The difference between copolymer PP and homopolymer PP

Polypropylene (PP) is divided into homopolypropylene (PP-H), block (impact-resistant) copolymer polypropylene (PP-B) and random (optional) copolymer polypropylene (PP-R). What are the advantages, disadvantages and uses of PP? Let me share with you today.

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 cannot essentially solve the long-term heat resistance stability of PP-H performance.
Advantages: good strength.
Disadvantages: poor impact resistance (brittle), poor toughness, poor dimensional stability, easy aging, and poor long-term heat resistance stability.
Purpose: Extrusion blowing grade, flat yarn grade, injection molding grade, fiber grade, blown film grade. It can be used for packing belts, blowing bottles, brushes, ropes, woven bags, toys, folders, electrical appliances, household goods, microwave oven lunch boxes, storage boxes, wrapping paper films.
Discrimination method: When the fire is heated, the stretched wire is flat and not long.

2、Random copolymer polypropylene (PP-R)

It is obtained by copolymerization of propylene monomer and a small amount of ethylene (1-4%) monomer under heating, pressure and catalyst. The ethylene monomer is randomly and randomly distributed in the long chain of propylene. The random addition of ethylene reduces the crystallinity and melting point of the polymer, improves the impact of the material, long-term hydrostatic pressure resistance, long-term heat-resistant oxygen aging, and pipe processing and molding properties.
The 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 in polypropylene properties.
Advantages: good overall performance, high strength, high rigidity, good heat resistance, good dimensional stability, excellent low temperature toughness (good flexibility), good transparency, and good gloss.
Disadvantages: The best performance in PP.
Uses: film level, injection molding level. Tubes, shrink films, drip bottles, highly transparent containers, transparent household products, disposable syringes, packaging paper films.
Discrimination method: it will not turn black after being ignited, and can pull out a long round wire

3、Block (impact resistance) copolymer polypropylene (PP-B)

The ethylene content is relatively high, generally 7-15%, but because the probability that two ethylene monomers and three monomers are connected together in PP-B is very high, it shows that because the ethylene monomer only exists in the block phase, the The regularity of PP-H is reduced, so the purpose of improving PP-H’s melting point, long-term hydrostatic pressure resistance, long-term heat-resistant oxygen aging, and pipe processing and molding properties cannot be achieved.
Advantages: better impact resistance, a certain degree of rigidity improves the impact strength Disadvantages: low transparency, low gloss.
Disadvantages: moisture resistance, acid and alkali corrosion resistance, solubility resistance, poor oxidation resistance at high temperatures.
Uses: extrusion level, injection molding level. Bumpers, thin-walled products, strollers, sports equipment, luggage, paint buckets, battery boxes, thin-walled products
Discrimination method: it will not turn black after being ignited, and can pull out a long round wire
The flow rate MFR of PP is in the range of 1-40. PP materials with low MFR have better impact resistance but lower elongation strength. For materials with the same MFR, the strength of the copolymer type is higher than that of the homopolymer type. Due to crystallization, the shrinkage rate of PP is quite high, generally 1.8%-2.5%.

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