Rice husk nanocellulose: Extraction by high-pressure homogenization, chemical treatments and characterization

Rice husk is a substantial agricultural by-product of rice milling and has potential as a rich source of cellulose. This cellulose can be synthesized into nanocellulose materials. In this study, rice husk nanocellulose materials were synthesized by high-pressure homogenization (HPH) or acid hydrolysis (AH) combined with HPH (AH+HPH) treatments with different HPH cycles (6, 9 and 12 cycles at 120 MPa). Various physicochemical techniques were employed to investigate the nanocelluloses. It was found that the number of HPH cycles directly affected the particle size, crystallinity index and thermal stability of nanocellulose samples. The mean diameter and length of the nanocellulose were 10.15-12.42 nm and 602.13-620.08 nm for HPH samples and 11.94-12.34 nm and 436.22-440.04 nm for AH+HPH treatment. The crystallinity index of the nanocellulose ranged from 62% to 72%. Morphological characterization of nanocellulose treated with HPH and AH+HPH revealed the successful production of cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs). EDX analysis confirmed that the nanocellulose comprised 40.06-42.34% carbon and 50.07-54.56% oxygen as the main mineral elements. Therefore, this research offers an alternative strategy to enhance the value of rice husks and facilitate the utilization in the food system for future research.