Starch, natural monomer

Generally, polymers from renewable resources have different origins such as natural (e.g., polysaccharides - namely cellulose and starch, which are produced in large amounts protein gums), synthetic (e.g., polylactic acid, PLA) derived from natural monomers, and microbial (e.g., polyhydroxybutyrate, PHB) [1, 5] The main components of biomass are cellulose, lignin, hemicelluloses and extractives and, as a nonwood structural component, starch. 

Polymers shown in Table 2.1 are synthetic polymers. However, there are several polymers that also occur naturally. The many known natural polymers include a few famous examples sueh as proteins, deoxyribonucleic acid (DNA), hemoglobin, insulin, starch, natural rubber etc. In order to xmderstand the polymeric nature of these natural substances let us look at proteins and see how they are built from simple monomers. 

Poly(lactic acid) (PLA) and starch are two promising candidates for biodegradable polymer blends since both materials are commercially available. PLA is a synthetic polymer produced from a natural monomer derived from starch, and of course starch is naturally abundant, which is derived from several plant forms [1-28],... 

The main raw material required for the production of viscose is ceUulose (qv), a natural polymer of D-glucose (Fig. 1). The repeating monomer unit is a pair of anhydroglucose units (AGU). CeUulose and starch (qv) are identical but for the way in which the ring oxygen atoms alternate from side to side of the polymer chain (beta linkages) in ceUulose, but remain on the same side (alpha linkages) in starch. 

By far the preponderance of the 3400 kt of current worldwide phenolic resin production is in the form of phenol-formaldehyde (PF) reaction products. Phenol and formaldehyde are currently two of the most available monomers on earth. About 6000 kt of phenol and 10,000 kt of formaldehyde (100% basis) were produced in 1998 [55,56]. The organic raw materials for synthesis of phenol and formaldehyde are cumene (derived from benzene and propylene) and methanol, respectively. These materials are, in turn, obtained from petroleum and natural gas at relatively low cost ([57], pp. 10-26 [58], pp. 1-30). Cost is one of the most important advantages of phenolics in most applications. It is critical to the acceptance of phenolics for wood panel manufacture. With the exception of urea-formaldehyde resins, PF resins are the lowest cost thermosetting resins available. In addition to its synthesis from low cost monomers, phenolic resin costs are often further reduced by extension with fillers such as clays, chalk, rags, wood flours, nutshell flours, grain flours, starches, lignins, tannins, and various other low eost materials. Often these fillers and extenders improve the performance of the phenolic for a particular use while reducing cost. 

Polymers are large, high molecular weight compounds formed by linking together many smaller compounds called monomers. The properties of the polymer are dependent on the monomer units used and the way in which they link together. Many polymers occur in nature such as cellulose, starch, cotton, wool, and rubber. Others are created synthetically, such as nylon, PVC, polystyrene, Teflon, and polyester. 

Macromolecules are found in nature. Cellulose, wool, starch, and DNA are but a few of the macromolecules that occur naturally. Carbons ability to form these large, complex molecules is necessary to provide the diversity of compounds needed to make up a tree or a human being. But many of the useful macromolecules that we use every day are created in the lab and industrial complex by chemists. Nylon, rayon, polyethylene, and polyvinyl chloride are all synthetic macromolecules. They differ by which repeating units (monomers) are joined together in the polymerization process. Our society has grown to depend on these plastics, these synthetic fabrics. The complexity of carbon compounds is reflected in the complexity of our modern society. 

Polyacrylamide shows many advantages over starch gel as a medium for high resolution electrophoresis and because of its synthetic nature its pore size can be more easily controlled. The gel is formed by the polymerization of the two monomers, acrylamide and a cross-linking agent, N, iV-methylene-bis-acrylamide (Figure 3.26). The proportion of the two monomers and not their total concentration is the major factor in determining the pore size, the latter having more effect on the elasticity and... 

Natural polymers are found in living things. For example, glucose, C6H12O6, is the monomer for the natural polymer starch. You will learn more about natural polymers later in this section. 

Bionolle is a typical biodegradable plastic. Currently, each raw material is made from petroleum, but we are developing more environmentally friendly green plastics. The first approach is to produce plastics from monomers such as succinic acid by biological methods. The second approach is to make hybrid compounds of Bionolle and natural resources like starch. The typical chain of materials for Bionolle is shown in Fig. 1. 

Some naturally occurring polymers such as cellulose, starch, wool, and silk are classified as condensation polymers, since one can postulate their synthesis from certain hypothetical reactants by the elimination of water. Thus cellulose can he thought of as the polyether formed by the dehydration of glucose. Carothers included such polymers by defining condensation polymers as those in which the formula of the repeating unit lacks certain atoms that are present in the monomer(s) from which it is formed or to which it may be degraded. In this... 

Already in 1955 Polymer Corporation (63) had applied for a patent on a process of treating naturally occurring polymeric substances or their derivatives with ozone containing inert gases and subsequently contacting the ozonized substrates with polymerizable monomers. In the presence of redox activators butadiene, acrylonitrile, and styrene were grafted onto cellulose, starch, casein, gelatin, and rubber. 

Polymers are large molecules formed by the repetitive bonding together of many smaller molecules, called monomers. As we ll see in the next chapter, biological polymers occur throughout nature. Cellulose and starch are polymers built from small sugar monomers, proteins are polymers built from amino acid monomers, and nucleic acids are polymers built from nucleotide monomers. The basic idea is the same, but synthetic polymers are much less complex than biopolymers because the starting monomer units are usually smaller and simpler. 

Polymers are large molecules (macromolecules) that consist of one or two small molecules (monomers) joined to each other in long, often highly branched, chains in a process called polymerization. Both natural and synthetic polymers exist. Some examples of natural polymers are starch, cellulose, chitin (the material of which shells are made), nucleic acids, and proteins. Synthetic polymers, the subject of this chapter, include polyethylene, polypropylene, polystyrene, polyesters, polycarbonates, and polyurethanes. In their raw, unprocessed form, synthetic polymers are sometimes referred to as resins. Polymers are formed in two general ways by addition or by condensation. 

Polymers are macromolecules built of smaller units called monomers. The process by which they are formed is called polymerization. They may be synthetic (nylon, Teflon, and Plexiglas) or natural (such as the biopolymers starch, cellulose, proteins, DNA, and RNA). Homopolymers are made from a single monomer. Copolymers are made from two or more monomers. Polymers may be linear, branched, or cross-linked, depending on how the monomer units are arranged. These details of structure affect polymers properties. 

One of the most abundant biopolymers available in nature is starch. Starch is a polysaccharide consistent of glucose monomers and is found in all green plants. Next to its occurrence in food and its use in food-related industries, the major application of starch is in the paper industry, followed by the adhesives industry. 

Carbohydrates would be the predominant raw materials for future biorefineries. The major polysaccharides found in nature are cellulose, hemicellulose and starch (see Chapter 1). These molecules would be mainly utilised after they are broken down to their respective monomers via enzymatic hydrolysis, thermochemical degradation or a combination of these two. Cellulose and hemicellulose, together with lignin, constitute the main structural components of biomass. Starch is the major constituent of cereal crops. This section would focus on the potential utilisation of carbohydrates and lignocellulosic biomass for chemical production. 

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