High-Strength Welds in Metallocene Polypropylene/Polyethylene Laminates
Kimberly A. Chaffin,
1*
Jeffrey S. Knutsen,
1
Patrick Brant,
2
Frank S. Bates
1
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.
1 Department of Chemical Engineering and Materials
Science, University of Minnesota, Minneapolis, MN 55455, USA.
2 Exxon Chemical Company, Baytown Polymers Center, Baytown,
TX 77522, USA.
*
Present address: Medtronic, Materials and Biosciences Center,
Brooklyn Center, MN 55430, USA.
To whom correspondence should be addressed. E-mail:
bates{at}cems.umn.edu
