High-Performance Materials from Bio-based Feedstocks. Группа авторов
is the complex processing to obtain sufficient purity and quantity for the use in high‐performance products. Deep eutectic solvents (DES) comprise a class of solvents formed by eutectic mixtures of Lewis or Brønsted acids and bases, with physical properties similar to ionic liquids but different chemical properties [10]. These green solvents have the advantage over traditional ionic liquids since they are derived from biological resources and can be designed to have low toxicity and good biocompatibility. Chapter 6 of this book highlights a versatile approach of how biocompatible DES can be used as synthetic modifiers to achieve materials with a wide range of properties.
1.2.1.2 Other Biopolymers
Lignin is a three‐dimensional biopolymer composed of coniferyl alcohol, sinapyl alcohol, and p‐coumaryl alcohol monomers, but its specific structure and composition depend on the biomass [11]. A large number of hydroxyl groups in lignin provide a template for modification with specific functional groups. The ease and variability of lignin modification enable tailoring of the lignin structure to recover precious metals and rare earth metals (Chapter 7). Lignin has been used in fertilizer formulations, with the addition of plasticizers to improve the film‐forming properties (Chapter 16). Other applications of lignin are as binders in Li‐ion batteries (Chapter 5).
1.2.1.3 Proteins and Amino Acids
Proteins are biomolecules that are composed of amino acids and can be divided into plant‐based (e.g. soy protein, zein, and gliadin) and animal‐based proteins (e.g. gelatin, casein, and whey proteins). Plant proteins such as zein (extracted from maize) and gliadin (a component of gluten, extracted from wheat) are applied in the food industry as stabilizers of Pickering emulsions. However, pure protein emulsions are sensitive to changes in pH, which can be overcome by the formation of polymer‐biopolymer complexes. Zein nanoparticles can also be used to protect a hydrophobic core (such as vitamins) against oxidation and hydrolysis. Soy protein isolate, whey protein isolate, and casein are used in the formation of coacervates to encapsulate lipophilic‐active ingredients (Chapter 14). Gelatin, a natural water‐soluble protein obtained from collagen, is used in food‐packaging applications (Chapter 15).
Amino acids, the building blocks of proteins, and aliphatic diacids, like fumaric, glutaric, azelaic, and itaconic acids, have been used for the synthesis of MOFs with good water sorption and heat transfer applications (Chapter 12).
1.2.1.4 Active Biological Compounds
Apart from biopolymers and proteins, bio‐based resources may contain various active compounds that possess unique properties. Such high‐value chemicals may include fragrances, flavoring agents, and nutraceuticals like vitamins and antioxidants, and are generally extracted first before further processing of the biomass [12]. Naturally occurring fat‐soluble (A, D, E, and K) and water‐soluble vitamins (B and C) find applications in food. Here the key challenge is to retain the stability of the vitamins during storage and processing, which can be done by encapsulating the vitamin into delivery vesicles such as liposomes or coacervates (Chapter 14). Lecithins (such as phosphatidylcholine) and saponins (such as Quillaja saponins) are molecules with amphiphilic properties, which are used as natural surfactants to stabilize various vitamin‐containing emulsions (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