Plastic Properties and technics (PE)
Polyethylene (PE) has the most simple structure of the polymer, but also is the most widely used polymer materials. PE is made from the repeated -CH2-unit connections. It is the addition polymerization of ethylene (CH2 = CH2). PE's performance depends on its aggregation.
High-density polyethylene (HDPE) is made by making Ziegler-Natta polymerization under moderate pressure (15-30 atm) and the organic compounds catalytic conditions.Polymerized under these conditions, polyethylene is linear, and the molecular chain is very long, the molecular is up to hundreds of thousands.
Free radical polymerization in a high pressure (10-300MPa) and high temperature (190-210℃), under the conditions of peroxide catalytic conditions, will produce Low-density polyethylene (LDPE), which is branched structure.
Polymerization pressure size: High, medium, low;
Polymerization implementation methods: Slurry Processing, solution method, gas method;
Product density size: high-density, medium density, low density, linear low density;
Product molecular: low molecular, normal molecular, high molecular.
Characteristics of Polyethylene: odorless, non-toxic, feel like wax, excellent low temperature resistance (the lowest temperature up to -70 ~ -100 ℃ ), good chemical stability, resist most of the acid-base erosion (intolerance oxidative nature of the acid), not soluble in common solvents at room temperature, low water absorption, excellent electrical insulation properties; but PE is sensitive to the environmental stress(chemical and mechanical action), and has poor heat and aging resistance.
The PE nature depends on different varieties. PE varieties:
1) LDPE: density polyethylene, high-pressure polyethylene.
2) LLDPE: linear low density polyethylene.
3) MDPE: medium-density polyethylene, bimodal resin.
4) HDPE: high density polyethylene, low-pressure polyethylene.
5) UHMWPE: ">ultra-high molecular polyethylene.
6) Modified polyethylene: CPE, cross-linked polyethylene (PEX).
7) Ethylene copolymer: ethylene propylene copolymer (plastic), EVA, ethylene butene copolymer, ethylene - other olefins (such as octene POE, cyclic olefin) copolymer, ethylene - unsaturated ester copolymer (EAA, EMAA, EEA, EMA, EMMA, EMAH), linear polyethylene whose molecular reached 3,000,000 - 6,000,000 is called ultra-high molecular polyethylene (UHMWPE). The strength of UHMWPE is very high, so which can be used to make body armor.
Physical properties of PE: transparent white waxy materials, soft and tough, lighter than water, non-toxic, has excellent dielectric properties, combustible and continues to burn when away from the fire, low permeability to water but high permeability to organic vapor. The transparence of PE decreased with the increase of crystalline in a certain degree of crystalline and increased with the increase of molecular weight. The range of Melting point of high-density polyethylene is 132-135℃, low-density polyethylene has low melting point (112℃) and a wide range. PE is not soluble in any known solvents in room temperature, but can be dissolved in a small amount in toluene, amyl acetate, three rates of ethylene, and other solvent when above 70℃.
The chemical properties of PE : excellent chemical stability, resistant to hydrochloric acid, hydrofluoric acid , phosphoric acid, formic acid, amine, sodium hydroxide, potassium hydroxide and other chemicals in room temperature, nitric acid and sulfuric acid have a stronger destruction to polyethylene.
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