Developing and Performance Optimizing of Flame‐Retardant Nanocellulose From Waste Rice Husk

ABSTRACT Cellulose nanofibers (CNFs) have attracted significant research interest owing to their remarkable features, including low density, outstanding durability, excellent thermal stability, large aspect ratio, extensive coverage and reactivity, eco‐friendliness, and biodegradability, although they are highly flammable. This research employed rice husks as a sustainable source to develop and optimize flame‐retardant nanocellulose (FR‐NC) using a phosphorylation‐based modification method. Comprehensive characterization and comparison were conducted on the surface chemistry, particle distribution, crystallization, thermal behavior, and flame‐retardant ability of the produced CNFs. The FTIR, XPS, elemental, and zeta potential investigations verified the bonding of phosphorus molecules on the CNF's surface. Phosphorylation affected crystallinity but still resulted in a larger nanofiber diameter. The findings showed that the primary chemical structure of cellulose was unaffected by phosphorylation. The resulting CNFs retained the cellulose I crystallographic shape and exhibited higher absolute zeta potentials (> 40 mV) and nanometric diameters (< 100 nm). Moreover, the developed CNFs exhibited improved thermal stability and higher char‐forming ability compared to crude cellulose at 800°C, along with a 70% increase in the limiting oxygen index (LOI) value. Furthermore, the addition of phosphate groups in CP 1 has also been shown to significantly increase flame retardancy, with less self‐ignition (26 s) and more char formation (89%) compared to CP 0 (237 s and 5%, respectively). Finally, FR‐NCs with different ratios of phosphorus‐containing compounds can find applications as fillers or reinforcements in structural composites, electronic items, floor coatings, and packaging materials.