Functional Materials from Lignin

The following sections are included:

• Preface
• About the Editors
• Acknowledgements
• Contents

Lignin is a class of complex organic polymers found in the structural tissues of plants. There are variations in the properties of lignin depending on its origin, such as polydispersity molar masses and hyperbranched structures. Lignin occurs via oxidative coupling of monolignols, which are synthesized via the phenylpropanoid pathway. To know the chemistry and structure of lignin is the first step in its valorization. In this chapter, we briefly describe the background, varieties, and complexity of the lignin and its structure. Moreover, the properties of lignin, including thermal properties, solubility, degradability, and antioxidant activities, have been discussed.

Lignin is the second most abundant terrestrial biopolymer after cellulose and is the largest renewable source of aromatic groups in nature. In this chapter, we present extraction methods and types of commercial-grade lignin from a raw biomass. A better understanding of types and production methods of lignin is an important starting point to study lignin as new materials, biofuel, and renewable sources of fine aromatic chemicals [1–3].

With the rapidly increasing demand for conventional petroleum-based polymers, exploration of biorenewable cellulosic materials as a low-cost and eco-friendly alternative to fossil polymers has witnessed great success. Lignin, the second most abundant natural polymer next to cellulose, is a byproduct in the pulp and paper industry that is obtained in large volumes every year; however, high-value lignin-based products are still sparsely used in many application. Recent advances revealed that lignin could act as an effective reinforcement in the polymer matrix due to its inherent properties. Various polar or non-polar lignins and their derivatives have been prepared via various methods, and the original lignin and its derivatives with different chemical structures have been applied to form miscible, partially immiscible or immiscible composites for specific applications. The chapter discusses lignin and its derivatives as UV-shielding/oxidant agents, thermal stabilizers and flame retardants in composites. More effort should be made to explore high-value functions of lignin and its derivatives as reinforcements in the polymer composites for practical application.

The intrinsic properties of raw lignin make it difficult to be used directly for advanced applications. To overcome these problems, there is a need to functionalize lignin and endow it with new chemical features. In this chapter, the well-established methods used to modify lignin are discussed, including fragmentation, modification of hydroxyl groups, introducing active sites, and chemical pre-treatment of lignin. These sophisticated lignin materials with diverse functions are further discussed in three active areas of application — polymeric composite toughening, healthcare and environment remediation. The opportunities and challenges and its indispensable role in the future of chemistry and polymer industries are also discussed.

Lignin is commonly found in plants as a part of the cell wall. Due to its high carbon content, lignin has the potential to be an alternative carbon precursor. Using lignin is more favourable than traditional precursors such as polyacrylonitrile (PAN) because of the low cost and since it also possesses comparable mechanical properties. In addition, it is easier to modify lignin, allowing for the easy development of various structures. In this hapter, we will discuss the use of lignin as a precursor along with the different methods of activation, including chemical and physical approaches, followed by its applications in carbon fibres and electronic devices due to its superior electrical conductivity. With these remarkable properties, lignin plays a crucial role for the future development of more advanced applications.

Green synthesis of nanomaterials is attracting more and more interest nowadays. The aggregation behavior of lignin can be used as a capping or reducing agent during the formation of lignin-mediated nanoparticles or lignin nanoparticles. Therefore, isolated lignin is useful in the field of nanotechnology. Lignin molecule contains functional groups such as thiols, aliphatic hydroxyl and phenolic hydroxyl, which could be used as secondary metabolites or reducing agents in the conversion of metal precursors into metal nanoparticles. Different approaches such as precipitation, dialysis and chemical modification were adopted for the preparation of lignin nanoscaled materials. The nanolignins were considered promising for various industrial applications such as in the fields of cosmetics, food and medicines.

Lignin is the main renewable source of aromatic structures on earth and plays a major role for the sustainable production of aromatic chemicals, monomers or building blocks which is with great potential to serve as raw materials for production of fuels, functional polymers and materials [1–3]. Because of its special aromatic structure, wide availability and easy modifications, lignin has promising applications such as adhesive, absorbents, carbon fibers in electrochemical filed and drug delivery materials. Also, the phenolics and polyphenols from lignin have beneficial therapeutic values, such as antioxidant, antimicrobial, antiinflammatory, cardio-protective, anticancerous, chemo-preventive and neuro-protective properties, which make it as huge attraction in life science. The aim of this chapter is to focus on and summarize industrial and medical applications of lignin lignin-based materials.

The following section is included:

• Index