Three major classifications and performance comparisons of polypropylene (PP)

Polypropylene (PP) is the thermoplastic resin with the smallest density. It can be divided into homopolypropylene (PP-H) and copolymerized polypropylene. Copolymerized polypropylene is further divided into block (impact-resistant) copolymerized polypropylene (PP-H). B) and random (random) copolymerized polypropylene (PP-R). There are so many kinds of PP materials, so what are their differences? Today we will learn about various PPs with you.

PP-H

Polymerized from a single propylene monomer, it is the smallest density among common plastics. Its molecular chain is very regular, so the material has high crystallinity and poor impact properties.

Advantages: better strength and better corrosion resistance.

Disadvantages: poor impact resistance (brittle), poor toughness, poor dimensional stability, easy aging, poor long-term heat resistance and stability, and poor barrier properties to oxygen, carbon dioxide and other gases.

Usage: Can be used for packing tapes, blown bottles, brushes, ropes, woven bags, toys, folders, electrical appliances, household products, microwave lunch boxes, storage boxes, and wrapping paper films.

How to identify: When burned by fire, the wire will be flat and not long.

PP-B

It is obtained by copolymerizing propylene and part of ethylene. The ethylene content is generally 7 to 15%. However, because the probability of two ethylene monomers and three monomers being connected together in PP-B is very high, it means that the ethylene monomer only has embedded In the segment phase, the regularity of PP-H is not reduced, so the purpose of improving the melting point, long-term hydrostatic pressure resistance, long-term heat resistance and pipe processing and forming properties of PP-H cannot be achieved.

Advantages: better impact resistance.

Disadvantages: low transparency, low gloss, poor resistance to moisture absorption, acid and alkali corrosion resistance, solubility resistance and oxidation resistance at high temperatures.

Usage: Used in bumpers, thin-walled products, strollers, sports equipment, luggage, paint buckets, battery boxes, and thin-walled products.

How to identify: It does not turn black after being ignited and can pull out very long round wire.

PP-R

It is obtained by copolymerizing 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, improves the material's impact, long-term resistance to hydrostatic pressure, long-term resistance to 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 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 will be.

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: Best performance among PP.

Usage: Used in pipes, shrink films, drip bottles, highly transparent containers, transparent household products, disposable syringes, and packaging paper films.

How to identify: It does not turn black after being ignited and can pull out very long round wire.

Comparison of three types of polypropylene

Tensile yield strength: homopolypropylene>block copolymerized propylene>random copolymerized propylene

Rigidity: Homopolypropylene > Block copolymerized propylene > Random copolymerized propylene

Impact strength: block copolymerized propylene > random copolymerized propylene > homopolymerized propylene

Transparency: Random copolymerized propylene＞Homopolymerized propylene＞Block copolymerized propylene

Low temperature toughness: block copolymerized propylene > random copolymerized propylene > homopolymerized propylene