Nanocellulose from agro-waste: a comprehensive review of extraction methods and applications

Agro-based wastes contain significant quantities of cellulosic materials from which nanocellulose can be extracted using various physical, biological, and chemical methods. These agro-wastes are termed lignocellulosic biomass as they contain cellulose, lignin and hemicellulose in abundance. Nanocellulose has its dimensions in nanoscale with excellent and distinctive attributes that attract researchers. Nanocellulose matrices are broadly categorised as nanocellulose crystals, nanocellulose fibrils and bacterial nanocellulose. Nanocellulose possesses some extremely significant properties, including biodegradability and biocompatibility, high aspect ratio, better mechanical attributes, easy surface modification, crystallinity, non-toxic nature, and water absorption capacity, making it a perfect material for a wide range of applications. The presence of hydroxyl groups on the surface of nanocellulose helps in its easier surface modification by various processes like carboxylation, silylation, esterification, amidation and etherification, which further allows its application as functional material. This review encompasses a brief discussion of the pre-treatments of lignocellulosic biomass, the different isolation processes of nanocellulose and the surface modification done to improve dispersibility in the polymer matrix. In this review, the different applications of nanocellulose in food industries, in biomedical and pharmaceutical fields, and their safety issues and toxicity to humans and the environment have also been briefly discussed.