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  • General properties of thermosetting plastics are described in Art. 4.68. Following¬†are properties of several thermosetting plastics used in buildings:
    Phenol Formaldehyde. These materials provide the greatest variety of thermosetting molded plastic articles. They are used for chemical, decorative, electrical, mechanical, and thermal applications of all kinds. Hard and rigid, they change slightly, if at all, on aging indoors but, on outdoor exposure, lose their bright surface gloss. However, the outdoor-exposure characteristics of the more durable formulations are otherwise generally good. Phenol formaldehydes have good electrical properties, do not burn readily, and do not support combustion. They are strong, light in weight, and generally pleasant to the eye and touch, although light colors by and large are not obtainable because of the fairly dark-brown basic color of the resin. They have low water absorption and good resistance to attack by most commonly found chemicals.
    Epoxy and Polyester Casting Resins. These are used for a large variety of purposes.
    For example, electronic parts with delicate components are sometimes cast completely in these materials to give them complete and continuous support, and resistance to thermal and mechanical shock. Some varieties must be cured at elevated temperatures; others can be formulated to be cured at room temperatures.
    One of the outstanding attributes of the epoxies is their excellent adhesion to a variety of materials, including such metals as copper, brass, steel, and aluminum.

    Polyester Molding Materials. When compounded with fibers, particularly glass fibers, or with various mineral fillers, including clay, the polyesters can be formulated into putties or premixes that are easily compression- or transfer-molded into parts having high impact resistance. Polyesters are often used in geotextiles (Art. 6.11.2).
    Melamine Formaldehyde. These materials are unaffected by common organic solvents, greases, and oils, as well as most weak acids and alkalies. Their water absorption is low. They are insensitive to heat and are highly flame-resistant, depending on the filler. Electrical properties are particularly good, especially resistance to arcing. Unfilled materials are highly translucent and have unlimited color possibilities.
    Principal fillers are alpha cellulose for general-purpose compounding; minerals to improve electrical properties, particularly at elevated temperatures; chopped fabric to afford high shock resistance and flexural strength; and cellulose, mainly for electrical purposes.
    Cellulose Acetate Butyrate. The butyrate copolymer is inherently softer and more flexible than cellulose acetate and consequently requires less plasticizer to achieve a given degree of softness and flexibility. It is made in the form of clear transparent sheet and film, or in the form of molding powders, which can be molded by standard injection-molding procedures into a wide variety of applications. Like the other cellulosics, this material is inherently tough and has good impact resistance. It has infinite colorability, like the other cellulosics. Cellulose acetate butyrate tubing is used for such applications as irrigation and gas lines.
    Cellulose Nitrate. One of the toughest of the plastics, cellulose nitrate is widely used for tool handles and similar applications requiring high impact strength. The high flammability requires great caution, particularly in the form of film. Most commercial photographic film is cellulose nitrate as opposed to safety film.
    Polyurethane. This plastic is used in several ways in building. As thermal insulation, it is used in the form of foam, either prefoamed or foamed in place. The latter is particularly useful in irregular spaces. When blown with fluorocarbons, the foam has an exceptionally low K-factor and is, therefore, widely used in thin-walled refrigerators. Other uses include field-applied or baked-on clear or colored coatings and finishes for floors, walls, furniture, and casework generally. The rubbery form is employed for sprayed or troweled-on roofing, and for gaskets and calking compounds.
    Urea Formaldehyde. Like the melamines, these offer unlimited translucent to opaque color possibilities, light-fastness, good mechanical and electrical properties, and resistance to organic solvents as well as mild acids and alkalies. Although there is no swelling or change in appearance, the water absorption of urea formaldehyde is relatively high, and it is therefore not recommended for applications involving long exposure to water. Occasional exposure to water is without deleterious effect.
    Strength properties are good, although special shock-resistant grades are not made.
    Silicones. Unlike other plastics, silicones are based on silicon rather than carbon.
    As a consequence, their inertness and durability under a wide variety of conditions are outstanding. As compared with the phenolics, their mechanical properties are poor, and consequently glass fibers are added. Molding is more difficult than with  other thermosetting materials. Unlike most other resins, they may be used in continuous operations at 400F; they have very low water absorption; their dielectric properties are excellent over an extremely wide variety of chemical attack; and under outdoor conditions their durability is particularly outstanding. In liquid solutions, silicones are used to impart moisture resistance to masonry walls and to fabrics. They also form the basis for a variety of paints and other coatings capable of maintaining flexibility and inertness to attack at high temperatures in the presence of ultraviolet sunlight and ozone. Silicone rubbers maintain their flexibility at much lower temperatures than other rubbers.


  • Both thermosetting and thermoplastic molding materials are formed into final shape¬†by a variety of molding and fabricating methods.
    Thermosetting materials are commonly formed by placing molding powder or molded preform in heated dies and compressing under heat and pressure into the final infusible shape. Or they are formed by forcing heat-softened material into a heated die for final forming into the hard infusible shape.
    Thermoplastics are commonly formed by injection molding, that is, by forcing soft, hot plastic into a cold die, where it hardens by cooling. Continuous profiles of thermoplastic materials are made by extrusion. Thermoplastic sheets, especially transparent acrylics, are frequently formed into final shape by heating and then blowing to final form under compressed air or by drawing a partial vacuum against the softened sheet.
    Foamed plastics are employed for thermal insulation in refrigerators, buildings, and many other applications. In buildings, plastics are either prefoamed into slabs, blocks, or other appropriate shapes, or they are foamed in place.
    Prefoamed materials, such as polystyrene, are made by adding a blowing agent¬†and extruding the mixture under pressure and at elevated temperatures. As the¬†material emerges from the extruder, it expands into a large ‚Äė‚Äėlog‚Äô‚Äô that can be cut ¬†into desired shapes. The cells are ‚Äė‚Äėclosed‚Äô‚Äô; that is, they are not interconnecting¬†and are quite impermeable.

    Foamed-in-place plastics are made with pellets or liquids. The pellets, made, for example, of polystyrene, are poured into the space to be occupied, such as a mold, and heated, whereupon they expand and occupy the space. The resulting mass may be permeable between pellets. Liquid-based foams, exemplified by polyurethane, are made by mixing liquid ingredients and immediately casting the mixture into the space to be occupied. A quick reaction results in a foam that rises and hardens by a thermosetting reaction. When blown with fluorocarbon gases, such forms have exceptionally low thermal conductivities.
    All the plastics can be machined, if proper allowance is made for the properties of the materials.
    Plastics are often combined with sheet or mat stocks, such as paper, cotton muslin, glass fabric, glass filament mats, nylon fabric, and other fabrics, to provide laminated materials in which the properties of the combined plastic and sheet stock are quite different from the properties of either constituent by itself. Two principal varieties of laminates are commonly made: (1) High-pressure laminates employing condensation-type thermosetting materials, which are formed at elevated temperatures and pressures. (2) Reinforced plastics employing unsaturated polyesters and epoxides, from which no by-products are given off, and consequently, either low pressures or none at all may be required to form combinations of these materials with a variety of reinforcing agents, like glass fabric or mat.


  • Plastic is an organic material prepared out of resin. It may or may not contain fillers, plasticisers and¬†solvents. Plastic may be defined as a natural or synthetic organic material which are having the property¬†of being plastic at some stage of their manufacture when they can be moulded to required size and¬†shape.

    Shellac and bitumen are the natural resins used as plastic for a long time. In 1907, Blackland produced synthetic resin from the reaction of phenol and formaldehyde. The resin was hardened under pressure and heat to produce useful plastic articles.

    Types of Plastics

    Primarily there are two types of plastics:
    1. Thermosetting and
    2. Thermoplastic.
    1. Thermosetting Plastics: It needs momentary heated condition and great pressure during shaping. When heated cross linkage is established between the molecules and chemical reaction takes place. During this stage shape can be changed with pressure. This change is not reversible. The scrap of such plastic is not reusable. Bakelite is an example of such plastic.

    2. Thermoplastic: In this variety, the linkage between the molecules is very loose. They can be softened by heating repeatedly. This property helps for reuse of waste plastic. These plastic need time to cool down and harden. These plastics are to be kept in moulds till cooling takes place completely. Bitumen, cellulose and shellac are the examples of this variety of plastics.

    Properties of Plastics

    1. Colour: Some plastics are completely transparent. Using pigments plastics of any attractive
    colour can be produced.
    2. Dimensional Stability: It is dimensionally stable to a great extent.
    3. Durability: Plastic offers great resistance to moisture and chemicals and hence more durable.
    4. Electrical Insulation: The plastics possess excellent electrical insulating property.
    5. Fire Resistance: The phenol-formaldehyde and urea-formaldehyde plastics resist fire to a
    great extent and hence they are used as fire proofing materials.
    6. Strength: The plastics are reasonably strong. Their strength may be increased by reinforcing
    with various fibrous materials. Attempts are being made to produce structurally sound plastics.
    7. Specific Gravity: The specific gravity of plastics is very low and hence convenient to handle.
    8. Ductility: The plastics are not ductile and hence they fail without giving warning.
    9. Fixing: Plastics can be bolted, drilled, glued, clamped or simply push fitted in position.
    10. Maintenance: There is no maintenance cost for plastic articles i.e., they do not need painting and polishing.

    Uses of Plastics

    There are variety of plastics made to suit different uses. The typical uses of plastics in buildings is listed
    1. Corrugated and plain sheets for roofing.
    2. For making jointless flooring.
    3. Flooring tiles.
    4. Overhead water tanks.
    5. Bath and sink units.
    6. Cistern hall floats.
    7. Decorative laminates and mouldings.
    8. Window and door frames and shutters for bathroom doors.
    9. Lighting fixtures.
    10. Electrical conduits.
    11. Electrical insulators.
    12. Pipes to carry cold waters.



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