PP is polypropylene, also known as polypropene. It is a thermoplastic polymer used in a wide variety of applications including packaging and labeling, textiles (for example, ropes, thermal underwear and carpets), stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. It is an addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids.
PP is often opaque or colored using pigments. It is normally tough and flexible, reasonably economical, and has good resistance to fatigue. PP with higher MFR(melt flow rate) will fill the plastic mold more easily during the injection or blow-molding production process. But as the melt flow increases, some physical properties, like impact strength, will decrease. PP is recyclable and has the number “5” as its resin identification code.
There are three general types of polypropylene: homopolymer, random copolymer, and block copolymer. The comonomer is typically used with ethylene. Ethylene-propylene rubber or EPDM added to polypropylene homopolymer increases its low temperature impact strength. Randomly polymerized ethylene monomer added to polypropylene homopolymer decreases the polymer crystallinity, lowers the melting point and makes the polymer more transparent.