Ther are two types of polyethylenes, low and hgh density. To produce low density polyethylene, ethylene is first obtained by refining the gas. It is then compressed, a peroxide is assed as a catalyst and chain modifier and hydrogen or carbon tetrachloride are also added. Polymerization occurs at elevated temperature, after which the polymer is extruded in ribbon form, cooled and granulated. High density polyethylene is obtained from gaseous ethylene fed into an inert hydrocarbon solvent with a catalyst.
Polymerization occurs at atmospheric pressure and at moderate temeperature.
The slurry output is then dried and the polymer separated. Limitation is that it has lower creep resistance and inferior fatigue properties compared to polypropylene. Resistant to a wide range of chemicals, most inorganic acids and alkalis at room temperature. Good moisture resistance. Insoluble in organic solvents below 60 C but may be swollen.