Amino-modified cellulose nanocrystals with adjustable hydrophobicity from combined regioselective oxidation and reductive amination

Abstract

The controlled revision of surface properties to alter the hydrophobic features of nanocellulose is a potential technique to obtain materials for many novel applications and to replace oil-based materials acting as amphiphilic polyelectrolytes, among others. In this study, linear amines with increasing chain length were used to adjust the hydrophobicity of amphiphilic cellulose nanocrystals (CNCs). Methyl-, ethyl-, n-propyl-, n-butyl-, n-pentylamine, and n-hexylamine were introduced into a cellulose backbone using combined periodate oxidation and reductive amination in an aqueous environment. A high-pressure homogenizer was used to liberate a highly transparent (over 85% at visible light range) nanocrystal dispersion containing CNCs with a length of 73-131 nm and a width of 5-6 nm. All of the CNCs had similar charge density but the hydrophobicity, indicated by the contact angle measurement from the films, increased gradually from 64° to 109° as a function of amine chain length. Thus, this study demonstrated the fabrication of uniform, amphiphilic nanosized polyelectrolytes with modifiable hydrophobicity.

Keywords: 2-Picoline borane (PubChem CID: 7975); Amylamine (PubChem CID: 8060); Cellulose nanocrystals; Ethylamine hydrochloride (PubChem CID: 11198); Hydrophobicity; Lithium chloride (PubChem CID: 433294); Methylamine hydrochloride (PubChem CID: 6364545); Modifiable properties; Periodate oxidation; Reductive amination; Sodium periodate (PubChem CID: 23667635); n-Butylamine hydrochloride (PubChem CID: 6432400); n-Hexylamine hydrochloride (PubChem CID: 67342); n-Porpylamine hydrochloride (PubChem CID: 11165).