As an important thermoplastic resin, polypropylene (PP) is widely used in many fields. According to its polymerization mode and structural characteristics, it is mainly divided into homopolymer polypropylene (PP-H), block (impact-resistant) copolymer polypropylene (PP-B) and random (random) copolymer polypropylene (PP-R).
Homopolymer polypropylene (PP-H) is polymerized from a single propylene monomer. Its molecular chain has high regularity and high crystallinity, which makes it have good strength and excellent corrosion resistance. However, it also has some shortcomings, such as poor impact resistance and brittle texture; poor toughness and poor dimensional stability; it is also easy to age, has poor long-term heat resistance and stability, and may deform in high temperature environments. It is often used in the production of strapping, blow molding, brushes, ropes, woven bags and other products.
Block copolymer polypropylene (PP-B) is obtained by copolymerization of propylene and part of ethylene. Due to the presence of ethylene, it has better impact resistance and can withstand a certain degree of external force impact without being easily damaged. However, its low transparency and low gloss are obvious, and its moisture absorption resistance, acid and alkali corrosion resistance, solubility resistance and oxidation resistance at high temperature are relatively poor. It is often used in bumpers, thin-walled products, baby carriages, etc.
Random copolymer polypropylene (PP-R) is copolymerized by propylene monomer and a small amount of ethylene monomer. The random distribution of ethylene reduces the crystallinity and melting point of the polymer, bringing advantages of good comprehensive performance, such as high strength, high rigidity, good heat resistance, good dimensional stability, excellent low-temperature toughness, and good transparency and gloss. It is often used in products such as pipes, shrink films, and drip bottles.