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.
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
4.
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
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
