The most prominent property of polypropylene is its multi-faceted nature, which is suitable for many processing methods and uses. Its value and versatility are mainly derived from excellent chemical resistance, lowest density and highest melting point in bulk thermoplastics, and moderate cost. SHAOXING CLOTHO APPAREL CO.,LTD , https://www.clothoapparel.com
Chemistry and properties
Polypropylene (referred to as PP) differs from polyethylene (PE) in that the former has a methyl group every other carbon atom, which acts to harden the chain. Unless the methyl groups are on the same side of the chain, the polymer will not crystallize. Only soft and sticky atactic polypropylenes can be produced before Natta and Ziegler (independently) independently develop stereotactic catalysts. The hardness and resistance of commercial plastics are derived from crystallinity. The chain of PP is harder than PE, so PP has a higher melting temperature and tensile strength, but lower crystallinity. The PP homopolymer has a melting point of about 330 °F, depending on the heating rate and thermal history.
By intercalating ethylene (random copolymerization) on the PP chain, the chain becomes more irregular and softer, thereby reducing the crystallinity, modulus, melting point and melting point sharpness of the polymer. Typical random copolymers are relatively transparent and have a melting point in the range of 293-305 °F. As the ethylene content increases, the crystallinity of the polymer becomes lower and lower, eventually becoming ethylene-propylene rubber (EPR).
Another important class of copolymers are impact-resistant heterogeneous copolymers. These products are made by polymerizing rubber (sometimes PE) in a homopolymer matrix. The rubber used is typically EPR which produces a phase which is separated from the homopolymer matrix to form a haze. Translucent appearance. These materials are not true block copolymers because the rubber phase therein can be removed by solvent. A similar product can be obtained by blending EPR with PP, which has a melting point similar to that of a homopolymer.
Molecular weight and molecular weight distribution are important in PP processing. Melt flow at 446 T and 4.75 lb. load is an index of melt viscosity associated with weight average molecular weight. The melt flow of commercial polypropylene is as low as 0.25 g/10 min to as high as 800 g/10 min. The molecular weight distribution is expressed by the ratio of the weight average molecular weight to the number average molecular weight, and the ratio of the high crystallinity PP can be as high as 11; and the PP used as the meltblown fabric can be as low as 2. l. This ratio is extremely important in the fiber spinning process and affects extrusion, extrusion swell, molding internal stress and orientation processes.
Like most polymers, polypropylene oxidizes, especially during the melting process. In the case of PP, a radical that attacks the tertiary hydrogen is removed to protect the polymer. For long-term use of PP at high temperatures, complex multi-component stabilizer systems are used; for odor or taste limitations, the stabilization system must be very simple. If used for protection against sunlight (ultraviolet rays), carbon black can be added or a special stabilization method can be used.
Ordinary PP has a tensile strength of 34.5 MPa and a flexural modulus of about 1,723 MPa. There is a glass-filled grade PP with a tensile strength of 100 MPa and a flexural modulus of 9650 MPa. The mineral-filled grade PP can have a flexural modulus of up to about 4480 MPa, but the tensile strength does not increase much. The ductility is maintained at less than one 75 °F. Impact copolymers with tensile strengths as low as 18 6 MPa and flexural modulus as low as 689 MPa are not a recent variety. Modern polymerization processes produce materials that fill the gap between polypropylene and olefin rubber.
In addition to strong oxidizing agents and non-polar solvents, PP is highly resistant to chemical attack. For example, fuming nitric acid or hot concentrated sulfuric acid can degrade PP, but lower concentrations of solution are not harmful to PP. Liquids such as gasoline, xylene, and chlorinated hydrocarbons can swell and soften PP. The copolymer swells to a greater extent than the homopolymer. When PP is taken out of this type of solvent, its size will return to its original state. Due to the extreme inertness of the PP surface, it is difficult to print, paint and bond on PP without flame treatment or similar techniques.
Polypropylene has a high heat of combustion and it is difficult to produce flame retardant grade products, but there are several grades of flame retardant PP sold on the market. PP is also an excellent electrical insulator with a low dielectric constant and loss factor. It has good moisture resistance, but it is not a good oxygen barrier material.
use
Fiber is a major market for PP. By stretching or orienting, the tensile strength can be increased by as much as 15 times. The snagging products include clothing, diapers, and non-fabrics. Furniture leather, agricultural bags, ropes, floor coverings, belts. Carpet and carpet back village. The PP can also be cast or oriented to form a film. The oriented film can be used as a cigarette. Packaging materials for candy and many items; non-oriented film for capacitors or packaging materials.
PP sheets are used in thermoformed food containers, which must comply with FDA regulations in conjunction with moisture and gas transmission. The new very low modulus products can be calendered with a calender and compete with soft vinyl resins for the market.
The PP can be processed into a hollow product by an injection blow molding method, an extrusion blow molding method or a stretch blow molding method. In order to improve blow molding and thermoforming properties, high melt strength grade PP has been developed.
There is a fast processing extrusion grade PP on the market; the excellent electrical properties of polypropylene make it suitable for the insulation of telephone lines and data transmission cables.
Many different types of injection molded parts are made of PP or its impact copolymer. In the car market. Copolymers are used for internal assembly and panels, external components and batteries, etc.; homopolymer and fill grades are used for engine enclosures or instrument panels.
Glass filler grade PP is used as a component of an ornament or appliance. All unfilled PP resins can be used as writers, medical devices, including disposable radioactive sterilization products, mainly using low-cost homopolymers and random copolymers. Thin-wall molded containers expand the range of PP traditional packaging markets, such as tamper-proof sealers and dispensers.