How do low-density polyethylene and high-density polyethylene differ?

Low-density polyethylene (LDPE) and high-density polyethylene (HDPE) are both synthetic resins derived from the polymerization of ethylene, but they differ significantly in their molecular structure, manufacturing process, and physical properties.12

Structural and Manufacturing Differences

• Molecular Structure: LDPE features a polymer structure with both long and short branches, which prevent the chains from packing closely together. In contrast, HDPE has a linear structure with a lack of branches, allowing the chains to pack tightly.231
• Production: LDPE is prepared under very high pressures and temperatures using oxide initiators. HDPE is manufactured at low temperatures and pressures using Ziegler-Natta or metallocene catalysts, or activated chromium oxide.231

Physical Properties and Applications

• Characteristics: Due to its branched structure, LDPE is highly flexible and only partly crystalline, with a melting point of approximately 110 °C (230 °F). HDPE is a dense, highly crystalline material with high strength and moderate stiffness; its melting point is more than 20 °C (36 °F) higher than that of LDPE, allowing it to be sterilized.231
• Uses: LDPE is commonly used for packaging film, grocery bags, and squeeze bottles. HDPE is typically used for blow-molded bottles (such as milk jugs), pails, and appliance housings.231