Harnessing Sargassum myriocystum as a sustainable source of cellulose nanocrystals: structural, thermal, and colloidal insights.

The environmental drawbacks of non-biodegradable plastics have sparked the demand for eco-friendly alternatives. This study focuses on the isolation and characterization of cellulose nanocrystals (CNCs) from the brown seaweed Sargassum myriocystum, a promising nanofiller. Cellulose was isolated from seaweed using alkali-bleaching treatments, then hydrolyzed using different concentrations of sulfuric acid to selectively remove amorphous regions, yielding CNCs. The cellulose yield was 33.78%, while the CNC yields ranged from 13.96- 14.41%. Characterization methods like FTIR, X-ray Diffraction(XRD), Thermogravimetric Analysis(TGA), and morphological studies through Scanning Electron Microscopy (SEM)and Transmission Electron Microscopy(TEM) identified the physical as well as chemical characteristics of the isolated products. The results highlighted that the CNCs exhibited high crystallinity, with crystallinity index increasing from 46.5% for cellulose to 78% for CNCs, indicating successful removal of amorphous regions and enrichment of crystalline domains. Thermal stability analysis revealed improved thermal properties after bleaching and hydrolysis of CNCs. The CNCs had a nano-sized, needle-like shape with an average length of 200-630 nm and width of 10-20 nm; forming stable suspension with zeta potential value of -37.5 mV,-21.6 mV,which are suitable for use as nanofillers in the development of materials and composites; enhancing mechanical and barrier properties. This work advances circular valorization of marine biomass.