Published on March 11, 2014
INTRODUCTION • A plastic material is any of a wide range of synthetic or semi- synthetic organic solids that are mouldable. • Plastics are typically organic polymers of high molecular mass, but they often contain other substances. • They are usually synthetic, most commonly derived from petrochemicals, but many are partially natural. • Synthetic resigns may be phenol, formaldehyde, cellulose vinyl, alkyl, etc. The moulding compounds are catalysts, fillers, hardeners, lubricants, pigments, plasticizers, solvents, etc.
• POLYMERIZATION: The simplest substances consisting of one primary chemical are known as the monomers or monoliths. They are to be combined or synthesized to form polymers by the process known as the polymerization. • POLYMER : The word polymer literally means “ many parts “. A polymeric solid material may be considered as to be one that contains many chemically bonded parts or units which themselves are bonded together to form a solid. • Two industrially important polymeric materials are: 1. Plastics 2. Elastomers • Plastics are a large and varied group of synthetic materials which are processed by forming or molding into shape. Just as we have many types of metals such as aluminium and copper, we have many types of plastics such as polyethylene and nylon.
• Plastics can be divided into two classes. 1. Thermo plastics 2. Thermo setting plastics, depending on how they are structurally and chemically bonded.
THERMO PLASTICS • Thermo plastics: These plastics can be softened by heating and hardened by cooling any number of times without changing the properties of the material. • It is thus possible to shape and reshape these plastics by means of heat and pressure. • One important advantage of this variety of plastics is that scrap obtained from old and warnout articles can be effectively used again. • Properties : 1. Softens and liquefies on heating and hardens up to cooling. 2. Retains shape after manufacture. 3. Suitable for recycling. 4. Can be reshaped by heat. 5. It may melt before passing to a gaseous state. 6. Allow plastic deformation when it is heated. 7. They are soluble in certain solvents. 8. Swell in the presence of certain solvents.
• Examples and applications of thermoplastic plastic materials: 1. High pressure polyethylene as applied to rigid material covered with electrical machines, tubes, etc... 2. Low pressure polyethylene elastic material used for insulation of electrical cables, etc... 3. Polystyrene applied for electrical insulation, handles of tools... 4. Polyamide used for making ropes, belts, etc... 5. PVC or polyvinyl chloride for the manufacture of insulation materials, pipes, containers, etc. • Examples of thermoplastic adhesives: 1. Acrylates 2. Cyanoacrylates 3. Epoxy cured by ultraviolet radiation 4. Acrylates cured by ultraviolet radiation
• THERMO PLASTIC MATERIALS : 1. Polyvinyl chloride ( P V C ) PROPERTIES : Rigid , tough , elastic to feel. Uses : Plumbing pipes and sanitary fittings are manufactured out of this material. Shower curtains , window frames, flooring , corrugated roofing sheets , plastic coating to steel sheets tanks, water cisterns, etc. 2. Acrylic : PROPERTIES: Glass clear , some what brittle sound when tapped. Uses : Glazing , bath rooms and sinks. PVC ACRYLIC
3. Polyethylene ( or polythene ) – low density: PROPERTIES: Flexible, feels like paraffin wax. Uses ; bottles, buckets, sheeting water tanks. 4. Polyethylene ( or polythene )- high density : PROPERTIES: stiff and hard, coarser than the polythylene of low density used as large storage bottles, water tank. 5. Polypropylene : PROPERTIES : smooth, rigid, lightest of all plastics – it floats in water. Uses : wc cisterns, sink traps, washing machine bids, food containers, appliances , car fender. POLYPROPYLENE POLYETHYLENE
6. Polystyrene : Solid ( glassy ) state at room temperature, but flows if heated above its glass transition temperature and becoming solid again when cooling off. Pure solid polystryrene is a colourless, hard plastic with limited flexibility. Polysterene can be transparent or can be made to take on various colours. Uses : Refrigerator containers , food trays, packaging, food containers, disposable cups, plates, cutlery, CD and cassette boxes. 7. Nylon : PROPERTIES : High density polythene but smoother to feel. Uses : Textiles , brush bristles, carpeting , surgical trays , bearings , pressure tubing. NYLON POLYSTYRENE
THERMOSETTING PLASTICS • These plastics are either originally soft or liquid or they soften once upon heating, they harden permanently. • When they are heated in the temperature of 127 degree centigrade to 177 degree centigrade , they set permanently and further application of heat does not alter their form of soften them. • But at temperature of about 343 degree centigrade, the charring occurs. The thermo setting plastics are durable, strong and hard. • They are available in a variety of beautiful colours. • They are mainly used in engineering applications of plastics.
• Properties : 1. Permanently hard on heating above a certain temperature. 2. Undergoes chemical changes during manufacture. 3. Cannot be melted and reshaped. 4. Little potential for recycling. • Examples and uses: 1. Polyester fibreglass systems: sheet molding compounds and bulk molding compounds) 2. Polyurethanes: insulating foams, mattresses, coatings, adhesives, car parts, print rollers, shoe soles, flooring, synthetic fibers, etc. Polyurethane polymers are formed by combining two bi- or higher functional monomers/oligomers. 3. Vulcanized rubber 4. Bakelite, a phenol-formaldehyde resin used in electrical insulators and plasticware 5. Urea-formaldehyde foam used in plywood, particleboard and medium-density fiberboard 6. Melamine resin used on worktop surfaces. 7. Epoxy resin used as the matrix component in many fiber reinforced plastics such as glass-reinforced plastic and graphite-reinforced plastic)
• THERMOSETTING PLASTIC MATERIALS 1. Melamine formaldehyde ( formica ): PROPERTIES : Hardest of common plastics , heat resistant. 2. Phenolics ( bakelite ) : PROPERTIES : The cheapest. Heavy solid plastic material, fishy smell when burnt dark in color. Heat resistant. Uses : Bottle caps, plastic automobile parts, bonding plywood and chip board, glues, laminates with other materials. FORMICA BAKELITE
3. Urea formaldehyde : PROPERTIES : Similar to phenolic but can be produced in lighter colours. Uses : Door furniture, light switches, and electrical fittings, glues, bottoms, radio cabinets, etc. 4. Epoxies: PROPERTIES: Resin and hardener. Uses: Used as adhesives. 5. Polyesters : PROPERTIES: produced as fibres and films. Uses ; Used for reinforced plastics. UF EPOXY
CLASSIFICATION ACCORDING TO STRUCTURE OF ATOMS According to this classification , the plastics are divided into 2 groups. • HOMOGENEOUS PLASTICS : This variety of plastic contains carbon chain ie, the plastics of this group are composed of carbon atoms only and they exhibit homogeneous structure. • HETEROGENEOUS PLASTICS : This variety of plastic is composed of the chain containing carbon and oxygen, the nitrogen and other elements and they exhibit heterogeneous structure.
Physical and mechanical properties • According to this classification, plastics are divided into four groups. 1. Rigid plastics 2. Semi –rigid plastics 3. Soft plastics 4. Elastomers. • RIGID PLASTICS : These plastics have high modulus of elasticity and they retain their shape under exterior stresses applied at normal or moderately increased temperatures. • SEMI- RIGID PLASTICS: These plastics have a medium modulus of elasticity and the elongation under pressure completely disappears, when pressure is removed. • SOFT PLASTICS: These plastics have a low modulus of elasticity and the elongation under disappears slowly, when pressure is removed. • ELASTOMERS : These plastics are soft and elastic materials with a low modulous of elasticity. They deform considerably under load at room temperature and return to their original shape, when the load is released. The extension can range up to ten times their original dimensions.
PROPERTIES OF PLASTICS The following properties are common with most of the plastics. 1.They are light in weight. 2. They have good resistance to most of the chemical. 3. They have high electrical strength. 4. They have good corrossive resistance. 5. Plastics can be moulded to any desired shape and size. 6. They can be made transperent or color. 7. They are cheap compared to metals. 8. All operations like drilling ,sawing, punching can be done on plastics. 9. Painting and polishing is not necessary. 10. The plastics posses excellent electric insulating properties. 11. The plastics, have low specific gravity, the average being 1.3 to 1.40.
PVC • Polyvinyl chloride, commonly abbreviated PVC, is the third-most widely produced plastic, after polyethylene and polypropylene. • PVC is used in construction because it is more effective than traditional materials such as copper, iron or wood in pipe and profile applications. • It can be made softer and more flexible by the addition of plasticizers, the most widely used being phthalates. • In this form, it is also used in clothing and upholstery, electrical cable insulation, inflatable products and many applications in which it replaces rubber.
• APPLICATIONS: PVC's relatively low cost, biological and chemical resistance and workability have resulted in it being used for a wide variety of applications. 1. It is used for sewerage pipes and other pipe applications where cost or vulnerability to corrosion limit the use of metal. 2. With the addition of impact modifiers and stabilizers, it has become a popular material for window and door frames. 3. By adding plasticizers, it can become flexible enough to be used in cabling applications as a wire insulator. 4. The material comes in a range of colors and finishes, including a photo- effect wood finish, and is used as a substitute for painted wood, mostly for window frames and sills when installing double glazing in new buildings, or to replace older single-glazed windows. 5. Other uses include fascia, and siding or weatherboarding. 6. This material has almost entirely replaced the use of cast iron for plumbing and drainage, being used for waste pipes, drainpipes, gutters and downspouts. 7. uPVC does not contain phthalates, since those are only added to flexible PVC, nor does it contain BPA. uPVC is known as having strong resistance against chemicals, sunlight, and oxidation from water.
ACRYLIC • In the plastics industry most acrylics are polymers of methyl methacrylate (PMMA). • Acrylics may be in the form of molding powders or casting syrups, and are noted for their exceptional clarity and optical properties. • Acrylics are widely used in lighting fixtures because they are slow-burning or even self-extinguishing, and they do not produce harmful smoke or gases in the presence of flame. • The most important properties for acrylic (PMMA) are its optical clarity, low UV sensitivity, and overall weather resistance. Acrylic is often used as a glass substitute.
• APPLICATIONS: 1. Transparent glass substitute. 2. Acrylic paint essentially consists of PMMA suspended in water; however since PMMA is hydrophobic, a substance with both hydrophobic and hydrophilic groups needs to be added to facilitate the suspension. 3. Laser cut acrylic panels have been used to redirect sunlight into a light pipe or tubular skylight and, from there, to spread it into a room. 4. panels have been commercialized for purposes of day lighting, to be used as a window or a canopy such that sunlight descending from the sky is directed to the ceiling or into the room rather than to the floor. This can lead to a higher illumination of the back part of a room, in particular when combined with a white ceiling, while having a slight impact on the view to the outside compared to normal glazing
POLYMER FILM • Plastic film/Polymer film is a thin continuous polymeric material. Thicker plastic material is often called a “sheet”. • These thin plastic membranes are used to separate areas or volumes, to hold items, to act as barriers, or as printable surfaces. • Plastic films are used in a wide variety of applications. • These include: packaging, plastic bags, labels, building construction, landscaping, electrical fabrication, photographic film, film stock for movies, video tape, etc.
FIBRE REINFORCED PLASTIC • Fibre-reinforced plastic (FRP) (also fibre-reinforced polymer) is a composite material made of a polymer matrix reinforced with fibres. • The fibres are usually glass, carbon, basalt or agamid, although other fibres such as paper or wood or asbestos have been sometimes used. • The polymer is usually an epoxy, vinylester or polyester thermosetting plastic, and phenol formaldehyde resins are still in use. • FRPs are commonly used in the aerospace, automotive, marine, and construction industries. • FRPs have been used widely in the design of new construction. Structures such as bridges and columns built completely out of FRP composites have demonstrated exceptional durability, and effective resistance to effects of environmental exposure.
• Pre-stressing tendons, reinforcing bars, grid reinforcement , and dowels are all examples of the many diverse applications of FRP in new structures. • One of the most common uses for FRP involves the repair and rehabilitation of damaged or deteriorating structures. • Several companies across the world are beginning to wrap damaged bridge piers to prevent collapse and steel-reinforced columns to improve the structural integrity and to prevent buckling of the reinforcement. • Architects have also discovered the many applications for which FRP can be used. These include structures such as siding/cladding, roofing, flooring and partitions.
SYNTHETIC RUBBER • Synthetic rubber, invariably a polymer, is any type of artificial elastomer mainly synthesised from petroleum byproducts. • Synthetic rubber, like natural rubber, has uses in the automotive industry for door and window profiles, hoses, belts, matting, flooring and dampeners (antivibration mounts). • Synthetic rubber displays the capacity of elasticity, synonymous in colloquial terms to bounciness, flexibility or pliability. • Water-repellent materials are those that do not allow water molecules to penetrate or pass through. Thus, synthetic rubber absorbs little to no water.
• Another property that makes it possible for synthetic rubber products to be used in the electrical industry is electrical resistance. • Synthetic rubbers exhibit high resistance to heat, meaning the material poorly conducts heat energy transference. • Certain synthetic rubbers display properties of chemical resistance, which in this instance means the chemical composition of the material cannot be readily changed through contact with other materials.
ASBESTOS CEMENT PRODUCTS • Asbestos Cement is primarily a cement-based product where about 10% to 15% w/w asbestos fibres are added to reinforce the cement. • Asbestos cement is weatherproof in that although it will absorb moisture, the water does not pass through the product. • It was used for corrugated sheets, slates, moulded fittings, soffits and undercloak, water cisterns, rainwater gutters, down pipes, pressure pipes, underground drainage and sewer pipes, sills, copings, chalkboards, fascias, infill panels, etc. • It is sometimes difficult to tell the difference between an asbestos cement product and a low-density insulation board. • Where the product has been used as a roofing or cladding product, open to the weather, you can be confident that the product is asbestos cement.
• ADVANTAGES OF PLASTICS OVER OTHER MATERIALS: 1. It can be moulded into finished products at a relatively low cost, compared to the machining and fabricating costs for wood and metal. 2. It resists chemicals. 3. It poses a high strength to weight ratio. 4. It does not rust like iron. 5. It is non conductor of electricity. 6. It is light in weight. 7. It is easy to fabricate. • DISADVANTAGE OF PLASTICS: 1. It has low modulus of elasticity. 2. It is not reliable with respect to weathering
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