Emerging Nanotechnologies in Nanocellulose

This chapter first briefly discusses the current understanding of plant cell wall biosynthesis and cellulose ultra-structure prerequisites for understanding nanocellulose. From this fundamental understanding, the chapter is devoted to discussing conventional methods for producing two predominant types of cellulose nanomaterials (CNMs), namely cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs). Although many types of chemical treatments can deconstruct lignocellulose into nanoscale materials, mechanistic analyses based on the understanding of cell wall structure indicated that oxidation and acid hydrolysis are the most efficient approaches for producing CNMs from delignified wood pulp fibers. Some degree of delignification is necessary for producing CNMs from raw lignocellulose. Recent advances in achieving sustainable production of CNMs are also briefly mentioned. This chapter also briefly covers methods for characterizing various properties of CNMs.

This chapter discusses the top-down processing of nanocellulose materials and their potential applications in various fields. The hierarchically porous structure of biomass, the source material for producing top-down nanocellulose materials, is first introduced to provide basic understanding of its intrinsic structure. With such understanding, a variety of fabrication and modification strategies such as delignification, densification, patterning, surface functionalization and hybridization have been developed to tune the structure and properties of top-down nanocellulose materials. The rich tunability of structure and properties imparts these top-down nanocellulose materials with multiple functions for a wide range of applications in the fields of lightweight structural materials, thermal management, light management, water-energy technologies, electronics and so on. With advantageous features of inherited aligned structure, tunable structure and properties, improved performance and potentially low cost and environmental impacts, top-down nanocellulose materials have emerged as promising candidate of value-added sustainable materials for our society.

Bacterial nanocellulose (BNC) is an emerging nanomaterial that has drawn immense attention due to its unique physical and chemical properties. This chapter mainly focuses on the recent developments in the design, synthesis, and application of novel BNC-based multifunctional nanocomposites. The robust bio-mediated synthesis of nanocellulose network when combined with versatile in situ and post-modification strategies enables the incorporation of various functional nanomaterials into the nanocellulose network. These BNC-based multifunctional nanocomposites are highly promising for water treatment, energy harvesting, chemical sensing, catalysis, and life sciences. However, there are several outstanding challenges associated with BNC such as high production cost and durability that need to be addressed before these composites can be widely deployed in the real world. Despite the challenges, owing to their unique structure and properties, BNC-based nanocomposites will attract increased for various applications.

Nanocellulose aerogels have attracted attention in various fields because they have distinctive structures and properties, and are produced from abundant and sustainable precursors. In this chapter, we will summarize the development of aerogels using nanocellulose as a building block. First, we will describe the fabrication of nanocellulose aerogels by freeze-drying, supercritical drying, and atmospheric pressure drying methods. Then, we will discuss how to control the structures, properties, and functions of the aerogels via various strategies. Next, we will discuss the application of aerogels in energy storage, triboelectric nanogenerators, sensors, water purification, thermal insulation and scaffolds, according to the characteristics of the aerogels. Finally, we will describe the challenges and future trends associated with nanocellulose aerogels from our personal perspective.

The intrinsic mechanical properties of nanocellulose, with a specific stiffness and specific strength higher than most metals and alloys, are superior engineering materials. This makes the renewable yet abundantly available nanocellulose a promising material in multi-fold stimulating applications involving high strength and toughness. This chapter sheds light on the principle mechanistic design features leading to the superb mechanical properties in nanocellulose-based materials. Some of them, such as nanocellulose-based films, macrofibers, bulk wood and lightweight nanocomposites, are discussed. Different modeling approaches focusing on the underlying mechanism behind these fascinating mechanical properties are also reviewed. Finally, some broader future perspectives that can enrich this discipline are analyzed, which hopefully will stimulate the readers to explore the fertile opportunities of nanocellulose-based sustainable materials engineering in the foreseeable future.

Nanocellulose films are emerging as a natural and inexpensive optical material for advanced photonic applications such as optical sensors, photovoltaics, displays, and photocatalysis due to their ideal combination of environmental friendliness and unique optical properties (e.g., light transparency, tunable optical haze, selective reflection of left circularly polarized light, and iridescent appearance). The light scattering and light transparency of nanocellulose films and corresponding light management mechanisms are the focus of our chapter. We first introduce the design principles and theories for the light management of nanocellulose films in terms of the nature of light, structural hierarchy of cellulose, optical properties of multiscale cellulose, and structure of the nanocellulose film. Moreover, up-to-date strategies to manipulate their optical properties (light transmittance, transmission haze (light scattering), vivid structural coloration, circularly polarization, and bright whiteness) are highlighted. After that, we demonstrate their potential uses in various value-added photonic fields (e.g., optoelectronics and smart photonic applications) as photonic materials. Finally, some comments on technical and economic problems regarding nanocellulose films for photonic applications and their future development trends are provided.

Paper substrate made with nanocellulose is widely used to fabricate electronics by virtue of the superiorities of flexibility, lightweight, and eco-friendly, etc. Herein, advantages/limitations for nanocellulose paper as electronics substrate, electrodes design and fabrication on nanocellulose paper, and recent advances of various nanocellulose-based electronics, will be systematically reviewed and discussed to provide some insights and inspirations in developing paper electronics.

This chapter briefly explains the function of electrochemical energy storage devices, such as batteries and supercapacitors, and how nanocellulose can be used in the manufacturing of such devices. It is demonstrated that the use of nanocellulose facilitates the development of sustainable, versatile, and inexpensive electrochemical energy storage devices since nanocellulose can be used in the manufacturing of electrode materials, separators, and current collectors. Such nanocellulose-based energy storage devices can most likely be manufactured at low costs and may therefore serve as an interesting complement to conventional batteries and supercapacitors.

The emerging demand of ubiquitous smart electronics and the Internet of Things (IoT) calls for high-energy–density power sources with aesthetic versatility. Printed power sources have recently been in the spotlight as a promising system because of their various form factors and performance compatibility with electronics. Hence, extensive research on advanced materials has been conducted to achieve both facile processing and high performance of printed power sources. Cellulose, due to its natural abundance, environmental friendliness, chemical versatility, and dimensional stability, has been widely used as a reliable and sustainable basic constituent for a vast variety of materials/devices in our daily lives. The characteristic one-dimensional (1D) structure and chemical functionalities of cellulose bring unprecedented advantages to the fabrication and performance of energy storage materials and systems, which overcome the limitations of conventional synthetic materials. Notably, to obtain both form factor diversity and electrochemical reliability of printed power sources, cellulose has been extensively investigated as a promising building element because of its compatibility with the printing-based fabrications, mechanical stability, and electrochemically favorable morphology for printed power source components. In this chapter, we overview recent studies of cellulose as a building block for advanced printed energy storage systems, with a particular focus on application to printed electrodes, electrolytes/separator membranes, and substrates of Li-ion batteries/supercapacitors.

Water treatment, referring to the process that unwanted impurities (particles, oils, pathogens, organics, inorganics, etc.) are removed for improved water quality, is not only a cornerstone for human society and almost all industrial sectors but also crucial for sustainable development. Compared to energy-intensive thermal processing or petrochemical-derived materials that are currently deployed for water treatment, recent technological development has demonstrated the great potential of nanocellulose, a sustainable and the most abundant biopolymer on Earth, as the platform material for next-generation water treatment. This chapter provides a comprehensive overview of valorizing nanocellulose for water treatment through membrane filtration, absorption/adsorption, and solar-assisted water generation, with an emphasis on the surface modification, structural engineering, and/or composite techniques associated with these approaches. Opportunities and challenges are elaborated at the finishing part of the chapter to pave the road for future research.

Cellulose is the most abundant natural polymer on earth, providing a sustainable green resource that is renewable, degradable, biocompatible and cost-effective. The nanometer-sized cellulose, e.g. cellulose nanofibrils (CNFs) provides wide processing possibilities and greater application potential as a functional soft material building block. This chapter reviews a series of recent research from our group regarding the functionalization, fabrication, and assembly of CNFs aiming at triboelectric nanogenerator (TENG) development for mechanical energy harvesting. Specifically, TENG made from a flexible and compact CNF film with nanoscale surface roughness is introduced as a promising strategy for harvesting energy from footsteps. Chemical reaction approaches can be employed to introduce different functionalities thus different triboelectric polarities to CNFs, and thus significantly improve the TENG’s output. The output quantification and Figure of Merit (FOM) characterization are discussed in detail. Converting CNF films into conductive transparent films by aluminum-doped zinc oxide (AZO) coating is then reviewed. The mesoporous structure of the CNF film renders strong adhesion of the AZO layer and exhibits excellent mechanical integrity and electrical conductivity within a wide range of tensile and compressive strains, which provides a new transparent and degradable TENG material with decent output. At last, we briefly discuss the perspectives and opportunities of using CNFs as a new and potential functional soft material component in energy-related fields.

Nanocellulose having at least one dimension equal or less than 100 nm is the most abundant polymer on Earth. It is mainly obtained from the plants as well as produced by some microorganisms, algae, and animals, and synthetized in vitro by the cell-free enzyme systems. Over the past few decades, nanocellulose is receiving tremendous attention for its applications in different areas owing to its easy availability, renewability, and unique structural and chemical features, and inert and biocompatible nature. Taking the advantages of such features, the current biomaterials science aims at developing nanocellulose-based functional biomaterials with healing and regenerative properties, with the aim to meet the human demand, especially in tissue engineering and regenerative medicines. This chapter provides an overview of the synthesis of different types of nanocellulose, with special focus given to the development of nanocellulose-based functional biomaterials for various biomedical applications, including the synthetic organs, delivery systems, tissue regeneration materials, biosensors, and the biological scaffolds.