1.
Chemical process
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In a scientific sense, a chemical process is a method or means of somehow changing one or more chemicals or chemical compounds. Such a chemical process can occur by itself or be caused by an outside force, neither of these definitions is exact in the sense that one can always tell definitively what is a chemical process and what is not, they are practical definitions. There is also significant overlap in these two definition variations, because of the inexactness of the definition, chemists and other scientists use the term chemical process only in a general sense or in the engineering sense. However, in the sense, the term chemical process is used extensively. The rest of the article will cover the type of chemical process. Although this type of process may sometimes involve only one step, often multiple steps. In a plant, each of the unit operations commonly occur in individual vessels or sections of the plant called units, often, one or more chemical reactions are involved, but other ways of changing chemical composition may be used, such as mixing or separation processes. The process steps may be sequential in time or sequential in space along a stream of flowing or moving material, see Chemical plant. For a given amount of a material or product material. These amounts can be scaled up or down to suit the desired capacity or operation of a chemical plant built for such a process. More than one plant may use the same chemical process. Chemical processes like distillation and crystallization go back to alchemy in Alexandria, such chemical processes can be illustrated generally as block flow diagrams or in more detail as process flow diagrams. Block flow diagrams show the units as blocks and the streams flowing between them as connecting lines with arrowheads to show direction of flow, unit processing is the basic processing in chemical engineering. Together with unit operations it forms the main principle of the chemical industries. Each genre of unit processing follows the same chemical law much as each genre of unit operations follows the physical law
2.
Polymer
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A polymer is a large molecule, or macromolecule, composed of many repeated subunits. Because of their range of properties, both synthetic and natural polymers play an essential and ubiquitous role in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure, Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. The units composing polymers derive, actually or conceptually, from molecules of low molecular mass. The term was coined in 1833 by Jöns Jacob Berzelius, though with a distinct from the modern IUPAC definition. The modern concept of polymers as covalently bonded macromolecular structures was proposed in 1920 by Hermann Staudinger, Polymers are studied in the fields of biophysics and macromolecular science, and polymer science. Polyisoprene of latex rubber is an example of a polymer. In biological contexts, essentially all biological macromolecules—i. e, proteins, nucleic acids, and polysaccharides—are purely polymeric, or are composed in large part of polymeric components—e. g. Isoprenylated/lipid-modified glycoproteins, where small molecules and oligosaccharide modifications occur on the polyamide backbone of the protein. The simplest theoretical models for polymers are ideal chains, Polymers are of two types, Natural polymeric materials such as shellac, amber, wool, silk and natural rubber have been used for centuries. A variety of natural polymers exist, such as cellulose. Most commonly, the continuously linked backbone of a used for the preparation of plastics consists mainly of carbon atoms. A simple example is polyethylene, whose repeating unit is based on ethylene monomer, however, other structures do exist, for example, elements such as silicon form familiar materials such as silicones, examples being Silly Putty and waterproof plumbing sealant. Oxygen is also present in polymer backbones, such as those of polyethylene glycol, polysaccharides. Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain or network, during the polymerization process, some chemical groups may be lost from each monomer. This is the case, for example, in the polymerization of PET polyester, the distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue. Laboratory synthetic methods are divided into two categories, step-growth polymerization and chain-growth polymerization. However, some methods such as plasma polymerization do not fit neatly into either category
3.
Sulfur
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Sulfur or sulphur is a chemical element with symbol S and atomic number 16. It is abundant, multivalent, and nonmetallic, under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a yellow crystalline solid at room temperature. Chemically, sulfur reacts with all elements except for gold, platinum, iridium, tellurium, though sometimes found in pure, native form, sulfur usually occurs as sulfide and sulfate minerals. Being abundant in native form, sulfur was known in ancient times, being mentioned for its uses in ancient India, ancient Greece, China, in the Bible, sulfur is called brimstone. Today, almost all elemental sulfur is produced as a byproduct of removing sulfur-containing contaminants from natural gas, the greatest commercial use of the element is the production of sulfuric acid for sulfate and phosphate fertilizers, and other chemical processes. The element sulfur is used in matches, insecticides, and fungicides, many sulfur compounds are odoriferous, and the smells of odorized natural gas, skunk scent, grapefruit, and garlic are due to organosulfur compounds. Hydrogen sulfide gives the characteristic odor to rotting eggs and other biological processes, sulfur is an essential element for all life, but almost always in the form of organosulfur compounds or metal sulfides. Three amino acids and two vitamins are organosulfur compounds, many cofactors also contain sulfur including glutathione and thioredoxin and iron–sulfur proteins. Disulfides, S–S bonds, confer mechanical strength and insolubility of the keratin, found in outer skin, hair. Sulfur is one of the chemical elements needed for biochemical functioning and is an elemental macronutrient for all organisms. Sulfur is derived from the Latin word sulpur, which was Hellenized to sulphur, the spelling sulfur appears toward the end of the Classical period. In 12th-century Anglo-French, it was sulfre, in the 14th century the Latin ph was restored, for sulphre, the parallel f~ph spellings continued in Britain until the 19th century, when the word was standardized as sulphur. Sulfur was the form chosen in the United States, whereas Canada uses both, the IUPAC adopted the spelling sulfur in 1990, as did the Nomenclature Committee of the Royal Society of Chemistry in 1992, restoring the spelling sulfur to Britain. Sulfur forms polyatomic molecules with different chemical formulas, the best-known allotrope being octasulfur, cyclo-S8. The point group of cyclo-S8 is D4d and its dipole moment is 0 D. Octasulfur is a soft, bright-yellow solid that is odorless and it melts at 115.21 °C, boils at 444.6 °C and sublimes easily. At 95.2 °C, below its melting temperature, cyclo-octasulfur changes from α-octasulfur to the β-polymorph, the structure of the S8 ring is virtually unchanged by this phase change, which affects the intermolecular interactions. At higher temperatures, the viscosity decreases as depolymerization occurs, molten sulfur assumes a dark red color above 200 °C
4.
Cross-link
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A cross-link is a bond that links one polymer chain to another. They can be covalent bonds or ionic bonds, polymer chains can refer to synthetic polymers or natural polymers. When the term cross-linking is used in the synthetic polymer science field, cross-linking is used in both synthetic polymer chemistry and in the biological sciences. Although the term is used to refer to the linking of polymer chains for both sciences, the extent of crosslinking and specificities of the crosslinking agents vary. Of course, with all science, there are overlaps, when cross links are added to long rubber molecules, the flexibility decreases, the hardness increases and the melting point increases as well. When polymer chains are linked together by cross-links, they some of their ability to move as individual polymer chains. How the crosslinking process works and how it improves the properties of polymers is nicely illustrated in this video-animation, for example, a liquid polymer can be turned into a solid or gel by cross-linking the chains together. In polymer chemistry, when a polymer is said to be cross-linked. The resulting modification of mechanical properties depends strongly on the cross-link density, low cross-link densities decrease the viscosities of polymer melts. Intermediate cross-link densities transform gummy polymers into materials that have elastomeric properties, very high cross-link densities can cause materials to become very rigid or glassy, such as phenol-formaldehyde materials. Cross-links can be formed by reactions that are initiated by heat, pressure, change in pH. For example, mixing of an unpolymerized or partially polymerized resin with specific chemicals called crosslinking reagents results in a reaction that forms cross-links. Cross-linking can also be induced in materials that are normally thermoplastic through exposure to a source, such as electron beam exposure, gamma-radiation. For example, electron beam processing is used to cross-link the C type of cross-linked polyethylene, the chemical process of vulcanization is a type of cross-linking that changes rubber to the hard, durable material associated with car and bike tires. This process is often called sulfur curing, the term comes from Vulcan. This is, however, a slower process, a typical car tire is cured for 15 minutes at 150 °C. However, the time can be reduced by the addition of such as 2-benzothiazolethiol or tetramethylthiuram disulfide. Both of these contain an atom in the molecule that initiates the reaction of the sulfur chains with the rubber
5.
Vulcanized fibre
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Vulcanized fibre is a laminated plastic composed of only cellulose. The material is a tough, resilient, hornlike material that is lighter than aluminium, tougher than leather, the newer wood-laminating grade of vulcanized fibre is used to strengthen wood laminations used in skis, skateboards, support beams and as a sub-laminate under thin wood veneers. A product very similar to vulcanized fibre is leatheroid, leatheroid, however, is made using a different chemical process. The British patent for vulcanized fibre was obtained in 1859 by the Englishman Thomas Taylor and he gained the patent after the introduction of celluloid in 1856 and before the invention of viscose rayon in 1894. In 1871 Thomas Taylor obtained the United States Patent for vulcanized fibre, the first N. Y. corporation was also found in the 1873 N. Y. City Directory which also listed William Courtenay President and Charles F. Cobby Secretary in 1873, from 1873 until 1878 the Vulcanized Fiber Co. had a New York office address of 17 Dey St. while the factory was located in Wilmington Delaware. This can be seen in the advertisements that were placed in different publications at this time in history. A special charter was granted by the state of Delaware in 1873 until the Delaware corporation was incorporated on February 8,1875 which now listed William Courtenay President and Clement B. In 1884 Courtenay & Trull Co, N. Y. was merged into the Vulcanized Fibre Co. which gave the company control over a new invention called by the trade name Gelatinized Fibre. And the Laminar Fibre Company of North Cambridge, Mass, in 1922 the name was changed again when it was directly purchased by the National Fibre & Insulation Company of Yorklyn Delaware. The president of the National Fibre Company at this time was J. Warren Marshall, in 1965 the name was changed again to the NVF Company in order to avoid confusion over the years with a new and changing product line. The water power of the Piedmont streams in Northern Delaware led to a proliferation of companies in the vulcanized fibre business, over the years, these companies reorganized and merged. Diamond State Fibre Co. and Franklin Fibre Company, in the 1965 Post’s Pulp and Paper Directory, National Vulcanized Fibre Co. was listed as having two mills producing rag paper for vulcanized fibre. They were at Newark, producing 15 tons a day, and Yorklyn and this compares with Spaulding Fibre’s Tonawanda plant, then producing 40 tons a day. The competitors also produced bakelite, but marketed them under different names, Spaulding’s was Spauldite and National’s brand was Phenolite, the process started with paper made from cotton rags. Before the processing of wood pulp and chemical wood pulps in the mid-19th century, the cotton rag sheet produced for conversion to vulcanized fibre is made like a sheet suitable for saturating. A paper is made for saturating by omitting any sizing additive, today most paper sheets made for writing, printing, and coating have internal sizing provided by rosin, alkyl succinic anhydride, or alkyl ketene dimer and surface sizing provided by starch. A sheet made for saturating would have none of those chemical ingredients, the unsized saturating cotton fibre paper prepared for vulcanized fibre would be passed through a vat containing a zinc chloride solution
6.
Cellulose
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Cellulose is an organic compound with the formula n, a polysaccharide consisting of a linear chain of several hundred to many thousands of β linked D-glucose units. Cellulose is an important structural component of the cell wall of green plants, many forms of algae. Some species of bacteria secrete it to form biofilms, Cellulose is the most abundant organic polymer on Earth. The cellulose content of cotton fiber is 90%, that of wood is 40–50%, Cellulose is mainly used to produce paperboard and paper. Smaller quantities are converted into a variety of derivative products such as cellophane. Conversion of cellulose from energy crops into biofuels such as ethanol is under investigation as an alternative fuel source. Cellulose for industrial use is mainly obtained from wood pulp and cotton, some animals, particularly ruminants and termites, can digest cellulose with the help of symbiotic micro-organisms that live in their guts, such as Trichonympha. In humans, cellulose acts as a bulking agent for feces and is often referred to as a dietary fiber. Cellulose was discovered in 1838 by the French chemist Anselme Payen, Cellulose was used to produce the first successful thermoplastic polymer, celluloid, by Hyatt Manufacturing Company in 1870. Production of rayon from cellulose began in the 1890s and cellophane was invented in 1912, hermann Staudinger determined the polymer structure of cellulose in 1920. The compound was first chemically synthesized in 1992, by Kobayashi, Cellulose has no taste, is odorless, is hydrophilic with the contact angle of 20–30 degrees, is insoluble in water and most organic solvents, is chiral and is biodegradable. It was shown to melt at 467 °C in 2016 and it can be broken down chemically into its glucose units by treating it with concentrated mineral acids at high temperature. Cellulose is derived from D-glucose units, which condense through β-glycosidic bonds and this linkage motif contrasts with that for α-glycosidic bonds present in starch and glycogen. This confers tensile strength in cell walls, where cellulose microfibrils are meshed into a polysaccharide matrix, compared to starch, cellulose is also much more crystalline. Whereas starch undergoes a crystalline to amorphous transition when heated beyond 60–70 °C in water, cellulose requires a temperature of 320 °C, several different crystalline structures of cellulose are known, corresponding to the location of hydrogen bonds between and within strands. Natural cellulose is cellulose I, with structures Iα and Iβ, Cellulose produced by bacteria and algae is enriched in Iα while cellulose of higher plants consists mainly of Iβ. Cellulose in regenerated cellulose fibers is cellulose II, the conversion of cellulose I to cellulose II is irreversible, suggesting that cellulose I is metastable and cellulose II is stable. With various chemical treatments it is possible to produce the structures cellulose III, many properties of cellulose depend on its chain length or degree of polymerization, the number of glucose units that make up one polymer molecule
7.
Zinc chloride
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Zinc chloride is the name of chemical compounds with the formula ZnCl2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white, ZnCl2 itself is hygroscopic and even deliquescent. Samples should therefore be protected from sources of moisture, including the water present in ambient air. Zinc chloride finds wide application in textile processing, metallurgical fluxes, no mineral with this chemical composition is known aside from the very rare mineral simonkolleite, Zn58Cl2·H2O. Four crystalline forms of ZnCl2 are known, α, β, γ, and δ, here, a, b, and c are lattice constants, Z is the number of structure units per unit cell and ρ is the density calculated from the structure parameters. Rapid cooling of molten ZnCl2 gives a glass, the covalent character of the anhydrous material is indicated by its relatively low melting point of 275 °C. Further evidence for covalency is provided by the solubility of the dichloride in ethereal solvents where it forms adducts with the formula ZnCl2L2. In the gas phase, ZnCl2 molecules are linear with a length of 205 pm. Molten ZnCl2 has a viscosity at its melting point and a comparatively low electrical conductivity that increases markedly with temperature. A Raman scattering study of the melt indicated the presence of polymeric structures, five hydrates of zinc chloride are known, ZnCl2n where n =1,1.5,2.5,3 and 4. The tetrahydrate ZnCl24 crystallizes from solutions of zinc chloride. Anhydrous ZnCl2 can be prepared from zinc and hydrogen chloride, Zn +2 HCl → ZnCl2 + H2 Hydrated forms and aqueous solutions may be readily prepared similarly by treating Zn metal with hydrochloric acid. Commercial samples of zinc chloride typically contain water and products from hydrolysis as impurities, such samples may be purified by recrystallization from hot dioxane. Anhydrous samples can be purified by sublimation in a stream of hydrogen chloride gas, finally, the simplest method relies on treating the zinc chloride with thionyl chloride. Molten anhydrous ZnCl2 at 500–700 °C dissolves zinc metal, and, on cooling of the melt, a yellow diamagnetic glass is formed. A number of containing the tetrachlorozincate anion, ZnCl2−4, are known. Caultons reagent, V2Cl36Zn2Cl6 is an example of a salt containing Zn2Cl2−6, the compound Cs3ZnCl5 contains tetrahedral ZnCl2−4 and Cl− anions. No compounds containing the ZnCl4−6 ion have been characterized, whilst zinc chloride is very soluble in water, solutions cannot be considered to contain simply solvated Zn2+ ions and Cl− ions, ZnClxH2O species are also present
8.
Thermoplastic
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A thermoplastic, or thermosoftening plastic, is a plastic material, a polymer, that becomes pliable or moldable above a specific temperature and solidifies upon cooling. Most thermoplastics have a molecular weight. The polymer chains associate through intermolecular forces, which weaken rapidly with increased temperature, thermoplastics differ from thermosetting polymers, which form irreversible chemical bonds during the curing process. Thermosets do not melt, but decompose and do not reform upon cooling, above its glass transition temperature and below its melting point, the physical properties of a thermoplastic change drastically without an associated phase change. Some thermoplastics do not fully crystallize below the transition temperature. Amorphous and semi-amorphous plastics are used when high optical clarity is necessary, amorphous and semi-amorphous plastics are less resistant to chemical attack and environmental stress cracking because they lack a crystalline structure. Brittleness can be decreased with the addition of plasticizers, which increases the mobility of amorphous chain segments to effectively lowers the transition temperature. Modification of the polymer through copolymerization or through the addition of side chains to monomers before polymerization can also lower it. Naval Research Laboratory developed thermoplastic armor, that can be repaired in the field by a user via tools for pressing irons, acrylic, a polymer called poly, is also known by trade names such as Lucite, Perspex and Plexiglas. It serves as a substitute for glass for items such as aquariums, motorcycle helmet visors, aircraft windows, viewing ports of submersibles. It is extensively used to make signs, including lettering and logos, in medicine, it is used in bone cement and to replace eye lenses. Acrylic paint consists of PMMA particles suspended in water, acrylonitrile butadiene styrene is a terpolymer synthesized from styrene and acrylonitrile in the presence of polybutadiene. ABS is a material that exhibits high impact resistance and mechanical toughness. It poses few risks to health under normal handling. It is used in consumer products, such as toys, appliances. Nylon belongs to a class of polymers called polyamides and it has served as a substitute mainly for hemp, cotton and silk, in products such as parachutes, cords, sails, flak vests and womens clothing. Nylon fibers are useful in making fabrics, rope, carpets and musical strings, whereas in bulk form, Nylon is used for mechanical parts including machine screws, gears, in addition, it is used in the manufacture of heat-resistant composite materials. Polylactic acid is a biodegradable thermoplastic aliphatic polyester derived from renewable resources, such as starch, tapioca roots, chips or starch
9.
Synthetic rubber
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A synthetic rubber is any artificial elastomer. These are mainly polymers synthesised from petroleum byproducts, about 15 billion kilograms of rubbers are produced annually, and of that amount two thirds are synthetic. Global revenues generated with synthetic rubbers are likely to rise to approximately US$56 billion in 2020, synthetic rubber, like natural rubber, has uses in the automotive industry for tires, door and window profiles, hoses, belts, matting, and flooring. The expanded use of vehicles, and particularly motor vehicle tires, starting in the 1890s. In 1909, a team headed by Fritz Hofmann, working at the Bayer laboratory in Elberfeld, Germany, succeeded in polymerizing Isoprene, the first rubber polymer synthesized from butadiene was created in 1910 by the Russian scientist Sergei Vasiljevich Lebedev. This form of synthetic rubber provided the basis for the first large-scale commercial production by the tsarist empire and this early form of synthetic rubber was again replaced with natural rubber after the war ended, but investigations of synthetic rubber continued. Russian American Ivan Ostromislensky who moved to New York in 1922 did significant early research on synthetic rubber, political problems that resulted from great fluctuations in the cost of natural rubber led to the enactment of the Stevenson Act in 1921. By 1925 the price of rubber had increased to the point that many companies were exploring methods of producing synthetic rubber to compete with natural rubber. K. Neoprene is highly resistant to heat and chemicals such as oil and gasoline, the company Thiokol applied their name to a competing type of rubber based on ethylene dichloride which was commercially available in 1930. The first rubber plant in Europe SK-1 was established by Sergei Lebedev in Yaroslavl under Joseph Stalins First Five-Year Plan on July 7,1932, in 1935, German chemists synthesized the first of a series of synthetic rubbers known as Buna rubbers. These were copolymers, meaning the polymers were made up from two monomers in alternating sequence, other brands included Koroseal, which Waldo Semon developed in 1935, and Sovprene, which Russian researchers created in 1940. B. F. Goodrich Company scientist Waldo Semon developed a new, Ameripol made synthetic rubber production much more cost effective, helping to meet the United States needs during World War II. The production of rubber in the United States expanded greatly during World War II. Military trucks needed rubber for tires, and rubber was used in almost every other war machine, the U. S. government launched a major effort to improve synthetic rubber production. A large team of chemists from many institutions were involved, including Calvin Souther Fuller of Bell Labs, the rubber designated GRS, a copolymer of butadiene and styrene, was the basis for U. S. synthetic rubber production during World War II. By 1944, a total of 50 factories were manufacturing it and it still represents about half of total world production. The Ferrara, Italy, synthetic rubber factory was bombed August 23,1944, three other synthetic rubber facilities were at Ludwigshafen/Oppau, Hanover/Limmer, and Leverkusen. A synthetic rubber plant at Oświęcim in Nazi-occupied Poland, was construction on March 5,1944
10.
Styrene-butadiene
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Styrene-butadiene or styrene-butadiene rubber describe families of synthetic rubbers derived from styrene and butadiene. These materials have good resistance and good aging stability when protected by additives. In 2012, more than 5.4 million tonnes of SBR were processed worldwide, about 50% of car tires are made from various types of SBR. The styrene/butadiene ratio influences the properties of the polymer, with high styrene content, SBR is not to be confused with a thermoplastic elastomer made from the same monomers, styrene-butadiene block copolymer. SBR is derived from two monomers, styrene and butadiene, the mixture of these two monomers is polymerized by two processes, from solution or as an emulsion. E-SBR produced by polymerization is initiated by free radicals. Reaction vessels are typically charged with the two monomers, a free radical generator, and a transfer agent such as an alkyl mercaptan. Radical initiators include potassium persulfate and hydroperoxides in combination with ferrous salts, by capping the growing organic radicals, mercaptans, control the molecular weight, and hence the viscosity, of the product. Typically, polymerizations are allowed to proceed only to ca. 70%, in this way, various additives can be removed from the polymer. Solution-SBR is produced by a polymerization process. Polymerization is initiated by alkyl lithium compounds, the process is homogeneous, which provides greater control over the process, allowing tailoring of the polymer. The organolithium compound adds to one of the monomers, generating a carbanion that then adds to another monomer, relative to E-SBR, S-SBR is increasingly favored because it offers improved wet grip and rolling resistance, which translate to greater safety and better fuel economy, respectively. The material was initially marketed with the brand name Buna S and its name derives Bu for butadiene and Na for sodium, and S for styrene. It is a commodity material which competes with natural rubber, the elastomer is used widely in pneumatic tires. This application mainly calls for E-SBR, although S-SBR is growing in popularity, other uses include shoe heels and soles, gaskets, and even chewing gum. Latex SBR is extensively used in coated papers, being one of the cheapest resins to bind pigmented coatings and it is also used in building applications, as a sealing and binding agent behind renders as an alternative to PVA, but is more expensive. In the latter application, it offers better durability, reduced shrinkage and increased flexibility, SBR aids the bond strength, reduces the potential for shrinkage and adds an element of flexibility. It is also used by speaker driver manufacturers as the material for Low Damping Rubber Surrounds, additionally, it is used in some rubber cutting boards
11.
Allyl group
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An allyl group is a substituent with the structural formula H2C=CH−CH2R, where R is the rest of the molecule. It consists of a methylene bridge attached to a vinyl group, the name is derived from the Latin word for garlic, Allium sativum. In 1844, Theodor Wertheim isolated an allyl derivative from garlic oil, the term allyl applies to many compounds related to H2C=CH−CH2, some of which are of practical or of everyday importance, for example, allyl chloride. A site on the carbon atom is called the allylic position or allylic site. A group attached at this site is described as allylic. Thus, CH2=CHCH2OH has a hydroxyl group. Allylic C−H bonds are about 15% weaker than the C−H bonds in ordinary sp3 carbon centers and are more reactive. This heightened reactivity has many practical consequences, benzylic and allylic are related in terms of structure, bond strength, and reactivity. Other reactions that tend to occur with compounds are allylic oxidations, ene reactions. Benzylic groups are related to groups, both show enhanced reactivity. A CH2 group connected to two groups is said to be doubly allylic. The bond dissociation energy of C−H bonds on a doubly allylic centre is about 10% less than the bond energy of a C−H bond that is allylic. The weakened C−H bonds reflect the high stability of the resulting pentadienyl radicals, compounds containing the C=C−CH2−C=C linkages, e. g. linoleic acid derivatives, are prone to autoxidation, which can lead to polymerization or form semisolids. This reactivity pattern is fundamental to the behavior of the drying oils. The term homoallylic refers to the position on a skeleton next to an allylic position. In but-3-enyl chloride CH2=CHCH2CH2Cl, the chloride occupies a homoallylic position, the allyl group is widely encountered in organic chemistry. Allylic radicals, anions, and cations are often discussed as intermediates in reactions, all feature three contiguous sp²-hybridized carbon centers and all derive stability from resonance. Each species can be presented by two structures with the charge or unpaired electron distributed at both 1,3 positions
12.
Neoprene
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Neoprene or polychloroprene is a family of synthetic rubbers that are produced by polymerization of chloroprene. Neoprene exhibits good chemical stability and maintains flexibility over a temperature range. Neoprene is produced by polymerization of chloroprene. In commercial production, this polymer is prepared by free radical emulsion polymerization, polymerization is initiated using potassium persulfate. Bifunctional nucleophiles, metal oxides, and thioureas are used to crosslink individual polymer strands, outside of Russia and China, about 300,000 tons of neoprene are produced annually. After DuPont purchased the patent rights from the university, Wallace Carothers of DuPont took over development of Nieuwlands discovery in collaboration with Nieuwland himself. Arnold Collins at DuPont focused on monovinyl acetylene and allowed it to react with hydrogen chloride gas, DuPont first marketed the compound in 1931 under the trade name DuPrene, but its commercial possibilities were limited by the original manufacturing process, which left the product with a foul odor. A new process was developed, which eliminated the odor-causing byproducts and halved production costs, to prevent shoddy manufacturers from harming the products reputation, the trademark DuPrene was restricted to apply only to the material sold by DuPont. By 1939, sales of neoprene were generating profits over $300,000 for the company, Neoprene resists degradation more than natural or synthetic rubber. This relative inertness makes it suited for demanding applications such as gaskets, hoses. It can be used as a base for adhesives, noise isolation in power transformer installations and it resists burning better than exclusively hydrocarbon based rubbers, resulting in its appearance in weather stripping for fire doors and in combat related attire such as gloves and face masks. Because of its tolerance of extreme conditions, neoprene is used to line landfills, neoprenes burn point is around 260°C. Neoprene foam is used in many applications. Neoprene foam can be produced in either closed-cell or open-cell form, the closed-cell form is waterproof, less compressible and more expensive. The open-cell form can be breathable, Neoprene is used as a load bearing base, usually between two prefabricated reinforced concrete elements or steel plates as well to evenly guide force from one element to another. Neoprene is commonly used as a material for fly fishing waders, Neoprene waders are usually about 5 mm thick, and in the medium price range as compared to cheaper materials such as nylon and rubber. However, neoprene is less expensive than breathable fabrics, a foamed neoprene containing gas cells is used as an insulation material, most notably in wetsuits. Foamed neoprene is used in other insulation and shock-protection applications
13.
Reproductive toxicity
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Reproductive toxicity is a hazard associated with some chemical substances, that they will interfere in some way with normal reproduction, such substances are called reprotoxic. It includes adverse effects on function and fertility in adult males and females. It is usual to take a practical definition, including several different effects which are unrelated to each other except in their outcome of lowered effective fertility. One well known group of substances which are toxic for reproduction are teratogens – substances which cause birth defects – of which -thalidomide is possibly the most notorious, another group of substances which has received much attention as possibly toxic for reproduction are the so-called endocrine disruptors. Many drugs have effects on the reproductive system, these may be desired. However, most studies of reproductive toxicity has focussed on occupational or environmental exposure to chemicals and it may be noted that both consumption of alcohol and tobacco smoking are known to be toxic for reproduction in the sense that the term is used here. Bisphenol A is an example of an endocrine disruptor which negatively affects reproductive development, BPA is a known as estrogen mimicker and a likely androgen mimicker, which is used in the production of various plastic products. BPA exposure in female rats lead to mammary gland morphogenesis, increased formation of ovarian tumors. Additionally, BPA affects male fertility by resulting in lower sperm quality quality, the toxicological impact of BPA is better understood and studies in females than in males. Lead is a metal that not only has been associated with mental deficits. Lead is believed to affect male reproduction via disruption of hormones. Through this hormonal disruption, the process of production in the seminiferous tubules is reduced. Other reproductive toxins such as Thalidomide were once prescribed and used for therapeutic effects, in the 1950s and early 1960s, Thalidomide was widely used in Europe as an anti-nausea medication to alleviate morning sickness in pregnant women. It wasnt until the 1960s was found that Thalidomide altered embryo development and led to limb deformities such as thumb absence, under development of entire limbs, the teratogenic effects of Thalidomide have been proposed to affect more that ten thousand babies worldwide. Diethylstilbestrol, a synthetic estrogen known to be another reproductive toxin, was used from 1938 to 1971 to prevent spontaneous abortions from occurring in women, DES causes carcinogenic and mutagenic effects via the production of highly reactive metabolites, furthermore resulting in the formation of DNA adducts. Individuals exposed to DES in utero suffer atypical reproductive tract formation, specifically, females exposed, in utero, to DES during the first trimester have an increased risk of developing clear cell vaginal carcinoma, and males an increased risk of hypospadias
14.
Silicone rubber keypad
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Silicone rubber keypads are used extensively in both consumer and industrial electronic products as a low cost and reliable switching solution. The technology uses the compression molding properties of rubber to create angled webbing around a switch center. On depression of the switch the webbing uniformly deforms to produce a tactile response, when pressure is removed from the switch the webbing returns to its neutral position with positive feedback. In order to make an electronic switch a carbon or gold pill is placed on the base of the center which contacts onto a PCB when the web has been deformed. It is possible to vary the tactile response and travel of a key by changing the webbing design and/or the shore hardness of the base material. Unusual key shapes can easily be accommodated as can key travel up to 3mm, tactile forces can be as high as 500g depending on key size and shape. The snap ratio of a keypad determines the tactile feel experienced by the user, the recommended snap ratio for designers to maintain is 40%-60%, if dropped below 40% the keys will lose tactile feel but have an increased life. Loss of tactile feel means the user will not receive a ‘click’ feedback during actuation, snap ratio is calculated by taking the / ACTUATION FORCE. By adding pigments to the silicone rubber it is possible to create keys in various colors which can be molded together during the compression process to form a multi key keypad. Individual legends can be printed on to a key allowing full customization of the keypad for its application, techniques have also been developed to allow for keypads to be spray painted and legends then laser etched through the paint coating. This allows individual key to be illuminated using SMT LEDs placed on the circuit board. Also several coating materials such as Sealplast coating can be done to ensure a smooth surface where the printed legend last longer with good feeling of touch, laser etching is the laser controlled process of removing the top coat layer of a painted keypad to reveal lighter colored layer below. The effect is to produce an enhanced backlight effect by only lighting the legends on a keypad, by combining laser etching with either EL backlighting or LED backlighting in a range of color options it is possible to produce an interesting range of effects. Also the contact resistance can be customized based on electronics need where contact pills can be of different resistance, a general carbon pill can be of around 20 to 100 ohms, a low resistance contact pill can be up to 10 ohms. Gold AU pill or Supra Conductive Pill can be used to get as low as only up to 1 ohm, common applications of silicone rubber keypads include remote controls for TV, video and HIFI units, electronic toys and games, and industrial control equipment. Mobile phone handset manufacturers have, in recent years, been the main consumer of rubber keypads worldwide, with the availability of low resistance pills such as SC pills and Gold pills, short-stroke metal dome contacts application of keypad in automotive market has increased significantly
15.
Silicone
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They are typically heat-resistant and rubber-like, and are used in sealants, adhesives, lubricants, medicine, cooking utensils, and thermal and electrical insulation. Some common forms include silicone oil, silicone grease, silicone rubber, silicone resin, more precisely called polymerized siloxanes or polysiloxanes, silicones consist of an inorganic silicon-oxygen backbone chain with organic side groups attached to the silicon atoms. So, silicones are polymers constructed from inorganic-organic monomers, Silicones have in general the chemical formula n, where R is an organic group such as alkyl groups, or phenyl groups. In some cases, organic side groups can be used to two or more of these -Si-O- backbones together. By varying the -Si-O- chain lengths, side groups, and crosslinking, silicones can be synthesized with a variety of properties. They can vary in consistency from liquid to gel to rubber to hard plastic, the most common siloxane is linear polydimethylsiloxane, a silicone oil. The second largest group of materials is based on silicone resins. F. S. Kipping and Matt Saunders coined the word silicone in 1901 to describe polydiphenylsiloxane by analogy of its formula, Ph2SiO, with the formula of the ketone benzophenone, Ph2CO. Kipping was well aware that polydiphenylsiloxane is polymeric whereas benzophenone is monomeric and noted that Ph2SiO, Silicone is sometimes mistakenly referred to as silicon. The chemical element silicon is a crystalline metalloid widely used in computers, polysiloxanes are among the many substances commonly known as silicones. Molecules containing silicon-oxygen double bonds do exist and are called silanones, despite this, silanones are important as intermediates in gas-phase processes such as chemical vapor deposition in microelectronics production, and in the formation of ceramics by combustion. Most common are materials based on polydimethylsiloxane, which is derived by hydrolysis of dimethyldichlorosilane and this dichloride reacts with water as follows, n Si2Cl2 + n H2O → n + 2n HCl The polymerization typically produces linear chains capped with Si-Cl or Si-OH groups. Under different conditions the polymer is a cyclic, not a chain, for consumer applications such as caulks silyl acetates are used instead of silyl chlorides. The hydrolysis of the produce the less dangerous acetic acid as the reaction product of a much slower curing process. This chemistry is used in consumer applications, such as silicone caulk. Branches or cross-links in the chain can be introduced by using organosilicon precursors with fewer alkyl groups. Ideally, each molecule of such a compound becomes a branch point and this process can be used to produce hard silicone resins. Similarly, precursors with three groups can be used to limit molecular weight, since each such molecule has only one reactive site
16.
Shore durometer
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Durometer is one of several measures of the hardness of a material. Hardness may be defined as a resistance to permanent indentation. The durometer scale was defined by Albert Ferdinand Shore, who developed a device to measure Shore hardness in the 1920s, the term durometer is often used to refer to the measurement as well as the instrument itself. Durometer is typically used as a measure of hardness in polymers, elastomers, shores device was not the first hardness tester nor the first to be called a durometer, but today that name usually refers to Shore hardness. There are several scales of durometer, used for materials with different properties, the two most common scales, using slightly different measurement systems, are the ASTM D2240 type A and type D scales. The A scale is for softer plastics, while the D scale is for harder ones. However, the ASTM D2240-00 testing standard calls for a total of 12 scales, depending on the use, types A, B, C, D, DO, E, M, O, OO, OOO, OOO-S. Each scale results in a value between 0 and 100, with higher values indicating a harder material, durometer, like many other hardness tests, measures the depth of an indentation in the material created by a given force on a standardized presser foot. This depth is dependent on the hardness of the material, its properties, the shape of the presser foot. ASTM D2240 durometers allows for a measurement of the initial hardness, the basic test requires applying the force in a consistent manner, without shock, and measuring the hardness. If a timed hardness is desired, force is applied for the required time, the material under test should be a minimum of 6.4 mm thick. The ASTM D2240 standard recognizes twelve different durometer scales using combinations of specific spring forces and indentor configurations. These scales are properly referred to as types, i. e. a durometer type is specifically designed to determine a specific scale. The table below provides details for each of these types, with the exception of Type R. Note, Type R is a designation, rather than a true type. The R designation specifies a presser foot diameter of 18 ±0.5 mm in diameter, while the spring forces, the final value of the hardness depends on the depth of the indenter after it has been applied for 15 seconds on the material. If the indenter penetrates 2.54 mm or more into the material, if it does not penetrate at all, then the durometer is 100 for that scale. It is for this reason that multiple scales exist, durometer is a dimensionless quantity, and there is no simple relationship between a materials durometer in one scale, and its durometer in any other scale, or by any other hardness test. Using linear elastic indentation hardness, a relation between the ASTM D2240 hardness and the Youngs modulus for elastomers has been derived by Gentand by Mix and Giacomin
17.
International Standard Book Number
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The International Standard Book Number is a unique numeric commercial book identifier. An ISBN is assigned to each edition and variation of a book, for example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, the method of assigning an ISBN is nation-based and varies from country to country, often depending on how large the publishing industry is within a country. The initial ISBN configuration of recognition was generated in 1967 based upon the 9-digit Standard Book Numbering created in 1966, the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108. Occasionally, a book may appear without a printed ISBN if it is printed privately or the author does not follow the usual ISBN procedure, however, this can be rectified later. Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines, the ISBN configuration of recognition was generated in 1967 in the United Kingdom by David Whitaker and in 1968 in the US by Emery Koltay. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO2108, the United Kingdom continued to use the 9-digit SBN code until 1974. The ISO on-line facility only refers back to 1978, an SBN may be converted to an ISBN by prefixing the digit 0. For example, the edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has SBN340013818 -340 indicating the publisher,01381 their serial number. This can be converted to ISBN 0-340-01381-8, the check digit does not need to be re-calculated, since 1 January 2007, ISBNs have contained 13 digits, a format that is compatible with Bookland European Article Number EAN-13s. An ISBN is assigned to each edition and variation of a book, for example, an ebook, a paperback, and a hardcover edition of the same book would each have a different ISBN. The ISBN is 13 digits long if assigned on or after 1 January 2007, a 13-digit ISBN can be separated into its parts, and when this is done it is customary to separate the parts with hyphens or spaces. Separating the parts of a 10-digit ISBN is also done with either hyphens or spaces, figuring out how to correctly separate a given ISBN number is complicated, because most of the parts do not use a fixed number of digits. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency that is responsible for country or territory regardless of the publication language. Some ISBN registration agencies are based in national libraries or within ministries of culture, in other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded. In Canada, ISBNs are issued at no cost with the purpose of encouraging Canadian culture. In the United Kingdom, United States, and some countries, where the service is provided by non-government-funded organisations. Australia, ISBNs are issued by the library services agency Thorpe-Bowker
18.
Integrated Authority File
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The Integrated Authority File or GND is an international authority file for the organisation of personal names, subject headings and corporate bodies from catalogues. It is used mainly for documentation in libraries and increasingly also by archives, the GND is managed by the German National Library in cooperation with various regional library networks in German-speaking Europe and other partners. The GND falls under the Creative Commons Zero license, the GND specification provides a hierarchy of high-level entities and sub-classes, useful in library classification, and an approach to unambiguous identification of single elements. It also comprises an ontology intended for knowledge representation in the semantic web, available in the RDF format
19.
National Diet Library
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The National Diet Library is the only national library in Japan. It was established in 1948 for the purpose of assisting members of the National Diet of Japan in researching matters of public policy, the library is similar in purpose and scope to the United States Library of Congress. The National Diet Library consists of two facilities in Tokyo and Kyoto, and several other branch libraries throughout Japan. The Diets power in prewar Japan was limited, and its need for information was correspondingly small, the original Diet libraries never developed either the collections or the services which might have made them vital adjuncts of genuinely responsible legislative activity. Until Japans defeat, moreover, the executive had controlled all political documents, depriving the people and the Diet of access to vital information. The U. S. occupation forces under General Douglas MacArthur deemed reform of the Diet library system to be an important part of the democratization of Japan after its defeat in World War II. In 1946, each house of the Diet formed its own National Diet Library Standing Committee, hani Gorō, a Marxist historian who had been imprisoned during the war for thought crimes and had been elected to the House of Councillors after the war, spearheaded the reform efforts. Hani envisioned the new body as both a citadel of popular sovereignty, and the means of realizing a peaceful revolution, the National Diet Library opened in June 1948 in the present-day State Guest-House with an initial collection of 100,000 volumes. The first Librarian of the Diet Library was the politician Tokujirō Kanamori, the philosopher Masakazu Nakai served as the first Vice Librarian. In 1949, the NDL merged with the National Library and became the national library in Japan. At this time the collection gained a million volumes previously housed in the former National Library in Ueno. In 1961, the NDL opened at its present location in Nagatachō, in 1986, the NDLs Annex was completed to accommodate a combined total of 12 million books and periodicals. The Kansai-kan, which opened in October 2002 in the Kansai Science City, has a collection of 6 million items, in May 2002, the NDL opened a new branch, the International Library of Childrens Literature, in the former building of the Imperial Library in Ueno. This branch contains some 400,000 items of literature from around the world. Though the NDLs original mandate was to be a library for the National Diet. In the fiscal year ending March 2004, for example, the library reported more than 250,000 reference inquiries, in contrast, as Japans national library, the NDL collects copies of all publications published in Japan. The NDL has an extensive collection of some 30 million pages of documents relating to the Occupation of Japan after World War II. This collection include the documents prepared by General Headquarters and the Supreme Commander of the Allied Powers, the Far Eastern Commission, the NDL maintains a collection of some 530,000 books and booklets and 2 million microform titles relating to the sciences
