Fundamentals of and advances in nanocellulose and nanochitin systems

Due to the deleterious environmental consequences resulting from a broad spectrum of synthetic polymers during use or post-application disposal, interest in biomaterials obtained from eco-friendly and sustainable sources is growing. This review first examines some of the fundamental concepts regarding biologically-derived nanoparticles ("bionanoparticles") extracted from the two most prevalent polymers on the planet: natural cellulose and chitin. With this background established, we turn our attention to several advances in this expanding field. Recent rheological studies have established that a "kink" often reported in steady-shear tests of fibrous nanocellulose suspensions is related to anisotropic flocs. Thorough analysis of this observation demonstrates the existence of dual yield points that pinpoint the processing conditions over which these flocs form. Another advance is isothermal titration calorimetry, which relates the formation of structure to viscous heating and provides a uniquely quick and precise analysis tool for measuring the concentration of cellulose nanocrystals responsible for the onset of mesomorphism in aqueous suspensions. In addition, the incorporation of various electrolytes in aqueous nanocellulose or nanochitin suspensions is capable of promoting cellulose or chitin nanocrystal (de)swelling or suspension templating of solid films, and positron annihilation lifetime spectroscopy can be used to follow changes in nanoscale free volume upon swelling in the presence of moisture, which can be independently used in conjunction with CO2-philic ionic liquids to achieve highly selective carbon capture in hybrid gas-separation membranes. (c) 2023 Kingfa Scientific and Technological Co. Ltd. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).