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Polypropylene (PP) is divided into homopolymer polypropylene (PP-H), block (impact resistance) copolymer polypropylene (PP-B) and random (random) copolymer polypropylene (PP-R), so what are the advantages and disadvantages of various PP, what is the use.

1. three different polypropylenes are introduced

1.1. Homopolypropylene (PP-H)

It is polymerized from a single propylene monomer, and the molecular chain does not contain ethylene monomer, so the regularity of the molecular chain is very high, so the material has high crystallinity and poor impact performance. In order to improve the brittleness of PP-H, some raw material suppliers also use polyethylene and ethylene propylene rubber blending modification methods to improve the toughness of the material, but it can not essentially solve the long-term heat stability of the PP-H.

Advantages: better strength

Disadvantages: poor impact resistance (brittle), poor toughness, poor dimensional stability, easy aging, poor long-term heat stability.

Uses: blow-out grade, flat yarn grade, injection molding grade, fiber grade, blown film grade. It can be used for packing belt, bottle blowing, brush, rope, woven bag, toy, folder, electrical appliances, household goods, microwave lunch box, storage box, packaging paper film.

Identification method: when the fire burns, the wire is flat and does not last long.

1.2. Random (random) copolymer polypropylene (PP-R)

The ethylene monomer is randomly and randomly distributed into the long chain of propylene by copolymerization of propylene monomer and a small amount of ethylene monomer (1-4%) under heat, pressure and catalyst. The random addition of ethylene reduces the crystallinity and melting point of the polymer, improves the performance of the material in terms of impact, long-term hydrostatic pressure resistance, long-term thermal oxygen aging and pipe processing. PP-R molecular chain structure, ethylene monomer content and other indicators have a direct impact on the long-term thermal stability, mechanical properties and processing performance of the material. The more random the distribution of ethylene monomer in the propylene molecular chain, the more significant the change in polypropylene properties.

Advantages: good comprehensive performance, high strength, good heat resistance, good dimensional stability, excellent low temperature toughness (good flexibility), good transparency, good gloss.

Disadvantages: poor high temperature resistance and poor rigidity.

Uses: blow-out grade, film grade, injection molding grade. Pipe, shrink film, drip bottle, high transparent container, transparent household goods, disposable syringe, packaging paper film.

Distinguish the way: not black after ignition, can pull out a long round wire.

3. Block (impact) copolymer polypropylene (PP-B)

The ethylene content is high, generally 7-15%, but because the probability of two ethylene monomers and three monomers being linked together in the PP-B is very high, it shows that the ethylene monomer only exists in the block phase and does not reduce the regularity of the PP-H, thus failing to achieve the purpose of improving the performance of PP-H melting point, long-term hydrostatic pressure resistance, long-term heat and oxygen aging resistance and pipe processing.

Advantages: better impact resistance, a certain degree of rigidity and improve the impact strength.

Disadvantages: low transparency, low gloss.

Uses: Extrude level, injection molding level. Bumpers, thin-walled products, strollers, sports equipment, luggage, paint buckets, battery boxes, thin-walled products.

Distinguish the way: not black after ignition, can pull out a long round wire.

Common points and differences of different polypropylene in 2.

2.1. Polypropylene, which is a thermoplastic resin obtained by polymerizing propylene. According to the arrangement position of methyl group, it is divided:

Isotactic polypropylene (isotactic polypropylene)

atactic polypropylene (atactic polypropylene)

　　间规聚丙烯(syndiotactic polypropylene)

Methyl groups arranged on the same side of the molecular main chain are called isotactic polypropylene. If methyl groups are arranged in disorderly order on both sides of the molecular main chain, they are called atactic polypropylene. When methyl groups are arranged alternately on both sides of the molecular main chain, they are called syndiotactic polypropylene. In the general industrial production of polypropylene resin, the isotactic structure content is about 95%, and the rest is atactic or syndiotactic polypropylene. Industrial products are mainly composed of isotactic substances. Polypropylene also includes copolymers of propylene with minor amounts of ethylene. Usually translucent colorless solid, odorless non-toxic.

Hint: Be careful not to confuse it here. The random polypropylene we often say should actually refer to 1.2. propylene-ethylene random (random) copolymer, English abbreviation: PP-R, while the random polypropylene here is distinguished by the arrangement of methyl groups, English abbreviation: APP.

Due to the regular structure and high degree of crystallization, the melting point of homo PP can usually be as high as 167 ℃.

Heat resistance, corrosion resistance, products available steam sterilization is its outstanding advantages. Low density, is the lightest general-purpose plastic. The disadvantages are poor low temperature impact resistance and poor oxidation resistance at high temperature, but they can be overcome by modification. Other advantages such as: anti-moisture absorption, anti-acid and alkali corrosion, anti-solubility, dielectric and electrical insulation. Due to crystallization, the shrinkage of PP is quite high, generally 1.5-2.5%.

2.2. Generally, the flow rate MFR of PP ranges from 1 to 40, while the average MFR is about 100, which is relatively good in China compared with Yanshan Petrochemical. Low MFR PP material has better impact resistance but lower tensile strength. For materials of the same MFR, the strength of the copolymer type is higher than that of the homopolymer type. Also add nucleating agent, PP-R can be more transparent than PP-H, PP-H more resistant to high temperature than PP-B.

Read the above introduction, we do thermoplastic elastomer modified material friends, will choose the right polypropylene? Usually the pursuit of mechanical properties is better, then choose random copolymer polypropylene, such as the pursuit of high temperature compression deformation, then choose homopolypropylene.