High-density Polyethylene Features

The Features of High-density Polyethylene

High-density polyethylene has good heat and cold resistance, good chemical stability, high rigidity and toughness, and good mechanical strength. Dielectric properties, environmental stress cracking resistance is also good. Hardness, tensile strength and creep are superior to LDPE; The wear resistance, electrical insulation, toughness and cold resistance are good, but they are slightly worse than the low-density insulation; Good chemical stability, insoluble in any organic solvent under room temperature conditions, resistant to acid, alkali and various salts; The film has little permeability to water vapor and air and low water absorption; Poor aging resistance, environmental cracking resistance is not as good as low-density polyethylene, especially thermal oxidation will reduce its performance, so the resin needs to add antioxidants and ultraviolet absorbers to improve this deficiency. The heat deflection temperature of high-density polyethylene film is low under force, which should be paid attention to when applying [1].

Production process

The most common production method of PE is through slurry or gas phase processing, and a few are produced by solution phase processing. All of these processes are exothermic reactions involving ethylene monomers, a-olefin monomers, catalyst systems (which may be more than one compound), and various types of hydrocarbon diluents. Hydrogen and some catalysts are used to control molecular weight. The slurry reactor is generally a stirring kettle or a more commonly used large ring reactor, in which the slurry can be circulated. When ethylene and comonomers (as needed) come into contact with the catalyst, polyethylene particles are formed. After the diluent is removed, the polyethylene granules or powder granules are dried and additives are added in accordance with the dosage to produce the pellets. A modern line with a large reactor with a twin-screw extruder that can produce more than 40,000 pounds of PE per hour. The development of new catalysts contributes to the improvement of the performance of new grades of HDPE. The two most commonly used catalyst types are Philips' chromium oxide-based catalysts and titanium monoalkyl aluminum catalysts. The HDPE produced by Philip-type catalyst has a medium width molecular weight distribution; Titanium alkyl aluminum catalysts are produced with a narrow molecular weight distribution. Catalysts used to produce polymers with narrow MDW in complex reactors can also be used to produce wide MDW grades. For example, two tandem reactors producing significantly different molecular weights can produce a bimodal molecular weight polymer with a full wide molecular weight distribution.