Extraction of nanocellulose from natural sources: potential applications in a nanocomposite approach

Nanocelluloses (NC), including nanocrystalline cellulose, nanofibrillated cellulose and bacterial cellulose nanofibres, have become fascinating building blocks for the design of new biomaterials. Derived from the most abundant and renewable biopolymer, they are drawing a tremendous level of attention, which certainly will continue to grow in the future driven by the sustainability trend. This growing interest is related to their unsurpassed physical and chemical properties. Cellulose nanocrystals have been isolated from a variety of cellulosic sources, including plants, wastes, animals (tunicates), bacteria and algae, and in principle could be extracted from almost any cellulosic material. In practice, researchers have shown clear preferences. Commonly studied source materials have included wood, plants, and some kind of relatively pure cellulose such as microcrystalline cellulose or bleached Kraft pulp. Wood, owing to its natural abundance, is a key source of cellulose because of its widespread availability and high content of cellulose. At present, the research is focusing on the possible use of forest or agricultural residues as nanocellulose sources for their abundance at low economical and energetic cost, and for the simplified waste disposal. In the different climatic zones worldwide, various local sources are used for attempts of valorisation in this sense and, in some cases, technologies must be adapted to use certain sources. Over the last decades, major studies have shown that nanocellulose and especially cellulose nanocrystals, can be used as filler in nanocomposites to improve mechanical, thermal, optical and barrier properties of the selected polymer matrices. Incorporation of nanocelluloses into a wide range of polymers was attempted, including synthetic and natural ones (such as starch, poly (lactic acid), poly (hydroxybutyrate), etc.). Attention is increasingly devoted to fully bio-based and biodegradable systems, and ―green composites‖ is the term used to indicate composites with both polymeric matrix and filler being bio-based. Moreover, as more researchers from various scientific fields become interested in nanocellulose, other possible uses have been proposed and explored, such as foams, aerogels, building block for perm selective membranes, improvements in adhesive materials or adhesive by itself, use in lithium battery products as a mechanical reinforcing agent for low thickness polymer electrolytes. However, while a broad range of applications of NC exist, even if a high number of unknowns remain to be discovered. The aim of this chapter is to put in evidence the evolution and potentiality of emergent nanocellulose based nanocomposite approaches. Current research trends and a number of recent advances developed in our laboratories are reported and discussed