Characterization of nanocellulose extracted from short, medium and long grain rice husks

This study was designed with a hypothesis that morphological differences in plant parts of same origin could be governed by nano-scale constructional differences. Nanocellulose was extracted from husks of short, medium and long rice grains. Enhanced crystallinity and altered infrared diffraction indicated successful removal of noncellulosic amorphous and non-crystalline cellulose fractions during delignification and acid hydrolysis stages, respectively. Cellulose fibrils formed compact blocklets varying in size amongst the three husks as observed under SEM. Hydrolysis caused release of smooth surfaced cellulose nanowhiskers as observed under TEM and AFM. The nanowhiskers had different sizes (lengths = 55.7-178.6 nm, 111.2-476.7 nm and 153.1-778.9 nm; diameters = 11.7-28.9 nm, 16.1-37.5 nm and 19.9-48.3 nm), aspect ratio = 6.4, 9.8 and 16.9), crystallinity indices (58.82 %, 62.32 % and 76.69 %) and zeta potential (- 33.8 mV, - 27.1 mV and - 21.3 mV). Cellulose-I allomorphism with major XRD peaks at 2 theta = 16.3 degrees, 22.4 degrees and 34.5 degrees were not altered during extraction. Resistance of nanocelluloses to heat has higher than husks and celluloses. TGA curves of nanocellulose showed 3 step decomposition patterns against the typical 2 steps seen for husk and cellulose due to longer retention of low molecular weight carbonic residues in the former. Nano-scale construction of long husk was superior in size, crystallinity, strength and thermal stability, followed by medium and short husks. Nanocellulose samples had negligible toxicity (< 0.1 % hemolysis) against goat blood erythrocytes. The study suggested potential applicability of the extracted rice husk nanocelluloses as heat resistant materials and in food, cosmetic and pharmaceutical formulations.