High-Performance Materials from Bio-based Feedstocks. Группа авторов
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practicable, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment.
4 Designing Safer ChemicalsChemical products should be designed to effect their desired function while minimizing their toxicity.
5 Safer Solvents and AuxiliariesThe use of auxiliary substances (e.g. solvents, separation agents, etc.) should be made unnecessary wherever possible and innocuous when used.
6 Design for Energy EfficiencyEnergy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, synthetic methods should be conducted at ambient temperature and pressure.
7 Use of Renewable FeedstocksA raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable.
8 Reduce DerivativesUnnecessary derivatization (use of blocking groups, protection/deprotection, temporary modification of physical/chemical processes) should be minimized or avoided if possible because such steps require additional reagents and can generate waste.
9 CatalysisCatalytic reagents (as selective as possible) are superior to stoichiometric reagents.
10 Design for DegradationChemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment.
11 Real‐time Analysis for Pollution PreventionAnalytical methodologies need to be further developed to allow for real‐time, in‐process monitoring and control prior to the formation of hazardous substances.
12 Inherently Safer Chemistry for Accident PreventionSubstances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions, and fires. [6]
By examining the 12 principles of green chemistry, the use of waste biomass and bio‐based products to produce high‐performance materials is in agreement with the seventh principle, which encourages the use of renewable feedstocks. The utilization of renewable resources has an added benefit as they can potentially lead to the development of carbon‐neutral products.
According to the Kirk‐Othmer Encyclopedia of Chemical Technology, bio‐based materials refer to “products that mainly consist of a substance (or substances) derived from living matter (biomass) and either occur naturally or are synthesized, or it may refer to products made by processes that use biomass” [7]. Strictly speaking, this also includes traditional materials such as paper, leather, and wood, but these traditional uses are outside the scope of this book. It is important to note that bio‐based materials are different from biomaterials (which involve biocompatibility), and being bio‐based does not always mean the material will be biodegradable or safe.
The use of bio‐based materials seems to be an appropriate approach to minimize the negative impact on the environment while harnessing the unique properties they offer. The development application of high‐performance advanced bio‐based materials through green synthetic approaches (i.e. application of the 12 principles of green chemistry) can aid in developing sustainable circular economies, while still minimizing environmental impacts. High‐performance bio‐based materials can be applied in catalysis, energy materials, polymers, medical devices, and even construction materials to name but a few.
A significant source of biomass which is ripe for exploitation into high‐performance materials comes in the form of waste or agricultural residues. These include residues from food (e.g. corncob, sugarcane bagasse, rice husk, rice straw, and wheat straw) and non‐food production (e.g. cellulose and lignin), forest residues, industrial by‐products (e.g. ashes from biomass power generation), animal wastes (e.g. manure) as well as municipal wastes [7, 8]. These resources offer a complex mixture of polymers, inorganics, and chemicals, which can include but are not limited to polysaccharides, lignin, proteins, and ash, all of which are attractive alternative feedstocks to replace nonrenewable fossil‐based resources. Exhaustion of fossil fuels and other finite resources is a driver for bio‐based materials for high‐performance applications. The structural diversity of biomass constituents and their unique properties are also promising for new applications including high‐performance products.
Despite the great potential, some of the biggest challenges in using biomass as feedstock for high‐performance applications are its heterogeneity, seasonal variation, and complexity regarding separation. In many cases, biomass needs to undergo some form of processing prior to being used as high‐performance materials. Typically, the processing of biomass can be performed using chemical, biochemical, and thermochemical processes. These challenges are being tackled as part of the growth in holistic biorefineries, and such approaches that generate no waste are vital for maximizing the value of biomass.
However, unlike petrochemical feedstocks that require significant functionalization, bio‐based feedstocks are blessed with an abundance of functionalities. As such, the development of high‐performance materials from biomass requires different chemistries compared to those from fossil resources. The benefits of biomass utilization for industrial‐scale production of high‐performance materials are that they can potentially reduce waste and production costs, in addition to being carbon neutral, low cost, versatile, and renewable.
1.2 High‐performance Bio‐based Materials and Their Applications
Bio‐based materials can be synthesized directly from biomass constituents (such as polysaccharides and other polymers, proteins and amino acids, and active biological compounds) that are directly extracted from biomass, but also from biomass‐derived materials (e.g. bio‐derived polymers, porous carbons, or ashes) that require additional processing steps such as polymerization, carbonization, or combustion.
1.2.1 Biomass Constituents
1.2.1.1 Polysaccharides
Polysaccharides are biopolymers that are made up of monosaccharide units connected by glycosidic linkages. Polysaccharides can be obtained from plants (e.g. cellulose, starch, and pectin), algae (alginate), animals (chitin/chitosan), bacteria (bacterial cellulose), and fungi (pullulan). In contrast to synthetic polymers, polysaccharides are abundant in nature, renewable and biodegradable, and are therefore considered as promising replacements of nonrenewable fossil fuel‐based materials in a wide range of applications [9]. Yet, polysaccharides alone frequently present insufficient physicochemical properties, necessitating physical and/or chemical modifications to meet the required product specifications.
The hydrophilic nature of many polysaccharides presents a poor mechanical strength, which is a major hurdle for their widespread use. For this reason, polysaccharides are often blended with other polymers and/or chemically modified to improve their properties. In addition, inorganic additives can also play a key role to enhance materials properties from boosting strength to improving oxygen barrier and antibacterial properties. For example, esterification, etherification, acetylation, hydroxylation, and oxidation of starch, as well as the blending of starch with other biodegradable polymers can improve its physical and mechanical properties for food‐packaging applications (Chapter 15). Similarly, the substitution of hydrogen by alkyl groups to form cellulose ethers including ethyl cellulose (EC) and carboxymethyl cellulose (CMC) increases the hydrophobicity of cellulose. The addition of CMC into food packaging can improve mechanical, thermal, and barrier properties (Chapter 15). Although biopolymers account for less than 1% of the total plastic production [9], there is a strong growth potential toward their wider application driven by the circular economy trend. Novel biopolymers with improved properties and new functionalities for various applications such as packaging films and coatings as well as textile applications have been developed for commercialization and are reviewed in Chapter 15 with the emphasis on the packaging.
Similar modifications to the hydrophobicity of biopolymers have been used in coating materials