What are the key differences between HDPE, LDPE, and LLDPE in terms of production and applications?

What are the key differences between HDPE, LDPE, and LLDPE in terms of production and applications?
Polyethylene grades differ fundamentally by molecular structure. HDPE features linear chains with minimal branching, giving higher density (0.92-0.97 g/cm³), better heat resistance, mechanical strength, and chemical resistance—ideal for pipes, sheets, and containers. LDPE has long branches that prevent tight packing, making it softer and more flexible, suitable for films and bags. LLDPE, despite short branches, has lower density and is increasingly favored for packaging. Production routes vary: HDPE uses Ziegler-Natta catalysts in low-pressure processes (solution, slurry, or gas phase), while LDPE requires high-pressure free-radical polymerization at 100-300 MPa. Key licensors include Basell (Hostalen slurry), Chevron Phillips (MarTech loop slurry), and Univation (Unipol gas phase), each with distinct monomer preferences—butene for Basell versus hexene for Chevron Phillips.