Polyethylene is the most simple structure of the polymer, also the most widely used polymer materials.
It is made up of repeating units connected together CH2. Polyethylene is made by polymerizing ethylene(CH2=CH2).
The performance of polyethylene depends on its aggregation. Carried out under moderate pressure(15-30atm), under conditions of organic Ziegler-Natta catalyzed polymerization of high density polyethylene(HDPE). Under thease conditions the polyethylene polymerized molecule is linear, and the molecular chain is very long, the molecular weight of up to hundreds of thousands. If in a high pressure(100-300MPa), high temperature(190-210°C),under catalytic conditions peroxide radical polymerization, produce is low density polyethylene(LDPE), which is a branched structure.
Polymerization of pressure: high, medium, low;
Polymerization implementation methods: slurry, solution, gas phase
Product density size: high density, medium density, low density, linear low density.
Product weight: low molecular weight, molecular weight of ordinary, ultra high molecular weight.。（Provided by Shenzhen EPE）
Characteristics of Polyethylene
Polyethlen odorless, non-toxic, feel like wax, has excellent low temperature properities(lowest temperature up to -70 -- -100℃)，good chemical stability, resistance to most acid-base erosion(intolerance with oxidation properties acid), at room temperature, not soluble in common solvents, water absorption, excellent eletrical insulation properities; but polyethylene for environmental stress(chemical and mechanical action)is very sensitive, poor heat aging.
The nature of Polyethylene because of different varieties, depending on the molecular structure and density.
Types of polyethylene;
(1) LDPE：Low density polyethylene, high-pressure polyethylene
(2) LLDPE：Linear low density polyethylene
(3) MDPE：Medium density polyethylene, bimodal resins
(4) HDPE：High density polyethylene, low-pressure polyethylene
(5) UHMWPE：UHMWPE
(6)Modified polyethylene：CPE、XLPE(PEX)
(7)Ethylene copolymer：Ethylene - propylene copolymer (plastic))、EVA、Ethylene - butene copolymer、Ethylene - other olefins (such as octene POE, cyclic olefin) copolymers、Ethylene - unsaturated ester copolymer (EAA、 EMAA 、EEA、EMA、EMMA、EMAH)
The linear polyethylene of 3，000，000-6，000，000 a molecular weight called UHMWPE. The strength of UHMWPE is very high, it can be used to make bullet-proof vests.
Main method:
Liquid phase(also divided into solution method and slurry) and fumed(The material in the reactor of the type of phase). China mainly uses a Ziegler catalyst slurry.
Conditions and process description：More than 99% of ethylene in the catalyst of titanium tetrachloride and diethyl aluminum chloride presence, pressure and temperature 0.1-0.5MPa gasoline 65-75 ℃ in HDPE slurry polymerization. By alcoholysis destroy residual catalyst, and, washed, and recovered petrol and unpolymerized ethylene, dried, granulated product obtained
Chemical Name：Polyethylene
English Name: Polyethylene(简称PE)
Proportion:0.94-0.96 g/cm3 Molding shrinkage:1.5-3.6% Molding temperature：140-220℃
Features: corrosion resistance, electrical insulation (especially high-frequency insulation) fine, you can chlorination, chemical crosslinking, radiation crosslinking modified, can be glass fiber reinforced melting point, stiffness, hardness and strength than the low-pressure polyethylene. high water absorption, good electrical performance and radiation resistance; high-pressure polyethylene flexibility, elongation, impact strength and good permeability; ultra-high molecular weight polyethylene high impact strength, fatigue resistance, wear resistance. low-pressure polyethylene suitable for production of corrosion-resistant parts and insulating parts; high-pressure polyethylene film suitable for the production of the like; ultrahigh molecular weight polyethylene suitable for production of shock absorption, abrasion resistance and transmission parts.
Molding characteristics：
1.Crystalline material, moisture absorption is small, not be fully dry, excellent liquidity flow to pressure-sensitive, high-pressure injection molding is preferred, material temperature uniformity, fast filling, packing well. Not by direct gate to prevent uneven shrinkage , internal stress increases. Note that selection gate location and prevent shrinkage and deformation.
2.Shrinkage and shrinkage range of large, clear direction, easily deformed warping. Cooling rate should be slow, set the cold slug mold, and cooling system.
3.Heating time not too long, otherwise it will decompose.
4.When soft plastic parts have lighter side of the groove can be forcibly release.
5.It may melt fracture, not in contact with the organic solvent, to prevent cracking.
