Wood Nanomaterials and Nanotechnologies

Abstract

Wood is an abundant, intrinsically renewable natural resource, with over three trillion mature trees on Earth that serve as an important carbon sink during growth. These features when combined with new technologies and processing techniques have endowed wood with rich, emerging functionality that make it a natural material choice toward sustainability. Around 300 million years of tree evolution has yielded over 60 000 woody species, each of which is an engineering masterpiece of nature. Evolution has led to wood's unique hierarchically porous structure, with cell walls primarily composed of cellulose, hemicellulose, and lignin, which can support trees 300 feet tall while also providing efficient water and nutrient transport. This lignocellulosic structure offers an intriguing material platform for diverse functionalization and applications. Recent research breakthroughs around the world epitomize the tremendous yet largely unexplored potential of such advanced wood-based functional materials—a paradigm shift from the conventional use of wood in furniture and building construction. Many efforts have been dedicated to tailoring wood's composition and structure at multiple length scales to impart new functionality and synthesize novel bio-based functional composites, which are explored in this special issue of Advanced Materials. Two major approaches, bottom-up and top-down, have been developed in fabricating wood-based functional materials. Most are made through bottom-up approaches that involve breaking down the cellulose fibers of wood into cellulose fibrils via a chemical and/or physical process and then assembling those building blocks into various macroscopic structures. Recently, the top-down approach, involving the structural and/or compositional engineering of wood without breaking the material down into its constituent fibrils, has gained increasing interest due to this strategy's capability to maintain wood's original anisotropic structure. Such top-down approaches have led to the invention of new wood-based functional materials with improved or even new properties and functions, largely expanding the application fields of wood. In addition to fabrication techniques, advanced wood materials have benefited from progress in wood characterization technologies and computational simulation methodologies. Characterization methods such as X-ray diffraction, X-ray tomography, Raman spectroscopy, electron microscopy, atomic force microscopy, nuclear magnetic resonance spectroscopy, and neutron diffraction enable the structures and behaviors of wood-based functional materials to be identified down to the micro- and nanoscale. Computational studies also play a key role in assisting and accelerating the discovery of mechanical, fluidic, ionic, electronic, optical, thermal, and acoustic properties in wood-based functional materials as well as determining important structure–property–function relationships that are essential for informing applied research. This special issue of Advanced Materials presents recent developments in wood nanomaterials and nanotechnologies toward various sustainable applications. In terms of wood nanomaterials and nanotechnologies, especially fabrication technologies, the past decade has witnessed great progress. Among the various fabrication technologies, bottom-up approaches have gained the most attention. Fuxiang Chu and co-workers (article number 2001135) present a comprehensive review on wood-derived functional polymeric materials fabricated by means of macromolecular engineering with a focus on the utilization of controlled/living polymerization, click chemistry, and dynamic bond chemistry for wood-based modification from the perspective of molecular design. Through a dissolving and regeneration process, regenerated cellulose can be made from wood, which can be further assembled into various macroscopic structures, such as macrofibers, films, hydrogels, and aerogels, as summarized by Lina Zhang and