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any organic material with the ability to flow into a desired shape when heat and pressure are applied to it and to retain the shape when they are withdrawn. Composition and Types of Plastic
..... Click the link for more information. noted for its light weight, being less dense than water; it is a polymerpolymer
, chemical compound with high molecular weight consisting of a number of structural units linked together by covalent bonds (see chemical bond). The simple molecules that may become structural units are themselves called monomers; two monomers combine to form a dimer,
..... Click the link for more information. of propylene. It resists moisture, oils, and solvents. Since its melting point is 121°C; (250°F;), it is used in the manufacture of objects that are sterilized in the course of their use. Polypropylene is also used to make textiles, ropes that float, packaging material, and luggage.
a thermoplastic polymer of propylene, [—CH2—CH(CH3)—]n; a colorlesscrystalline substance of iso-tactic structure. Molecular weight M̅w, 300,000–700,000; maximum crystallinity, 73–75 percent; density, 0.92–0.93 g/cm3 at 20°C; melting point, 172°C. Polypropylene has high impact strength (impact strength, notched 5–12 kilojoules per sq m, or kilograms-force · cm per sq cm), high resistance to multiple bending, and low vapor and gas permeability; its durability is comparable to that of the polyamides.
Polypropylene is a good dielectric (power factor, 0.0003–0.0005 at 1 megahertz) and a poor heat conductor. It is insoluble in organic solvents and resistant to boiling water and alkalies, but darkens and decomposes under the influence of HNO3, H2SO4, and chromium mixtures. Since polypropylene has low heat and light resistance, special additives called polymer stabilizers are introduced into the mixture.
Polypropylene is produced by solution or bulk polymerization of a monomer. It is processed by injection molding and extrusion. Polypropylene is used to manufacture fibers and films that retain their ductility at 100°-130°C, as well as expanded plastics, machine parts, shaped products, pipes (for aggressive liquids), various fittings, containers, and household goods.
The amorphous phase, in a 3–7 percent quantity formed during polypropylene synthesis, is isolated from the basic crystalline product and used in the manufacture of rubber household goods and additives for lubricating and motor oils. Polypropylene is produced in the USSR, Italy (Moplen), Great Britain (Propa-thene), the Federal Republic of Germany (Hostalen), and the USA (Poly-pro, Pro-fax). The 1973 world production of polypropylene was estimated at 2.4 million tons.
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