Polypropylene is a polymer of propylene. Abbreviated as PP. Polypropylene is rich in raw materials, excellent in comprehensive performance, easy to process and form, and has low production cost, so it has a wide range of uses. Its disadvantages are poor low temperature toughness and high brittle fracture temperature (8 ° C). In recent years, modified products have been obtained by copolymerization and blending methods, and their low temperature resistance, impact resistance and aging resistance have been improved. Therefore, the use is expanding. Since the 20th century 50 In the era of Nata, G. found that the industrial production has developed very rapidly since the discovery of isotactic polypropylene.
The main chemical and physical properties of polypropylene have a weight average molecular weight of about 3 to 7105; light weight, density of about 0.91 g / cm 3; melting temperature of about 174 ° C; high strength, hardness, wear resistance and chemical resistance; Good performance, can be used at 120 ° C; its performance is not affected by environmental humidity. Its products are excellent in bending fatigue resistance, can withstand hundreds of thousands of bends without damage. Good processing performance, low shrinkage during processing.
Polypropylene is polymerized by using propylene monomer as the main component. Industrial production methods include solvent method, liquid phase bulk method, gas phase bulk method and solution method. However, the solvent method is generally used, followed by the bulk method.
Polypropylene can be divided into homopolymerization grade and copolymerization grade according to the monomer composition of the polymerization. The homopolymerization grade is polymerized from a single propylene monomer, so it has high crystallinity, high mechanical strength and heat resistance. Copolymer grade polypropylene is obtained by copolymerization of a small amount of ethylene monomer during polymerization. According to the copolymerization method, there are two kinds of block copolymer polypropylene and random copolymer. The copolymer grade polypropylene has high impact strength. The random co-polypropylene has good transparency in addition to high impact strength.
Compared with other general-purpose thermoplastics, polypropylene has the advantages of small specific gravity, good rigidity, high strength, flex resistance, heat resistance temperature higher than 100 ° C and good chemical resistance. 2. The impact is poor, easy to age, and the molding shrinkage rate is large.
Depending on the requirements and use of the product, polypropylene can be modified by blending, filling, reinforcing, adding auxiliaries, and copolymerization, blending, cross-linking, etc. For example, calcium carbonate, talc, minerals, etc. can be added to improve Hardness, heat resistance, dimensional stability; addition of glass fiber, asbestos fiber, mica, glass beads, etc. to improve tensile strength, improve low temperature impact resistance, creep resistance; add rubber, elastomer, and other flexible polymerization In order to improve the impact properties, transparency, adding various special additives can impart properties such as weather resistance, antistatic, flame retardancy, electrical conductivity, electroplatability, nucleation, copper resistance, etc.
Polypropylene can be produced by injection molding, extrusion molding, blow molding, thermoforming, rotational molding, plastic coating, foaming, etc. It is produced by various processing methods which have different requirements on the melting properties of polypropylene. Injection molding grade, extrusion grade, blow molding grade, coating grade, fiber grade, film grade, rotomolding grade, etc. to meet different processing requirements.
The use of polypropylene is quite extensive. Through injection molding, polypropylene can be made into various industrial parts, electrical appliances, building materials and daily necessities; pipe, sheet, profile, flat wire, fiber, rope; Blow molding method to produce various small containers and bottles; production of IPP film by using blown film method and flat film method, CPP film, stretching to obtain high strength, high transparency OPP film; using rotary molding method to produce large chemical storage tank, Containers, etc.