PP classification and properties advantages and disadvantages:
Polypropylene (PP) is divided into homo-polymer polypropylene (PP-H), block (impact) co-polymer polypropylene (PP-B) and random (random) co-polymer polypropylene (PP-R). What are the advantages, disadvantages and uses of PP? Share it with you today.
1. Homo-polymer polypropylene (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 the method of blending polyethylene and ethylene-propylene rubber to improve the toughness of the material, but it cannot fundamentally solve the long-term heat-resistant stability of PP-H. performance
Advantages: good strength
Disadvantages: poor impact resistance (more brittle), poor toughness, poor dimensional stability, easy aging, poor long-term heat resistance stability
Application: Extrusion blowing grade, flat yarn grade, injection molding grade, fiber grade, blown film grade. Can be used for strapping, blowing bottles, brushes, ropes, woven bags, toys, folders, electrical appliances, household items, microwave lunch boxes, storage boxes, wrapping paper films
Discrimination method: when the fire is burned, the wire is flat, and it is not long.
2. Random (random) copolymerized polypropylene (PP-R)
It is obtained by the co-polymerization of propylene monomer and a small amount of ethylene (1-4%) monomer under the action of heat, pressure and catalyst. The ethylene monomer is randomly and randomly distributed into the long chain of propylene. The random addition of ethylene reduces the crystallinity and melting point of the polymer, and improves the performance of the material in terms of impact, long-term hydrostatic pressure resistance, long-term thermal oxygen aging, and pipe processing and molding. 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 properties of the material. The more random the distribution of ethylene monomer in the propylene molecular chain, the more significant the change of polypropylene properties.
Advantages: good comprehensive performance, high strength, high rigidity, good heat resistance, good dimensional stability, excellent low temperature toughness (good flexibility), good transparency, good gloss
Disadvantages: the best performance in PP
Application: Extrusion blowing grade, film grade, injection molding grade. Tubes, shrink films, drip bottles, highly transparent containers, transparent household products, disposable syringes, wrapping paper films
Identification method: it does not turn black after ignition, and can pull out a long round wire
3. Block (impact) co-polymer polypropylene (PP-B)
The ethylene content is relatively high, generally 7-15%, but because the probability of connecting two ethylene monomers and three monomers in PP-B is very high, it shows that since the ethylene monomer only exists in the block phase, the The regularity of PP-H is reduced, so it cannot achieve the purpose of improving the performance of PP-H in terms of melting point, long-term hydrostatic pressure resistance, long-term thermal oxygen aging and pipe processing and forming.
Advantages: better impact resistance, a certain degree of rigidity improves impact strength
Disadvantages: low transparency, low gloss
Application: Extrusion grade, injection molding grade. Bumpers, thin-walled products, strollers, sports equipment, luggage, paint buckets, battery boxes, thin-walled products
Identification method: it does not turn black after ignition, and can pull out a long round wire
Common points: anti-hygroscopicity, acid and alkali corrosion resistance, solubility resistance, poor oxidation resistance at high temperature
The flow rate MFR of PP is in the range of 1-40. PP materials with low MFR have better impact resistance but lower ductility. For the same MFR material, the strength of the co-polymer type is higher than that of the homo-polymer type. Due to crystallization, the shrinkage of PP is quite high, generally 1.8-2.5%.
