Valorization of endemic sigupai aceh rice husk as a renewable cellulose source for nanocellulose production via sulfuric acid hydrolysis

Endemic rice varieties can create locally abundant lignocellulosic residues. This study evaluates Sigupai rice husk, an Aceh endemic biomass, as a feedstock for cellulose nanocrystal production through alkaline delignification, hypochlorite bleaching and controlled sulfuric acid hydrolysis at 1, 2 and 3 mol/L. The work tests how increasing acid concentration affects yield, residual non-cellulosic material, crystallinity, surface chemistry and particle-size distribution. The products were assessed by gravimetry, moisture analysis, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray fluorescence, powder X-ray diffraction and dynamic light scattering particle-size analysis. Increasing the acid concentration increased recovered nanocellulose yield from 18.23 to 21.30%, decreased the XRF-derived residual fraction from 3.279 to 0.253%, and increased the apparent Segal crystallinity index from 91.26 to 99.34%, while reducing moisture content and the DLS-derived mean diameter from 43.31 to 5.27 nm. The calculated complementary XRF fraction increased from 96.721 to 99.747%, but this value is not interpreted as direct cellulose purity because XRF is an elemental technique. FTIR bands supported removal of non-cellulosic components and the appearance of sulfate-ester functionality. XRD remained cellulose-I-dominated, with possible cellulose-II-like features at 3 mol/L that require more rigorous phase analysis for confirmation. Because independent replicate extractions and complementary TEM/AFM, zeta-potential and thermal analyses were not available, the concentration-dependent trends are interpreted descriptively. These results support Sigupai rice husk as a local renewable feedstock and identify acid concentration as a practical processing variable for tuning measured nanocellulose properties.