Synthesis, modification, and performance optimization of flame-retardant nanocellulose from waste cotton

Growing interest in renewable materials and sustainable processes has positioned cellulose nanocrystals (CNCs) as a key bio-based material due to their low density, high mechanical strength, thermal stability, and biodegradability, though their inherent flammability remains a limitation. In this study, waste cotton (WC) was used to produce CNCs, which were subsequently chemically modified and phosphorylated to develop flame-retardant nanocellulose (FR-NC). Structural and chemical analyses (FTIR, XPS, elemental analysis, and zeta potential) confirmed successful chemical modification and phosphorus incorporation, which influenced crystallinity and increased nanofiber diameter while retaining the cellulose I structure. The CNCs exhibited high zeta potential (>30 mV) and nanoscale diameters (<100 nm). Thermal analysis revealed enhanced stability and char-forming ability at 800 °C, with a 75% increase in the Limiting Oxygen Index (LOI). The CP 10 sample showed superior flame retardancy, with reduced self-ignition time (23 s), and higher LOI (32%) and char yield (88%) compared to CP 0 . The optimized FR-NC demonstrates strong potential as a sustainable reinforcement material for composites, electronics, and packaging applications. • Extracted pure cellulose from waste cotton and converted it into nanocrystal form. • Nanocrystal was modified through a highly concentrated alkali solution and phosphorylated with different ratios of phosphorus-containing compounds. • Optimize the performance of flame retardants and use them as fillers or reinforcements in structural composites, electronic items, floor coatings, and food packaging materials.