Valorization of energy crops as a source for nanocellulose production - Current knowledge and future prospects

Countless years of industrialization have led to the continuous depletion of nonrenewable resources and high levels of pollution. The overuse of nonrenewable resources has served as a motivation for intensive research and development of new types of green bio-based and degradable feedstocks derived from natural sources. Lignocellulosic biomass is one of the least used bio-resources in the world, consisting mainly of lignin, cellulose, and hemicelluloses. This type of biomass is plentiful in biopolymers in nature and is obtained from several sources, among which are the residues from agricultural and industrial lignocellulosic crops. The cellulose extracted from the biomass can be depolymerized giving rise to an extraordinary nanometer scale bio-based material. Abundance, biodegradability, renewability and low-cost, coupled with excellent mechanical properties appoint nanocellulose (NC) as one of the most promising nanometric biomaterials. In recent years, the improvement of the production processes, as well as the properties of the nanocellulose, has been extensively studied, thus exploring a range of applicability in diverse technological areas. Due to its mechanical properties, the reinforcement in polymeric bionanocomposites has been pointed out as one of the most interesting applications of the NC. This review focuses on the recent developments about the valorization of lignocellulosic biomass obtained from different lignocellulosic agro-industrial crops, as a source of NC, by discussing (i) structure and properties of lignocellulosic biomass (ii) promising eco-friendly biomass pre-treatment and nanocellulose production procedures, (iii) recent technological applications. Ultimately, the critical assessment of the current knowledge will allow the identification of prospects, limitations and future opportunities of this nanomaterial.