Polypropylene is the synthetic thermoplastic nonpolar polymer belonging to the class of polyolefines. It is a propylene polymerization product which represents the solid white colour substance. It is produced in the form of homopolymer and copolymer derived in the form of stabilized, coloured or colourless granules in the result of the copolymerization of propylene and ethylene over alkylmetal catalysts at low and medium pressures. The common designation of polypropylene in the Russian market is ПП but there are also other designations: PP (Polypropylene), PP HO or PP homopolymer (polypropylene homopolymer), HIPP (highly isotactic polypropylene homopolymer), PP-X, PP-XMOD (cross-linked polypropylene), PPCP or PP/Co or PP block-copolymer or PP impact copolymer (polypropylene block-copolymer, propylene and ethylene block-copolymer), PPМ (propylene and ethylene low-polyethylene block-copolymer), PPR (propylene and ethylene medium-polyethylene block-copolymer), PPU (propylene and ethylene high-polyethylene block-copolymer), PPH (propylene and ethylene very high-polyethylene block-copolymer), PP random copolymer (propylene and ethylene randomized copolymers), PP-EPDM or PP/EP (Polypropylene and ethylene, propylene and diene terpolymer mix), EPP (expandable polypropylene), EMPP (rubber-modified polypropylene), mРР (metallocene polypropylene).
The identification code of domestic polypropylene and propylene copolymers produced in accordance with GOST 26996-86 consists of the name of material – “Polypropylene” or “copolymer” and five digits. The first digit, 2 or 0, indicates that the process of polymerization proceeds over complex organo-metallic catalysts at low or medium pressure accordingly. The second digit designates the type of material: 1 – polypropylene; 2 – propylene copolymer. Three successive digits designate the ten-fold value of the melt flow index. Next to the dash the number of stabilization package is specified as well as the grade and the standard according to which polypropylene and its copolymers are produced.
An example of the identification code of polypropylene of grade 21020 stabilized according to stabilization package 02, 1st grade: Polypropylene 21020-02, 1st grade, GOST 26996-86. When producing coloured polypropylene or copolymer, a word specifying the colour and a three-digit number indicating the number of colouring formulation are added to the identification code.
An example of the identification code of polypropylene of grade 21030 stabilized according to stabilization package 06, 1st grade, coloured with red according to stabilization package 105: Polypropylene 21030-06, red, stab.pack. 105, 1st grade, GOST 26996-86.
Based on the identification code of polypropylene we can determine the melt flow index (MFI), having divided the last three-digit number in the grade of polypropylene by 10, and find the most suitable method of processing of a concrete grade of PP. MFI < 1 – extrusion; MFI from 2.5 to 4 – extrusion blowing, MFI 3 and more – injection moulding.
Polypropylene and propylene copolymers grades are determined depending on the method of their production, their properties and purpose.
In accordance with GOST 26996-86 low-pressure polypropylene includes eleven grades: 21003, 21007, 21012, 21015, 21020, 21030, 21060, 21100, 21130, 21180, 21230; medium-pressure polypropylene includes four grades: 01003, 01005, 01010, 01020; low-pressure polypropylene copolymers include three grades: 22007, 22015, 22030.
However there are also other polypropylene grades in the market as most manufacturers work according to own standard specifications.