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 describes an unanticipated benefit of metallocene-catalyzed semicrystalline polyolefins, namely welded joint strengths in PE/iPP laminates that can exceed the cohesive strength of the constituents. We propose that interfacial polymer entanglements, established in the molten state and subsequently anchored in chain-folded lamellae upon crystallization, are responsible for this intrinsic property. The poor adhesion exhibited by traditional Ziegler-Natta-catalyzed polyolefins is shown to derive from the accumulation of amorphous polymer, a by-product of the polymerization reactions, at the interface. These results should facilitate fabrication and improve the properties of composites based on materials that dominate the plastics industry.
Chaffin
KA
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA. Exxon Chemical Company, Baytown Polymers Center, Baytown, TX 77522, USA.
Knutsen
JS
Brant
P
Bates
FS