Encyclopaedic reference

Polypropylene,
thermoplastic polymer of propylene, [-CH2-CH (CH3)-] n; colourless crystalline substance of isotactic structure, molecular weight 300-700 thousands, maximum crystallinity degree is 73-75%, density 0,92-0,93 gr/cm3 at 20 °Ñ, tmelting 172 °Ñ. High shock strength is characteristic for polypropylene (impact strength with notch is 5-12 kilojoules/m2, orkilogram-force ×cm/cm2), high resistance to multiple bending, low vapor permeabilty and gas permeability; its wear resistance is comparable with the polyamide’s one. Polypropylene is a good dielectric (tangent of the dielectric losses angle is 0,0003- 0,0005 at 1 MHz), conducts heat badly. It is not dissolved in organic solvents, it is resistant to the action of boiling water and alkalis, but it gets dark and collapses under the influence of HNO3, H2SO4, chrome mixture. Polypropylene has low thermo - and light resistance, so special additives are introduced in it, such as stabilizers of polymeric materials

Polypropylene is obtained by the polymerization of the monomer in solution or mass then it is processed by pressure casting and extrusion. Fibers and films are manufactured from polypropylene, maintaining its flexibility in 100-130 °Ñ, foamed plastics, parts of machines, profiled products, pipes (for aggressive liquids), and various valves, containers, household articles, etc.

The amorphous phase formed in the synthesis of polypropylene in the quantity of 3-7% is separated from the main crystalline product and is used in the manufacture of household rubber products and additives for lubricating and motor oils.




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