Development and characterization of nanocellulose sheets from rice husk through sequential pretreatment and hydrolysis

Nanocellulose has emerged as a promising biomaterial owing to its exceptional mechanical strength, biodegradability, and wide industrial applicability. Rice husk, an abundant agro-waste rich in cellulose, hemicellulose, and lignin, represents an economical and sustainable feedstock for nanocellulose production. Rice husk was subjected to sequential pretreatment processes including hot water retting, caustic soda retting, acetic acid retting, alkaline treatment, and bleaching to progressively remove hemicellulose, lignin, and other impurities. The purified cellulose was further hydrolyzed with sulfuric acid to obtain nanocellulose, followed by repeated washing, centrifugation at 4000 rpm, and drying at 60 °C. The synthesized material was characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). Pretreatment steps effectively delignified rice husk and enriched the cellulose fraction, as evident from the progressive changes in fiber morphology. Sulfuric acid hydrolysis produced nanoscale cellulose fibrils, which aggregated into thin sheet-like structures upon drying. SEM micrographs revealed a dense fibrillar network with diameters ranging from 80 to 100 nm, while FTIR confirmed the retention of characteristic cellulose functional groups. EDX analysis showed elemental composition consistent with pure cellulose (C 54.52 wt%, O 45.48 wt%), verifying the high chemical purity of the synthesized nanocellulose. Furthermore, moisture uptake analysis revealed that nanocellulose exhibited significantly lower hygroscopicity compared with cellulose, confirming its superior dimensional stability under humid conditions. This study demonstrates a sustainable and efficient approach for converting rice husk into nanocellulose sheets through chemical pretreatment and controlled hydrolysis. The resulting nanocellulose possesses high purity and well-defined nanoscale morphology, highlighting its potential for applications in biopolymers, packaging, environmental remediation, and advanced material engineering.