From Pineapple Crown Waste to Functional Cellulose and Carboxymethylcellulose: Processing–Structure–Function Relationships for Circular Biorefinery Applications

Pineapple crown waste is a cellulose-rich residue generated along fresh-fruit and processing chains and is increasingly investigated as a feedstock for higher-value cellulosic materials. This review critically examines conversion of pineapple crown and related residues into cellulose, nanocellulose, carboxymethylcellulose (CMC), films, hydrogels, and agricultural materials through a processing–structure–function framework. Particular attention is given to alkaline delignification, oxidative bleaching, cellulose crystallinity and accessibility, carboxymethylation chemistry, and degree of substitution. Across the literature, greater process severity generally increases removal of non-cellulosic components, but does not invariably improve downstream functionality because excessive alkalinity, prolonged residence time, or intense bleaching can alter cellulose supramolecular organization and increase chemical consumption. Pineapple-derived CMC studies show that NaOH concentration, monochloroacetic acid dose, etherification temperature, and reaction time control substitution, solubility, rheology, and film-forming performance. Recent work further expands the field toward greener cellulose extraction, CMC films, high-substitution CMC, and seed-coating applications. Future process design should favor multicriteria optimization balancing delignification, cellulose accessibility, functional properties, reagent demand, solvent recovery, and end-use performance to support circular biorefineries for agricultural, packaging, environmental, and advanced-material applications.