Answer: Polyethylene (PE), one of the most widely used plastics, is produced through the polymerization of ethylene, a hydrocarbon derived from natural gas or petroleum. The process varies depending on the type of polyethylene—high-density (HDPE), low-density (LDPE), or linear low-density (LLDPE)—but follows a general framework.
First, ethylene is obtained via steam cracking, where hydrocarbons like ethane or naphtha are heated to 750–900°C, breaking them into smaller molecules, including ethylene gas. This gas is purified and compressed. Polymerization then occurs in one of two primary methods: high-pressure or low-pressure processes.
For LDPE, high-pressure polymerization (1,000–3,000 bar) at 200–300°C is used. Ethylene is injected into a reactor with initiators like organic peroxides, triggering a free-radical chain reaction that forms long, branched polymer chains, giving LDPE its flexibility. For HDPE and LLDPE, a low-pressure process (1–100 bar) at 70–150°C is employed, using catalysts like Ziegler-Natta or metallocene. Ethylene is polymerized in a reactor (e.g., gas-phase or slurry), forming linear chains for HDPE’s strength or controlled branching for LLDPE’s toughness.
After polymerization, the polyethylene is extruded, cooled, and pelletized into small granules. Additives such as UV stabilizers or antioxidants may be mixed in to enhance properties. These pellets are then used in applications like packaging, pipes, or such as those made by Plextrusions.
