Multiple Cross‐Linking Framework of Dialdehyde Nanocellulose ( DAC )/Sodium Alginate ( SA ) Composite Aerogel and Its Flame Retardant Optimization Based on Phytic Acid Coordination

A dialdehyde nanocellulose (DAC)/sodium alginate (SA) composite aerogel was engineered around an orthogonal dual‐crosslinking architecture: a primary Schiff‐base network between DAC and polyethyleneimine‐modified ammonium polyphosphate (PAPP), and a secondary Fe 3+ coordination network with the carboxyl and phytate groups. The introduction of phytic acid enhanced the flame‐retardant system through N/P synergy. Tannic acid‐functionalized graphene oxide (TA/GO) was filled into the Schiff base network, effectively improving the sound absorption and flame‐retardant properties of the material. The resulting specimen excels in mechanical strength, achieving a compressive modulus of 36.99 kPa and a specific modulus of 3977.4 kPa·g −1 ·cm 3 at 60% compression, surpassing DAC/SA by 3.9 and 3 times, respectively. The prepared composite aerogel also achieved prominent flame‐retardant effects. It yielded a LOI of 37.4% and fulfilled the V‐0 rating standard in UL‐94 vertical flame tests, accompanied by 79.7% and 69.8% reduction in pHRR and THR. Further investigation revealed that the prepared composite aerogel demonstrated superior acoustic properties, with an NRC of 0.58 and an average sound absorption coefficient of 0.806, fully reaching the standard for high‐performance sound‐absorbing materials. These remarkable features enable the composite aerogel to be a competitive material for architectural fireproofing and noise reduction applications.