Although cellulose nanofiber (CNF) aerogels have promising applications in fields such as thermal insulation, adsorption, and separation, their use has been restricted because of their limited mechanical stability and flammability. To overcome these limitations, this study utilizes the unique properties of tannic acid (TA) and adenosine triphosphate (ATP) biomolecules to fabricate a synergistic TA/ATP/CNF aerogel with exceptional features such as ultralightness, hydrophobicity, lipophilicity, fire resistance, and high thermal insulation. With a low density of 6.13 mg·cm–3, thermal conductivity of 0.12 W·m–1·K–1, and high limiting oxygen index of 30.5%, the TA/ATP/CNF aerogel outperforms other state-of-the-art aerogels, including CNF-based aerogels. The study also presents a computational algorithm using Python 3.6 to analyze the aerogel's highly porous structure. Owing to its lipophilic properties, the TA/ATP/CNF aerogel is a promising porous adsorbent capable of rapidly adsorbing oil/organic solvents while exhibiting excellent flame retardancy, even when saturated with oil. This study highlights the potential of using natural biomolecules to improve the properties of CNF aerogels, making them suitable for various applications such as thermal insulation, adsorption, and separation.
Considering that fire safety is a persistent problem for most polymeric materials, including polyurethane (PU) foam, the demand for flame retardants (FRs) is growing. However, the use of conventional FRs containing halogenated and brominated chemicals has been continuously regulated owing to their toxicity. Here, we demonstrate the layer-by-layer (LbL) coating of negatively charged adenosine triphosphate (ATP) and positively charged chitosan (CS) as the synergistic FR on PU foam, a model flammable polymer material. The FR performance of the PU coated with LbL-assembled ATP and CS (ATP/CS-PU) was tested, and the results suggested that the ATP/CS layers were finely deposited on the surface of the PU without damaging the structure. Only five bilayers (5BL) were sufficient to impart excellent fire retardancy, which exhibited a limiting oxygen index value of 35% and the HF-1 rating in the UL94 foamed material horizontal burning test. In addition, ATP/CS(5BL)-PU showed a significant reduction in the peak heat release rate of 42.0% and in the total smoke release of 30.6% compared to that of bare PU (b-PU). Furthermore, the ATP/CS coatings did not deteriorate the mechanical properties of b-PU. Finally, combined thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) showed that ATP/CS(5BL)-PU was safe because it suppresses hazardous gases, which is the main problem with conventional FRs.
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