Enhanced mechanical property and flame resistance of phosphorylated cellulose nanofiber based-aerogel combined with boric acid

As for cellulose-based aerogels, a feature of inadequate mechanics and easy-flammability seriously restricts their practical applications. To address this issue, herein a lightweight, mechanical elastic and flame-retardant phosphorylated lignin-based cellulose nanofiber (PLCNF-B) aerogel with the aid of boric acid was successfully obtained by freeze-drying method. Due to the uniform and tough network structure benefitting by strong hydrogen bond between phosphorylated fibers and boric acid, the resultant aerogel showed excellent mechanical performance, that is, high compressive strength of 8.9 kPa (strain: 50%) and outstanding cyclic reliability (remain 90% after 10 cycles). Meanwhile, PLCNF-B aerogel possesses highly improved flame-retardant property, that is, a high LOI value (up to 46%), significantly reduced peak heat release rate (11.2 W/g) and total heat release rate (0.47 kJ/g). Based on structural observation and analysis, the flame-retardant behavior should be attributed to the formation of PxOy/amorphous boron oxide protective layer, which is derived from the phosphorus containing group of PLCNF and boric acid. The splendid overall performance of aerogel material offers a potential material tactic for design and development of advanced bio-based aerogels for practical applications.