensional stability when soaked in water. The morphological study of MF-A aerogels show a layered or network microstructure, with a homogeneous distribution of MF spheres. Due to low density and porous structure, MF-A aerogels have low thermal conductivity from 0.035 to 0.047 W/m K. MF-A aerogels have good thermal stability and extremely low flammability, with LOI value up to 41%. This novel aerogel from partially bio-based raw material would have promising application prospects. Image 10735 • Fully organic aerogel based on melamine-formaldehyde and alginate was fabricated. • The resulting flame retardant aerogels possess low thermal conductivity. • The obtained aerogels are insoluble in water even fabricated from water solution. [ABSTRACT FROM AUTHOR]