Polypropylene (PP) is a thermoplastic resin with the lowest density, which can be divided into homopolypropylene (pp-h) and copolymerized polypropylene. Copolymerized polypropylene is divided into block (impact resistant) copolymerized polypropylene (PP-B) and random (random) copolymerized polypropylene (PP-R). There are so many kinds of PP materials, what are the differences between them, Today, I'm here to learn about all kinds of PP.
1、PP-H
It is polymerized from a single propylene monomer. It is the lowest density of common plastics. Its molecular chain regularity is very high, so the material has high crystallinity and poor impact properties.
Advantages: good strength and corrosion resistance.
Disadvantages: poor impact resistance (relatively brittle), poor toughness, poor dimensional stability, easy aging, poor long-term heat stability, poor barrier to oxygen, carbon dioxide and other gases.
Usage: it can be used for packing belt, bottle blowing, brush, rope, woven bag, toy, folder, electrical appliances, household products, microwave oven lunch box, storage box, packaging paper film.
Discrimination method: when the fire burns, the silk is flat and not long.
2、PP-B
It is obtained by copolymerization of propylene and some ethylene, and the ethylene content is generally 7 ~ 15%. However, due to the very high probability of connecting two ethylene monomers and three monomers in PP-B, it shows that the ethylene monomer only exists in the block phase and does not reduce the regularity of pp-h, so it can not improve the melting point, long-term hydrostatic pressure resistance The purpose of long-term heat resistance and pipe processing and molding.
Advantages: good impact resistance.
Disadvantages: low transparency, low gloss, moisture absorption resistance, acid-base corrosion resistance, solubility resistance and poor oxidation resistance at high temperature.
Application: used for bumper, thin-walled products, stroller, sports equipment, luggage, paint bucket, battery box and thin-walled products.
Discrimination method: it does not blacken after ignition, and can pull out a long round wire.
3、PP-R
It is obtained by copolymerization of propylene monomer and a small amount of ethylene (1-4%) monomer under heating, pressure and catalyst. Ethylene monomer is 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 and oxygen aging and pipe processing and molding.
PP-R molecular chain structure and ethylene monomer content have a direct impact on the long-term thermal stability, mechanical properties and processability of the material. The more random the distribution of ethylene monomer in 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 and good gloss.
Disadvantages: PP has the best performance.
Usage: used for pipe, shrink film, drip bottle, high transparent container, transparent household products, disposable needle cylinder, packaging paper film.
Discrimination method: it does not blacken after ignition, and can pull out a long round wire.
4. Comparison of three kinds of polypropylene
Tensile yield strength: homopolypropylene > block co polypropylene > Random co polypropylene.
Rigidity: homopolypropylene > block copolypropylene > Random copolypropylene.
Impact strength: block co polypropylene > Random co polypropylene > homopolypropylene.
Transparency: random co polypropylene > homopolypropylene > block co polypropylene.
Low temperature toughness: block co polypropylene > Random co polypropylene > homopolypropylene.
