Questions about PE

Polyethylene (PE) is the most produced type among general-purpose synthetic resins, including low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), as well as some products with special properties. LDPE is the abbreviation for high-pressure polyethylene, that is, low-density polyethylene. HDPE is the abbreviation for low-pressure polyethylene, that is, high-density polyethylene. The densities of these two types of polyethylene differ; HDPE generally has a density greater than 0.94, while LDPE has a density less than 0.925. Those with densities falling between these values are MDPE (medium-density polyethylene). Low-density polyethylene (LDPE) is usually produced by the high-pressure method (147.17–196.2 MPa), which is why it is also known as high-pressure polyethylene. Since the polyethylene produced by the high-pressure method has relatively many short and long side chains in its molecular chains (with an average of 21 side chains per 1000 carbon atoms), it has a lower degree of crystallinity (45%-65%), a lower density (0.910-0.925), is lightweight and flexible, and possesses good low-temperature resistance and impact resistance. LDPE is widely used in the production of films, flexible pipes, cable insulation and sheaths, synthetic leather, etc.

LDPE resin: Properties: tasteless, odorless, non-toxic; it has a matte surface and appears as milky-white waxy particles. Its density is approximately 0.920 g/cm3, with a melting point of 130°C to 145°C. Insoluble in water, slightly soluble in hydrocarbons, toluene, etc. It can resist the erosion of most acids and bases, has low water absorption, remains flexible at low temperatures, and possesses high electrical insulation properties. 　　Production process: There are mainly two methods, the high-pressure tubular method and the batch method. Based on the current development trends, in order to reduce the reaction temperature and pressure, the tubular process generally employs low-temperature, high-reactivity initiators to initiate the polymerization reaction. High-purity ethylene is used as the main raw material, while compounds such as propylene/propane are used as density regulators. The polymerization reaction is carried out using highly active initiators at temperatures of around 200°C to 330°C and pressures of 150–300 MPa. The molten polymer that initiates polymerization in the reactor must undergo cooling and separation at high pressure, medium pressure, and low pressure. The high-pressure cycle gas, after being cooled and separated, is sent to the inlet of the ultra-high pressure (300 MPa) compressor; the medium-pressure cycle gas, after cooling and separation, is sent to the inlet of the high-pressure (30 MPa) compressor; while the low-pressure cycle gas, after cooling and separation, is sent to the low-pressure (0.5 MPa) compressor for reuse. The molten polyethylene, after being separated at high and low pressures, is sent to a granulator where it is pelletized in water. During the granulation process, manufacturers can add appropriate additives depending on the intended application area, and the resulting pellets are then packaged and shipped out.