Example Cellulose

In plants, cellulose is synthesized by rosette terminal complexes (RTCs). The RTCs are hexameric protein structures containing the cellulose synthase enzyme. This enzyme synthesizes the individual cellulose chains. Each RTC is located at the interface of the cell membrane, similarly to the membrane-bound rubber transferase. Each RCT will polymerize a polysaccharide chain. This sounds a little bit complicated, but we are going to break down the synthesis into the 

FIGURE 5.14. Repeat unitin the ceiiuiose poiymer chain. 

Short oligosaccharide. siUMterol flips to cytosolic face 

FIGURE 5.19. Cellulose from com tree to building blocks (USDE public domain). 

Cellulolysis breaks down cellulose into smaller polysaccharides (cel-lodextrins) or into glucose units using glycoside hydrolase enzymes. These include endo-acting cellulases and exo-acting glucosidases. Such enzymes are usually secreted as part of multienzyme complexes. Cellulolysis is relatively difficult compared to the breakdown of other polysaccharides, due to the secondary/tertiary structure of cellulose. 

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Phloroglucinol is Hsted in the Colourindex as Cl Developer 19. It is particularly valuable in the dyeing of acetate fiber but also has been used as a coupler for azoic colors in viscose, Odon, cotton (qv), rayon, or nylon fibers, or in union fabrics containing these fibers (157). For example, cellulose acetate fabric is treated with an aromatic amine such as (9-dianisidine or a disperse dye such as A-hydroxyphenylazo-2-naphthylamine and the amine diazotizes on the fiber the fabric is then rinsed, freed of excess nitrite, and the azo color is developed in a phloroglucinol bath at pH 5—7. Depending on the diazo precursor used, intense blue to jet-black shades can be obtained with excellent light-, bleach-, and mbfastness. 

The life of membranes is affected by gradual chemical decomposition or change. For example, cellulose acetate membranes hydrolyze with time. 

Grafting reactions alter the physical and mechanical properties of the polymer used as a substrate. Grafting differs from normal chemical modification (e.g., functionalization of polymers) in the possibility of tailoring material properties to a specific end use. For example, cellulose derivatization improves various properties of the original cellulose, but these derivatives cannot compete with many of the petrochemically derived synthetic polymers. Thus, in order to provide a better market position for cellulose derivatives, there is little doubt that further chemical modification is required. Accordingly, grafting of vinyl monomers onto cellulose or cellulose derivatives may improve the intrinsic properties of these polymers. 

The intermolecular interactions stabilise the helices and greatly influence the properties of exopolysaccharides in solution, ie solubility, viscosity and gel-formation. A strong interaction or good-fit between molecules will lead to insolubility, whereas poor interaction will lead to solubility of exopolysaccharides. The interactions between molecules is influenced by the presence of side-chains. For example, cellulose is insoluble but introduction of a three monosaccharide side-chain into the cellulose chain gives the soluble xanthan. Small changes in the structure of the side-chains can alter the molecular interactions and thus properties of the exopolysaccharide. 

Orientation, wet stretching For plastics whose glass transition temperature (Tg) is above their decomposition temperature, orientation can be accomplished by swelling them temporarily with plasticizing liquids to lower their Tg of the total mass, particularly in solution processing. As an example, cellulose viscous films can be drawn during coagulation. Final removal of the solvent makes the orientation permanent. 

Thus polyacrylates tend to cross-link, while polymethacrylates tend to degrade, for example. Cellulosics also tend to degrade when irradiated. 

A proven solution to the binder problem is to use water insoluble organic polymer binders instead of clay. For example cellulose acetates and cellulose ethers binders are successfully employed to make commercial zeolitic adsorbents for sugar separation in aqueous solutions [154, 205, 218-223, 225-226, 231-232, 238]. This technique allows the use of zeoHte adsorbents in aqueous separation processes. 

In terms of function, polysaccharides fall into one of two groups structural and nutritional. For example, cellulose is a principal structural component of plants. Glycogen and starch, in contrast, are nutritional reservoirs for animals and plants, respectively. Monosaccharides may be mobilized from storage reservoirs such as glycogen and starch and then be metabolized to generate energy. 

Solid, for example cellulose fires involving material such as wood, paper, dust, etc. 

Borates are widely used in fire retardant applications. For example, cellulose insulation products used in homes and cotton batting used in mattresses and other furnishings are typically treated with boric acid to inhibit smoldering combustion. Borates are also used as fire retardants or fire retardant synergists in plastics, rubber products, and paints, where specialized borates such as zinc borate may be used. 

Polysaccharides Polysaccharides are composed of a huge number of monosaccharide units, and the number forming the molecule is often approximately known. For example, cellulose and starch are polysaccharides composed of hundreds of glucose units. 

The degradation of the cellulose fraction of the copolymer and subsequent recovery of the polyvinyl polymer have often been used to characterize the polymer. For example, cellulose may be acetylated and acid hydrolyzed to remove it from the copolymer. Then the recovered polymer can be dissolved, in solvent normally used for the polymer, and i the molecular weight of the polymer determined viscometrically (12, 42). As reported previously for polymers, such as polyacrylonitrile, a functional group on the polymer may be altered during the fractionating. These changes have been determined by infrared spectroscopy. For free-... 

Material natural and synthetic polymers, for example, cellulose acetate, silicone rubber, polyethylene... 

A large fraction of the chemical industry worldwide is devoted to polymer manufacture, which is very important in the area of hazardous wastes, as a source of environmental pollutants, in toxicology, and in the manufacture of materials used to alleviate environmental and waste problems. Synthetic polymers are produced when small molecules called monomers bond together to form a much smaller number of very large molecules. Many natural products are polymers for example, cellulose in wood, paper, and many other materials is a polymer of the sugar glucose. Synthetic polymers form the basis of many industries, such as rubber, plastics, and textiles manufacture. 

In micro- and ultrafiltrations, the mode of separation is by sieving through line pores, where microfiltration membranes filter colloidal particles and bacteria from 0.1 to 10 mm, and ultrafiltration membranes filter dissolved macromolecules. Usually, a polymer membrane, for example, cellulose nitrate, polyacrilonytrile, polysulfone, polycarbonate, polyethylene, polypropylene, poly-tretrafhioroethylene, polyamide, and polyvinylchloride, permits the passage of specific constituents of a feed stream as a permeate flow through its pores, while other, usually larger components of the feed stream are rejected by the membrane from the permeate flow and incorporated in the retentate flow [10,148,149],... 

Furthermore, crystalline polymers do obey the rules even at room temperature in so far as swelling behaviour is concerned. This again is a demonstration that crystalline regions serve as physical cross-links. Some crystalline polymers with strong hydrogen bonding groups can be made to dissolve at room temperature. But in these cases a very specific interaction between polymer and solvent must occur. For example, cellulose is soluble in 70% sulphuric acid and in aqueous ammonium thiocyanate nylon 6.6 is soluble in phenol and in a 15% calcium chloride solution in methanol. 

Microdialysis probes are now commercially available in various sizes, designs and materials. Microdialysis probes can be flexible for soft peripheral tissues and fluids or rigid for brain. Four probe geometries are available linear, loop, side-by-side and concentric. The semipermeable membrane is generally chosen as long as possible, typically between 1 and 10 mm. The probe radius is generally chosen as small as possible, typically between 200 and 400 im O.D. to cause minimal disturbances within the tissue. Dialysis probes are made of various materials (for example celluloses and copolymers like polyacetonitrile/sodium methallyl sulfonate and polycarbonate/ether). The molecular mass cut off (5-50 kDa), inertness and permeability to solutes of the probes could be different. 

Cellulose can also be esterified by aromatic acids. However, derivatives of any importance are only the cellulose cinnamic and salicylic acid esters. A number of nitrogen-containing esters are also known, for example, cellulose dialkyl di ami noacetate, cellulose acetate-N,N-dimethylaminoacetate, and cellulose propionate-3-morpholine butyrate. Because of the presence of basic substituents these derivatives, although water insoluble, can be dissolved in acidic solutions. Such derivatives have found use as surface coatings in photographic films and in tablets for pharmaceutical purposes. 

While some of the above can occur with cellulose treated with the alkaline earth hydroxides or carbonates, their tendency to insolubilize compounds with carboxyl groups will work against swelling and the increase in accessibility. For example, cellulose oxidized with N204 swells and dissolves in sodium hydroxide but is not soluble in lime solution. 

Q7 Fibre comes from the parts of plants which cannot be digested in the human gut. It may either be insoluble, for example cellulose, hemicellulose or lignins, or the soluble type, such as pectins and gums. The soluble type of fibre helps to slow absorption of cholesterol from the gut, lowers blood cholesterol and decreases the risk of coronary disease. 

Western diets are generally high in refined foods and low in fibre content. Fibre may be insoluble, for example cellulose, or soluble, for example pectin from plants. Insoluble fibre binds water, increases the bulk of the faeces and increases rapidity of transit through the intestine. Soluble fibre slows absorption of cholesterol and reduces blood cholesterol concentration. 

Fibre is a polymer carbohydrate. Most fibre is derived from the cell walls of plants and is indigestible, for example cellulose. 

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