Highly flame retardant, low thermally conducting, and hydrophobic phytic acid-guanazole-cellulose nanofiber composite foams

Cellulose as a bio-based material has attracted increasing attention due to its excellent properties. However, cellulose is very flammable and it is necessary to impart flame retardancy to cellulose nanofiber (CNF) foams. In this work, phytic acid (PA)-guanazole (GZ)-CNF composite foams were prepared by a simple freeze-drying method. SEM images indicated that the resultant PA-GZ-CNF composite foams exhibited a hierarchical porous structure. Moreover, the introduction of PA and GZ slightly affected the thermal conducting property of CNF foams. PA-GZ-CNF composite foams possessed excellent flame retardancy with a much higher LOI value and a UL-94 V-0 rating compared to that of pure CNF foams. Moreover, the peak of the heat release rate of PA-GZ-CNF composite foams exhibited a significant decrease from 57.80 to 29.27 kW/m2 and the total heat release declined from 2.10 to 1.21 MJ/m2. PA-GZ-CNF composite foams formed a protective char layer covered on the surface, which produced less thermal decomposition volatiles and prevented the spread of pyrolysis products into the gas phase. Additionally, PA-GZ-CNF composite foams achieved hydrophobicity with a water contact angle of 104.0° after hydrophobic treatment without sacrificing their flame retardancy.