基于多重氢键结构的纤维素纳米纤维/聚苯并恶嗪-聚乙烯醇双网气凝胶的制备与表征

A cellulose nanofiber/polybenzoxazine-polyvinyl alcohol(CNFs/PBZ-PVA)dual-network hybrid aerogel was fabricated for the first time by a"one-pot method"exploiting the physically cross-linked polyhydrogen bond structure.By integrating the rigidity of the CNFs-PVA network with the elasticity of the PBZ-PVA network,a dual-network aerogel structure with a balanced mechanical property and resilience was achieved.The experimental results demonstrate that:(1)Concerning the microstructure,it is revealed that the pore structure of CNFS-PVA(fiber stacking)and PBZ-PVA(uneven)is the main cause for their inferior mechanical properties,while CNFs/PBZ-PVA possesses a regular cellular network structure,uniform pore distribution(10～40 μm),and a porosity exceeding 97%.The density is 0.07g/cm3.Chemical analysis indicates that CNFs-PVA and PBZ-PVA networks form dense and uniform porous aerogels with multiple hydrogen bonds by introducing long-chain PBZ molecules and using polyvinyl alcohol as the intermediate carrier for physical crosslinking.(2)Regarding mechanical properties,CNFs/PBZ-PVA aerogels exhibit excellent resilience,recover rapidly after 60%compression deformation,and demonstrate fatigue resistance(the recovery rate can remain above 95%after 30 compression cycles).Additionally,after being treated with liquid nitrogen(-196℃),its resilience remains unaltered,overcoming the drawbacks of traditional nanocellulose-based aerogel materials such as poor resilience and brittleness.Intriguingly,under extremely acidic or alkaline conditions,the hybrid aerogels show excellent chemical stability,expanding their potential applications under extreme circumstances.(3)In terms of thermal stability,the introduction of the PBZ molecular chain leads to a decrease in the thermal decomposition rate of CNFs/PBZ-PVA at a higher temperature stage(200-500℃)(the thermal decomposition temperature increases by approximately 60℃),and one of the reasons for the faster thermal decomposition rate of the CNFS-PVA aerogel is the weak force of a single hydrogen bond.The structure of multiple hydrogen bonds enables CNFs/PBZ-PVA to have significant thermal insulation properties on the heating plate,and the surface temperature of the CNFS-PVA aerogel is reduced by 1.1-7.3℃.Furthermore,its thermal conductivity is as low as 0.057 W/(m·K)and it has the potential of self-extinguishing(about 4s self-extinguishing after ignition),making it a promising thermal insulation material in some special environments.