What are the advantages and disadvantages of PPH and PPR pipes
PP pipe special materials are divided into three generations: the first generation is modified by homopolymer polypropylene, called PP-H, the second generation is made by PP and PE block copolymerization process, called PP-B, and the third generation It is modified by random copolymer polypropylene, called PP-R. Its main difference is: the processing performance and environmental stress cracking resistance of these three materials are successively improved. PP-B has poor strength and better impact resistance, PP-H has better strength and poor impact resistance (brittle), and PP-R prevents this defect.
The strength of PP-B and PP-H pipes dropped significantly after one year, while PP-R pipes still maintained higher strength even after 50 years. Some special types of imported PP-B have similar performance to PP-R and are also excellent raw materials for pipes. PP-R is obtained by copolymerization of propylene monomer and a small amount of ethylene monomer under heating, pressure and catalyst. The ethylene monomer is randomly and randomly dispersed into the long chain of propylene.
The random participation of ethylene reduces the crystallinity and melting point of the polymer, improves the impact of materials, long-term hydrostatic pressure resistance, long-term heat-resistant oxygen aging, and pipe processing and molding properties.
The PP-R molecular chain structure and ethylene monomer content have a direct impact on the long-term thermal stability, mechanical properties and processing properties of the materials. The more random the dispersion of ethylene monomer in the propylene molecular chain, the more significant the modification of polypropylene properties. PP-H 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 crystallinity of the material is high and the impact performance is poor. In order to improve the brittleness of PP-H, some raw material suppliers also use polyethylene and ethylene-propylene rubber blending to improve the toughness of the material, but they cannot substantially deal with the long-term heat resistance stability of PP-H. performance.