Water-Induced Self-Assembly and In Situ Mineralization within Plant Phenolic Glycol-Gel toward Ultrastrong and Multifunctional Thermal Insulating Aerogels

Abstract

Biopolymer/silica nanocomposite aerogels are highly attractive as thermally insulating materials for prevailing energy-saving engineering but are usually plagued by their lack of mechanical strength and environmental stability. Lignin is an appealing plant phenolic biopolymer due to its natural abundance, high stiffness, water repellency, and thermostability. However, integrating lignin and silica into high-performance 3D hybrid aerogels remains a substantial challenge due to the unstable co-sol process. In diatoms, the silicic acid stabilization prior to the condensation reaction is enhanced by the intervention of biomolecules in noncovalent interactions. Inspired by this mechanism, we herein rationally design an ultrastrong silica-mineralized lignin nanocomposite aerogel (LigSi) with an adjustable multilevel micro/nanostructure and arbitrary machinability through an unusual water-induced self-assembly and in situ mineralization based on ethylene glycol-stabilized lignin/siloxane colloid. The optimized LigSi exhibits an ultrahigh stiffness (a specific modulus of ∼376.3 kN m kg −1 ) and can support over 5000 times its own weight without obvious deformation. Moreover, the aerogel demonstrates a combination of outstanding properties, including superior and humiditytolerant thermal insulation (maintained at ∼0.04 W m −1 K −1 under a relative humidity of 33−94%), excellent fire resistance withstanding an ∼1200 °C flame without disintegration, low near-infrared absorption (∼9%), and intrinsic self-cleaning/ superhydrophobic performance (158°WCA). These advanced properties make it an ideal thermally insulating material for diversified applications in harsh environments. As a proof of concept, a dual-mode LigSi thermal device was designed to demonstrate the application prospect of combining passive heat-trapping and active heating in the building.

Composition Regulation of Free Delignification of Wood Powder toward High Performance, Recyclable Composites

“…Solar radiation reaching the earth’s surface constitutes ultraviolet (UV) radiation (200–400 nm; 5%), visible light (400–780 nm; 46%), and infrared radiation (>780 nm; 49%) . It has been proven that the development of thermal insulating materials with high near-infrared (NIR) reflectance can minimize the thermal radiation from sunlight . Furthermore, it is especially expected that the structural material has favorable near-infrared reflectance …”

“…Although the average solar reflectance of WBC-50 has decreased, it still remained at ∼57 and ∼76% in VIS and NIR, respectively, which clearly showed an effective reflection of thermal energy from the radiative heat source. The high solar reflectance of WBCs is mainly attributed to its own layered structure and the strong intermolecular hydrogen bonds between wood powder and BC …”

“…Inflammability is a weakness of natural wood; thus, inorganic substances are always used to improve fire retardancy. 48 There is a high content of inorganic components in wood powder, and consequently, it is expected to play an important role in reducing the inflammability of WBCs (Figure S1, Supporting Information). The flame retardant behavior of WBCs under a forced fire scenario was further evaluated by cone calorimetry.…”

“…55 It has been proven that the development of thermal insulating materials with high near-infrared (NIR) reflectance can minimize the thermal radiation from sunlight. 48 Furthermore, it is especially expected that the structural material has favorable near-infrared reflectance. 56 A UV−vis−NIR test of WBCs with a 100 μm thickness was carried out to evaluate the reflectance of the solar irradiation spectrum.…”

“…The high solar reflectance of WBCs is mainly attributed to its own layered structure and the strong intermolecular hydrogen bonds between wood powder and BC. 48 We further characterized the spectroscopic performance of WBC-50 in the infrared region (Figure 6c). It exhibited a high emissivity ∼96% between 8 and 13 μm, which was comparable to those of other excellent radiative cooling materials.…”