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Polymeric Materials. By: Engr. Rizwan Nasir B.Sc. Chemical Engineering 13 October, 2009. Definition .
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Polymeric Materials By: Engr. Rizwan Nasir B.Sc. Chemical Engineering 13 October, 2009
Definition • A polymer (from Greek πολύ-ς /po΄li-s/ much, many and μέρος /΄meros/ part) is a large molecule (macromolecule) composed of repeating structural units typically connected by covalent chemical bonds. • While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a variety of properties. • A polymeric solid material may be considered to be one that contains many chemically bounded parts.
Plastic • The word plastic has many meanings. It is the class of material which can be molded or formed into many shapes. There are two types of plastic • Thermo setting • Thermoplastic
Thermoplastic • Thermoplastic requires heat to make formable and after cooling retain their shape. • These materials can be reheated and reformed into new shapes without sufficient change in its properties. • Thermoplastic consists of very long chains of C – atoms covalently bonded together. • Some time nitrogen, oxygen and sulphur atoms are also bounded in the main molecular chain.
Thermosetting plastics • Thermosetting plastics (thermo sets) are polymer materials that irreversibly cure. The treatment may be done through heat (generally above 200 degrees Celsius), through a chemical reaction (two-part epoxy, for example), or irradiation such as electron beam processing. • Permanently hardening or solidifying on being heated. Used of certain synthetic resins. • Most of the thermosetting plastics consist of a network of carbon atom covalently bonded together to form a rigid solid.
Properties & Uses of Plastic Properties They have wide range of properties: • It is low in cost. • It is good insulator. Uses The use of plastics for mechanical engineering design offer many advantages: • Simplified assembly • Weight saving • Noise reduction Plastics are very useful for many electrical engineering design because of their excellent insulative property: • Conductors • Switches • Computer components
Definition • In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains.
Types of polymerization There are four types of polymerization: • Bulk polymerization • Suspension polymerization • Solution polymerization • Emulsion polymerization
Bulk Polymerization • Bulk polymerization is carried out in the absence of any solvent or dispersant and is thus the simplest in terms of formulation. • It is used for most step-growth polymers and many types of chain-growth polymers. • In the case of chain-growth reactions, which are generally exothermic, the heat evolved may cause the reaction to become too vigorous and difficult to control unless efficient cooling...
Solution Polymerization • Solution polymerization is a method of industrial polymerization. In this procedure, a monomer is dissolved in a non-reactive solvent that contains a catalyst. The heat released by the reaction is absorbed by the solvent, and so the reaction rate is reduced. • This process is one of two used in the production of sodium polyacrylate, a super absorbent polymer used in disposable nappies (diapers).
Suspension Polymerization • The monomer is mixed with a catalyst and then dispersed as a suspension in water. • In this process the heat released by the reaction is absorbed by the water. • After polymerization, the polymerizes product is separated and dried. • This process is used to produce many of the vinyl type polymers such as PVC, polystyrene, polyacrylonitrile and polymethylmethacrylate
Emulsion polymerization • This polymerization process is similar to the suspension process since it is carried out in the water. • However emulsifier is added to disperse the monomer into very small particles. • An emulsifier is a type of surfactant typically used to keep emulsion (mixtures of immiscible fluids) well dispersed. Emulsifiers typically have a hydrophobic (water-hating) and a hydrophilic (water-liking) end. This action helps keeps the dispersed phase in small droplets and preserves the emulsion.
Polypropylene • Polypropylene is a thermoplastic polymer, synthesized from the low cast petrochemicals raw materials and used in a wide variety of applications, including food packaging, textiles, plastic parts and reusable containers of various types, thermal pants and shirts made for the military, laboratory equipment, loudspeakers, automotive components, and polymer banknotes.
Properties • It is good resistant to moisture • Chemical & heat resistant • 0.900 – 0.910 g/cm3 is its density • It is low cost polymers • Its melting point is 165 – 177oC
Polytetrafluoroethylene (PTEF) Teflon • R.J Planket in 1938 • In chemistry, polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene which finds numerous applications. • PTFE is most well known by the DuPont brand name Teflon.
Properties & Uses Properties: • PTFE is a crystalline polymers. • Its melting point is 327oC. • The density of PTFE is 2200 kg/m3 • It has an exceptional resistance to chemical & corrosion attack. • It is insoluble in all organic compounds. Uses: • It is used for chemical resistant pipes, pump parts, high temperature cable insulation, insulating tubes, packaging, gas kits, seals and bearings
Cont… The main disadvantages of PTFE: • Low melting point • Low thermal conductivity • Relatively low load carrying capacity (as compared to boron nitride, molybdenum disulfide and graphite) Because of the disadvantages Polytetrafluoroethylene is used in light low speed applications.
Polyvinylchloride (PVC) • PVC is a widely used synthetic plastic that has a 2nd largest sales in USA. • It has a unique ability to mix with additives.
Properties • PVC is cheap and easy to assemble. • In recent years, PVC has been replacing traditional building materials such as wood, concrete and clay in many areas. • It has relatively high strength. • It is highly solvent resistance & chemical resistance.
Uses There are many uses for PVC. • As a hard plastic, it is used as vinyl siding, magnetic stripe cards, window profiles, gramophone records (which is the source of the name for vinyl records), pipe, plumbing and conduit fixtures. • The material is often used in Plastic Pressure Pipe Systems for pipelines in the water and sewer industries because of its inexpensive nature and flexibility.
Uses • It can be used only few application without the addition of number of compounds. • The compounds which can be added to PVC to make it versatile are • Plasticizer • Heat stabilizer lubricants • Thinners • Pigments
Plasticizer: • They decrease the tensile strength of the PVC, e.g. phthalates, Diisooctyl phthalate (DIOP), all-purpose plasticizer for polyvinyl chloride, polyvinyl acetate, rubbers, cellulose plastics, and polyurethane Heat Stabilizers: • They are added to PVC to prevent thermal degradation during processing and help to extend the life of finished product. For example organo metallic compounds based on tin, lead, calcium and zinc.
Lubricants: • Lubricants aid the melt flow of PVC compounds during processing. Waxes, metallic soaps are used as lubricants. Fillers: • Fillers are mainly added to lower the cost of PVC. • Approximately 80% of all the filler used in PVC is calcium carbonate. Titanium dioxide is second at around 12%. The remaining few percent is taken up by other materials, including glass and talc.
Polyamides (Nylons) • A polyamide is a polymer containing monomers of amides joined by peptide bonds. • They can occur both naturally, examples being proteins, such as wool and silk, and can be made artificially through step-growth polymerization, examples being nylons, aramids, and sodium poly(aspartate).
Nylon • In nylon, the repeating units contain chains of carbon atoms. (That is different from Kevlar, where the repeating units contain benzene rings). There are various different types of nylon depending on the nature of those chains. Nylon-6,6 • Nylon-6,6 is made from two monomers each of which contain 6 carbon atoms - hence its name. • One of the monomers is a 6 carbon acid with a -COOH group at each end - hexanedioic acid.
Properties & Uses Properties • It is highly crystalline. • Its melting point is 250 – 266oC. Uses: • Nylon can be used as the matrix material in composite materials, with reinforcing fibres like glass or carbon fiber, and has a higher density than pure nylon. • Such thermoplastic composites (25% glass fibre) are frequently used in car components next to the engine, such as intake manifolds, where the good heat resistance of such materials makes them feasible competitors to metals.
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