High-strength welds in metallocene polypropylene/polyethylene laminates

Spectacular advances in organometallic chemistry over the past two decades have resulted in single-site catalysts that are revolutionizing Production of polyethylene (PE) and isotactic polypropylene (iPP). This report describ es an unanticipated benefit of metallocene-catalyzed semicrystalline polyol efins, namely welded joint strengths in PE/iPP laminates that can exceed th e cohesive strength of the constituents. We propose that interfacial polyme r entanglements, established in the molten state and subsequently anchored in chain-folded Lamellae upon crystallization, are responsible for this int rinsic property. The poor adhesion exhibited by traditional Ziegler-Natta-c atalyzed polyolefins is shown to derive from the accumulation of amorphous polymer, a by-product of the polymerization reactions, at the interface. Th ese results should facilitate fabrication and improve the properties of com posites based on materials that dominate the plastics industry.