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The lightweight ablation materials that have been successfully applied in thermal protection systems (TPS) are the focus of attention owing to the urgent demand for aerospace vehicles to have efficient thermal insulation materials with lightweight, long-term antioxidant, and micro-ablation. However, improving the antioxidant ablation properties in a long-term aerobic atmosphere is still a significant challenge. Herein, a novel strategy to fabricate needle quartz fiber (NQF) reinforced SiO 2 aerogel interpenetrating polybenzoxazine (PBO) aerogel thermal protection composites (NQF/SiO 2 –PBOs) with a binary network structure is proposed. The as-prepared NQF/SiO 2 –PBOs perfectly inherited their porous nanostructure and captivating properties, including lightweight (0.53 g/cm3), high mechanical strengths, and low thermal conductivity of 0.048 W/(m·K) at 25 °C and 0.079 W/(m·K) at 1100 °C. Moreover, the NQF/SiO 2 –PBOs exhibited outstanding high-temperature thermal insulation and long-time antioxidant ablation with low linear and mass ablation rates. The cold surface temperature peaked at approximately 307.2 °C within 1800 s when the hot surface temperature exceeded 1100 °C. The ablation/thermal insulation mechanism was also discussed through the analysis of the microstructure, chemical structure, and crystal structure. This research provides a meaningful reference for the development and exploitation of new advanced lightweight, long-term antioxidant, and micro-ablative thermal protective materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • The facile preparation of PBz aerogel with excellent thermal insulation performance is realized. • The char yields of PBz aerogel reach 55.00 % at 600 °C. • The obtained PBz aerogel demonstrates a low thermal conductivity of 0.0313 W m−1 K−1 at 25 °C. • The obtained PBz aerogel exhibits super-hydrophobicity and outstanding mechanical properties. Polybenzoxazine (PBz) aerogels with outstanding mechanical properties and thermal insulation have attracted significant attention because of their classification as the most advanced and efficient thermal insulation material. However, the complex and environmentally unfriendly preparation technology has consistently hindered the performance improvement and broad practical applications of PBz aerogels. Herein, we report a facile preparation method of PBz aerogels through an aqueous solution system and ambient pressure drying (APD), thereby overcoming the limitations of the conventional methods. The resulting PBz aerogel exhibits lightweight (0.194 g cm−3), efficient thermal insulation, low thermal conductivity (0.0313 W m−1 K−1), self-extinguishing, super-hydrophobicity (contact angle of 148°), and remarkable mechanical properties. This study proposes a cutting-edge approach to fabricate PBz aerogels, which further amplifies their potential application in the field of thermal insulation. [ABSTRACT FROM AUTHOR]

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, CO 2 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. [Display omitted] • Polybenzoxazine (PBz) aerogels present a wide-ranging potential for applications as emerging high-performance materials. • Elaborate summaries of preparation routes for PBz aerogels. • The microscopic morphology of PBz aerogels can be modulated through colloid chemistry principles. • Comprehensive introduction of composite and hybrid materials based on PBz aerogels. • Challenges and potential development directions faced by PBz aerogels. [ABSTRACT FROM AUTHOR]

• A boric acid-regulated sol–gel transition strategy is used to achieve modulation of the morphology. • Ethanol is employed as a green solvent for the preparation of boron-doped polybenzoxazine (BPBz) aerogels. • The introduction of boric acid provides multifunctional properties to BPBz aerogels. • The BPBz aerogels exhibit intrinsic and alterable wettability that correlates with their morphologies. Polybenzoxazine aerogels have gained widespread attention in recent years, but the prevalent use of hazardous solvents in the preparation process has severely impeded their further development and promotion for practical applications. Herein, using ethanol as a solvent, a strategy of boric acid-induced microstructure regulation is proposed to construct boron-doped polybenzoxazine (BPBz) aerogels, which provides a feasible approach to overcome the above situation. The introduction of boric acid enhances the backbone strength by forming intermolecular bridged structures between PBz chains and allows the use of ambient pressure drying. The resulting BPBz aerogel demonstrates high stiffness (specific modulus up to 255.97 kN·m·kg−1), low bulk density (0.203 g·cm−3), and low thermal conductivity (0.043 W·m−1·K−1), exhibiting excellent fire resistance when exposed to a 1200 °C flame (the self-extinguishing interval less than 1 s). More interestingly, the aerogel demonstrates intrinsic and tunable wettability that correlates with the morphology. Combining the environmentally friendly preparation strategy and these advantages, BPBz aerogels hold promise for thermal management and fire protection applications in energy-saving construction and other harsh conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lightweight polybenzoxazine (PBz) aerogels were fabricated by hexamethylene diisocyanate (HDI) modification. • The introduction of HDI formed a covalent-crosslinked structure with the chemical structure of the PBz aerogel. • The HDI-modified PBz aerogel demonstrates a self-extinguishing time of less than 1 s after removal from a 1200 °C flame. The rapid advancement of modern industries has imposed demands on thermal insulators that possess not only low thermal conductivities but also multifunctional properties. Polybenzoxazine (PBz) aerogels with several advantages have garnered considerable research interest in recent years. Nevertheless, PBz aerogels acquired from ambient pressure drying still confront the challenge of exhibiting relatively high densities and thermal conductivities. In this study, to enrich the category and propose practical ideas for overcoming the above plight, hexamethylene diisocyanate (HDI) was selected as an additive to prepare lightweight and efficient thermal-insulating PBz aerogels through chemical modification. Compared with the pristine specimens (0.268 g·cm−3, 0.0387 W·m−1·K−1), the HDI-modified PBz aerogels exhibited lower densities (0.237–0.256 g·cm−3) and thermal conductivities (0.0354–0.0370 W·m−1·K−1). Moreover, the introduction of HDI has been demonstrated to not impact their superior intrinsic flame retardance, despite an observed reduction in the residual char yields in the HDI-modified groups. Given these excellent properties, PBz-HDI aerogels are expected to be promising candidates for thermal insulation and fire resistance applications. [ABSTRACT FROM AUTHOR]