Nitro-oxidation process for sustainable production of carboxylated lignin-containing cellulose nanofibers from sugarcane bagasse

This study demonstrated a sustainable, zero-waste approach to produce carboxylated lignin-containing cellulose nanofibers (LCNFs) directly from untreated sugarcane bagasse (SCB) using nitro-oxidation process (NOP) followed by high-pressure homogenization. Systematic optimization of reaction parameters was conducted, including reaction time, HNO-to-SCB ratio, HNO concentration, temperature, and co-oxidant addition (KNO₂). The results revealed that HNO concentration played the most dominant role in tailoring LCNF properties. Notably, the resulting LCNFs exhibited high dispersibility, with zeta potential values ranging from -38 to -65 mV due to the increasing surface carboxyl content (0.43 to 1.21 mmol/g) even under relatively mild conditions (e.g., 50 °C, 5 h). Lowering the acid concentration significantly increased the lignin content, enhancing the thermal stability. All LCNFs exhibited nanoscale diameters (7-13 nm), high crystallinity (54 to 70 %), and shear-thinning behavior. Elemental analysis of NOP effluents confirmed their enrichment with macro- and micro-nutrients, enabling their reuse as biofertilizers. This dual valorization of solid and liquid products positions NOP as a viable nanocellulose production and nutrient recovery pathway from lignocellulosic biomass. Resulting LCNFs, with their amphiphilic, biodegradable, and tunable surface properties, represent a compelling platform to make new materials to replace some synthetic polymers and reduce microplastic and chemical pollution.