Carboxymethyl cellulose from coconut fiber via sequential pretreatment.

The recalcitrant structure and high lignin content of coconut fiber limit its use as a raw material for synthesizing carboxymethyl cellulose (CMC). This study examined the application of sequential pretreatments, autohydrolysis, alkaline extraction, and organosolv (AH-AE-OG), to valorize coconut lignocellulosic biomass for producing CMC. The pretreatment process effectively removed hemicelluloses, reducing their content from 16.88% in untreated coconut fiber to 0.59% after AH-AE-OG and bleaching steps. Cellulose content increased from 42.09% in the untreated sample to 80.71% after AH-AE-OG and 86.13% following bleaching. The Kappa number decreased from 44.20 to 6.77, indicating lignin removal and a CMC yield of 38.05%. The TGA showed the expected mass loss for cellulose, and FTIR and SEM confirmed the presence of cellulose and the formation of CMC fibers, validating the effectiveness of the pre-treatment and chemical modification. These findings highlight the potential of sequential pretreatment to extract a high-quality cellulosic pulp and to produce CMF from coconut fiber. The proposed pretreatment process (AH-AE-OG) represents a potential innovation, as it employs a two-step methodology to eliminate hemicelluloses and partial lignin, followed by a third step characterized by high-efficiency lignin extraction and enhanced preservation of the cellulose structure, thereby facilitating improved conversion to CMC.