Introducing the members of the polyethylene family! Do you know the difference between HDPE, LDPE, LLDPE, UHMWPE?
Introduction to Vinyl Plastics
Polyethylene (PE) is a thermoplastic resin obtained by polymerization of ethylene. And our commonly used polyethylene plastics are high molecular polymers made of polyethylene resin and various additives.
PE classification
According to the structural properties of polyethylene, it can be divided into:
1.High-density polyethylene (HDPE), also known as low-pressure polyethylene.
Preparation method:
Using high-purity ethylene as raw material, using Ziegler-Natta high-efficiency carrier titanium system as catalyst [catalyst composition: main catalyst TiCl4, carrier MgCl2, co-catalyst Al(C2H5)3], H2 as molecular weight regulator, in gasoline solvent Carry out coordination polymerization reaction to obtain HDPE with a density of 0.94～0.96g/cm³.
Structure and performance characteristics:
Its molecular weight is high, the branch chain is short, and the number is small, so the density is high. The tensile strength, tensile modulus, flexural modulus, hardness and other properties are better than LDPE, but the impact strength is worse than LDPE. The heat resistance is relatively high, the highest use temperature is 100℃, and the lowest use temperature is -70℃. The air permeability is 1/5 of LDPE. Especially suitable for packaging moisture-proof items.
2.Low-density polyethylene (LDPE), also known as high-pressure polyethylene, its molecular chain diagram is as follows:
Preparation method:
Using high-purity ethylene as raw material, under 150-300MPa pressure and 170-200℃, using oxygen, organic peroxides, and azo compounds as initiators for free radical polymerization, the obtained density is lower (0.91～ 0.93g/cm³), LDPE with a crystallinity of 55% to 65%.
Structure and performance characteristics:
There are a large number of branched structures, molecular structure lacks regularity, low crystallinity, heat resistance, solvent resistance, and poor hardness; but excellent electrical insulation, good flexibility, impact resistance and transparency are also Good; and has good air permeability.
3.Linear low density polyethylene (LLDPE), its molecular chain diagram is as follows:
Preparation method:
LLDPE is produced by low-pressure gas phase bulk method. In a fluidized bed reactor, chromium and titanium fluoride catalysts are attached to a silica gel carrier to form a catalytic system. H2 is used as a molecular weight regulator to copolymerize ethylene and a small amount of alpha olefins (pressure is 0.7～12.1MPa, temperature 85～95℃) to make LLDPE.
Structure and performance characteristics:
The molecular chain has a short branched structure, and the regularity of the molecular structure is between LDPE and HDPE, so the density and crystallinity are also between the two, closer to HDPE.
4.Ultra-high molecular weight polyethylene (UHMWPE)
Preparation method:
The same low-pressure polymerization method (Ziegler method) is used, without adding H2 to adjust the molecular weight, ultra-high molecular weight polyethylene (UHMWPE) can be synthesized, with a relative molecular weight of more than 1.5 million, a density of 0.92～0.94g/cm³, and crystallinity. It is 80%-85%.
Structure and performance characteristics:
Due to the large molecular weight, it has unique properties, such as excellent wear resistance, high impact strength, good self-lubrication, excellent low temperature resistance and chemical stability, and it is a low price. Plastics comparable to engineering plastics.
We can produce the HDPE plastic parts,the LDPE plastic parts,the LLDPE plastic parts,the UHMWPE plastic parts.
