Polyethylene (PE) is a thermoplastic that is one of the most commonly used materials in industry. Due to its excellent chemical resistance, mechanical properties and processing versatility, polyethylene is used in numerous water and wastewater treatment applications. This article explains the properties, manufacturing processes, specific applications and technical background of polyethylene in detail.

Chemical and physical properties of polyethylene

Polyethylene is a polymer that is produced by the polymerization of ethylene (C₂H₄). Depending on the polymerization process and material structure, PE is divided into different types that differ in their properties and applications.

1. structure and composition

• Molecular structure:
  • Polyethylene consists of long chains of CH₂ units that are connected by covalent bonds.
  • The chain arrangement determines the crystallinity and thus influences the mechanical and thermal properties.
• Variants of PE:
  • LDPE (low-density polyethylene):
    • Low density (0.91-0.93 g/cm³).
    • Highly branched structure, flexible, but lower strength.
  • HDPE (High-Density Polyethylene):
    • High density (0.94-0.97 g/cm³).
    • Linear structure, high rigidity and chemical resistance.
  • PE-RT (polyethylene for increased temperature resistance):
    • Modified form for use at higher temperatures.
  • PEX (cross-linked polyethylene):
    • Chemically or physically cross-linked molecular structure that leads to increased thermal stability and compressive strength.

2. mechanical and chemical properties

• Consistency:
  • Excellent resistance to chemicals, acids, alkalis and many solvents.
  • High UV and weather resistance with appropriate additives.
• Thermal properties:
  • Application temperature: -50 °C to approx. 80 °C (for HDPE, PE-RT up to 95 °C).
  • Low glass transition temperature, which means the material remains flexible at low temperatures.
• Mechanical properties:
  • High impact resistance, especially at low temperatures.
  • Flexibility (for LDPE) and high tensile strength (for HDPE).

Polyethylene production process

Polyethylene is produced by polymerizing ethylene using various catalysts and reactor technologies.

1. low pressure process (HDPE)

• Process: Polymerization of ethylene at low pressure (approx. 1-50 bar) and moderate temperatures (70-300 °C) using Ziegler-Natta or metallocene catalysts.
• Advantages: Control of chain length and structure, high density and strength.

2. high pressure process (LDPE)

• Process: Polymerization at high pressure (1,000-3,000 bar) and high temperatures (approx. 200-300 °C) in a tube or autoclave reactor.
• Advantages: Formation of branched chains that provide flexibility and transparency.

3. networking (PEX)

• Procedure:
  • Chemical cross-linking (e.g. by peroxides or silanes).
  • Physical cross-linking (e.g. through irradiation).
• Result: Increased compressive strength and thermal stability.