Recent research progress on hairy cellulose nanocrystals: Preparation and applications

As one of the polysaccharide nanocrystals, cellulose nanocrystals (CNCs), also known as nanocrystalline cellulose (NCC), have been widely recognized due to their unique structures and versatile properties in both academic and industrial fields. Combining the green attributes of cellulose with nanoparticle characteristics, CNCs exhibit biodegradability, excellent mechanical properties, and large specific surface area. In contrast to CNCs obtained by conventional acid hydrolysis, hairy cellulose nanocrystals (HCNCs) with the length of about 100–200 nm and the width of about 5–13 nm are composed of central rigid nanorods and flexible hair-like cellulose molecular chains protruding from both ends. The preparation of HCNCs mainly involves processes such as periodate oxidation, chlorite oxidation, and hot-water treatment, resulting in the formation of hairs and high-contents of functional groups up to 6.6 mmol/g. These HCNCs have unique morphology and physicochemical properties, and they have shown broad application prospects, such as in the fields of flocculation, adsorption, scale inhibition, drug delivery, and sterilization. In this comprehensive viewpoint, we categorized HCNCs into three groups: cationic HCNCs (c-HCNCs), anionic HCNCs (a-HCNCs), and neutral HCNCs (n-HCNCs), according to their charges carried by various functional groups. Based on these three categorizations, we showed the various applications of HCNCs in a wide range of fields, and illustrated the structure–function-application relationship of HCNCs. The development of hairy cellulose nanocrystals is anticipated to significantly advance the frontiers of sustainable nanotechnology and renewable materials.