Valorization of Gracilaria edulis for Cellulose Nanocrystal Production: Chemical Treatment, Morphology, and Crystallinity Analysis

Cellulose nanocrystals (CNCs) were extracted from the red macroalga Gracilaria edulis through sequential chemical treatments involving alkalization, bleaching, and acid hydrolysis. The progressive removal of non-cellulosic components resulted in a milky white, gel-like CNC suspension, indicating successful isolation. The structural and morphological properties of the obtained CNCs were examined using FTIR, SEM, and XRD techniques. FTIR spectra confirmed the presence of characteristic cellulose functional groups, including O-H, C-H, and C-O-C vibrations, demonstrating the effective purification of cellulose. SEM analysis revealed a clear transformation from aggregated fibrous structures to well-defined platelet-like nanocrystals at higher magnifications (up to 30,000X), confirming nanoscale morphology. XRD patterns exhibited prominent diffraction peaks corresponding to cellulose I, with a high crystallinity index of 91.3%, indicating efficient removal of amorphous regions during acid hydrolysis. Overall, the findings demonstrate that Gracilaria edulis is a promising and sustainable marine resource for producing highly crystalline cellulose nanocrystals suitable for advanced material applications.