rel="nofollow" href="#uc9d676ce-70b0-5ad3-9d15-241b94812a08">Chapter 14). Other active compounds include antioxidants, essential oils (e.g. oregano, thyme, clove, and cinnamon), and various extracts (e.g. from spent coffee grounds). Their incorporation into food packaging can prolong the shelf life of foods (Chapter 15).
1.2.2 Bioderived Materials
1.2.2.1 Polymers Derived from Biological Monomers
Polylactic acid (PLA) is a bio‐based thermoplastic composed of lactic acid monomers that are derived from renewable resources such as corn, sugarcane, or cassava. Due to its outstanding properties (biocompatible, biodegradable, and good mechanical strength), PLA and poly(lactic‐co‐glycolic) acid (PLGA) in biomedical applications such as anti‐HIV drug delivery, in the form of drug‐loaded nanoparticle formulations, topical products, and long‐acting inserts (Chapter 8). The good mechanical strength, optical transparency, biodegradability, and processability make PLA attractive for food‐packaging applications. A limitation of PLA is its poor impact force, which can be improved by addition of toughening agents [13]. Further modification of PLA can also improve properties such as antibacterial, antifogging, and gas barrier properties (Chapter 15).
Another interesting group of biomolecules is vegetable oils (VOs), which are composed of triglycerides from fatty acids. The VOs can be modified and used as monomers for the synthesis of alkyd resins and polyurethanes that find applications as coating materials in fertilizers (Chapter 16).
1.2.2.2 Carbon‐based Materials Derived from Biomass
After the extraction of valuable compounds, a significant proportion of the biomass remains with inferior composition and value. Or, in some cases, it may not be possible to extract valuables from the biomass due to, e.g. technical, financial, compositional, or hygienic reasons. Instead of leaving them to decay, these biomass feedstocks can be used as a carbon source to produce various carbon‐based materials. Carbon materials are inert, possess high mechanical stability, high surface area, and are chemically stable in the absence of oxygen under high or low pH. These properties make carbon materials appealing and suitable for various applications ranging from chemical sorbents, electrode materials, catalysts, and catalyst supports to slow‐release fertilizers [14–16].
Conversion of carbon‐rich biomasses can be carried out through thermochemical processes such as carbonization, pyrolysis, or similar techniques to produce porous carbons with tunable porosity. The porous structure can vary greatly depending on the cellulose content and source of the biomass as well as the pyrolysis conditions (e.g. temperature, atmosphere, duration, and presence of additives). The simplest form of porous carbon is biochar, which can directly be used as heterogeneous catalyst or catalyst support (Chapter 2). In soil, the porous biochar structure serves as a nutrient host to improve nutrient use efficiency. The water retention capacity, porosity, and high porous area of biochars can help slow down the nutrient release and thereby increase fertilizer use efficiency (Chapter 16).
Porous carbons can be categorized according to their pore size: microporous (<2 nm), mesoporous (2–50 nm), and microporous (>50 nm) [17]. High surface area and proper surface chemistry play a key role in catalysis and adsorption, and especially mesoporous carbons offer a wide range of applications. Most porous carbons, however, are microporous, allowing only small molecules or atoms to diffuse into the pore structure. Various activation techniques involving gases such as steam or CO2 (physical activation) or compounds such as KOH, H3PO4, or ZnCl2 (chemical activation) can be used to open the structure. The synthesis of porous carbons from various biomasses and the relations between synthesis conditions and material properties are discussed in detail in Chapter 2 for applications as catalyst or catalyst support, and in Chapter 4 for electrochemical applications.
Surface modification of porous carbons can be carried out to incorporate heteroatoms and functional groups through different methods including surface oxidation, halogenation, sulfonation, grafting, and impregnation [18]. Oxygen‐containing moieties such as carboxylic acids and phenolic hydroxyl groups have been successfully introduced onto the carbon surface via oxidative modification [18]. Apart from oxygen, also the incorporation of N‐, S‐, and P‐containing groups has been widely investigated. Sulfonation has been carried out to introduce –SO3H group to the porous structure, offering enhanced catalytic activity (Chapters 2 and 3). The incorporation of nitrogen‐containing pyridine‐N and pyrrole‐N into carbon electrodes improves the pseudocapacitance as well as catalytic activity for the oxygen reduction reaction in fuel cells (Chapter 4). The presence of phosphorus groups in biowastes can improve the pseudocapacitance of the carbon electrodes (Chapter 4).
Examples of other carbon materials that have been applied in energy storage applications include hard carbon, carbon nanofibers (CNFs), carbon nanotubes (CNTs), graphene, and carbon aerogels. Hard carbon can be produced from pyrolysis of biowastes such as fruit waste, sucrose, or glucose, and possesses a highly irregular and disordered carbon structure that make it a promising anode material for Na‐ion batteries [19]. The preparation of these carbons from biomass feedstocks and electrochemical applications are presented in Chapters 4 and 5. Production of biomass‐derived CNT and graphene and their catalytic performance are discussed in Chapter 2.
Starbon® is a special type of porous carbon with high mesoporosity, produced from polysaccharide hydrogels as structural templates. The relatively large pores (compared to the more traditional activated carbons) can effectively adsorb and desorb bulky molecules, showing promising applications as catalysts, catalyst supports, adsorbents, and recently as battery materials. Surface modification through sulfonation of Starbon® is very promising for catalysis applications. Chapter 3 highlights the synthesis and properties of (modified) Starbon® and its applications in adsorption and catalysis.
The versatility, environmental compatibility, and high availability are the driving forces for using bio‐ and agricultural wastes as starting materials of bio‐based carbon materials. For high‐performance applications, (modified) porous carbons have shown tremendous benefits and will continue developing to meet new application demands. Surface modification is necessary to fully exploit the potential of carbon materials. The challenges include the large‐scale yet well‐controlled and cost‐effective synthesis approaches. In addition, the inconsistency of the feedstocks and contamination may adversely affect the performance. Another concern is that biomass feedstock should not compete with food supply. Lignocellulosic biomass is particularly interesting for material development and plays an important role, both now and in the future.
1.2.2.3 Inorganic Materials Derived from Biomass
The elements C, O, H, and N generally
