High-density polyethylene (HDPE) is a white powder or granular material. It is non‑toxic and odorless, with a crystallinity of 80%–90%, a softening point of 125–135°C, and a service temperature that can reach 100°C. Compared with low-density polyethylene, HDPE exhibits superior hardness, tensile strength, and creep resistance; it also offers good wear resistance, electrical insulation, toughness, and cold resistance. It demonstrates excellent chemical stability: at room temperature, it is insoluble in any organic solvent and resistant to corrosion by acids, alkalis, and various salts. Its films have low permeability to water vapor and air and exhibit minimal water absorption. However, HDPE has poor aging resistance and inferior resistance to environmental stress cracking compared with low-density polyethylene; thermal oxidation, in particular, can degrade its performance. Therefore, antioxidants and UV absorbers must be incorporated into the resin to mitigate these shortcomings. Additionally, HDPE films display a relatively low heat distortion temperature under load, so this should be taken into account during application.

Brief History of Development

This century has witnessed a revolutionary advancement in the pipeline sector: the substitution of steel with plastic. Driven by rapid breakthroughs in polymer science and technology, the deepening development and utilization of plastic pipe materials, and continuous improvements in manufacturing processes, plastic pipelines have fully demonstrated their outstanding performance. Today, plastic pipes are no longer mistakenly regarded as “low‑cost substitutes” for metal piping. In this transformative era, polyethylene pipes have gained widespread favor, shining ever more brightly, and are extensively employed in gas transmission, water supply, wastewater disposal, agricultural irrigation, the conveyance of fine solid particles in mining operations, as well as in oilfield, chemical, and telecommunications applications—particularly enjoying pervasive use in gas distribution.

HDPE is a thermoplastic polyolefin produced by the copolymerization of ethylene. Although HDPE was introduced as early as 1956, this material has yet to reach full maturity. This versatile polymer continues to be developed for new applications and markets.

In China, the major producers of high-density polyethylene (excluding HDPE produced at full-density polyethylene plants) are PetroChina, Sinopec, and CNOOC. As of the end of 2006, PetroChina operated four HDPE production units: the Lanzhou Petrochemical HDPE unit, the Daqing Petrochemical HDPE unit, the Liaoyang Petrochemical HDPE unit, and the Jilin Petrochemical HDPE unit.

High-density polyethylene is typically produced via Ziegler–Natta polymerization, characterized by the absence of side chains along the polymer backbone, resulting in a well‑ordered molecular structure and high density. This process involves the polymerization of ethylene in tubular or autoclave low-pressure reactors, with oxygen or organic peroxides serving as initiators.

High-density polyethylene is an environmentally friendly material that can be recycled and reused once it is heated to its melting point. It’s important to note that plastic resins are broadly classified into two main types: thermoplastics and thermosets. Thermosetting plastics, when heated to a certain temperature, undergo a chemical change that renders them permanently rigid; even further heating will not alter their state. Consequently, products posing environmental concerns are typically made from thermosetting plastics—such as tires—rather than thermoplastics—such as plastic pallets (note: in Hong Kong and Macau, pallets are referred to as “clamps”). Therefore, not all plastics are inherently non‑environmentally friendly.