NAMS 2002 Workshop - ICOM 2008

Packaging and Barrier Materials – 5
Friday July 18, 4:30 PM-5:00 PM, Wai’anae
Confined Crystallization of PEO in Nanolayered Films for Improved Gas
Barrier
H. Wang (Speaker), Case Western Reserve University, Cleveland, Ohio, USA
B. Freeman, The University of Texas at Austin, Austin, Texas, USA
A. Hiltner, Case Western Reserve University, Cleveland, Ohio, USA - pah6@case.edu
E. Baer, Case Western Reserve University, Cleveland, Ohio, USA
The goal of this project is to produce gas barrier materials for food packaging
with controlled atmosphere. Crystallization of polymer chains in a confined space
can generate unique morphologies and may impact the properties of the
polymeric material, such as the mechanical strength and gas barrier. Previously
confined polymer crystallization has been extensively studied in block
copolymers utilizing the nanoscale structure formed by their self-assembly. The
enabling technology of layer-multiplying coextrusion in the Center for Layered
Polymeric Systems (CLiPS) provides a unique opportunity to study the confined
crystallization of commercial polymers. In this study, assemblies of highly
crystalline poly (ethylene oxide) (PEO) layers with thickness ranging from 4
micron to 100nm were achieved by ‘forced assembly’ with ethylene-co-acrylic
acid copolymer (EAA). When the PEO layer thickness was in the micron scale (1-
4 micron), the PEO crystal orientation was isotropic and the gas barrier of PEO
layer was the same as the non- layered PEO. Upon further decreasing the PEO
layer thickness to around 100nm, atomic force microscopy and wide angle X-ray
diffraction showed that the long PEO lamellar crystals were aligned parallel to the
layer direction in these nanolayered films. The PEO/EAA nanolayered films
exhibited greatly improved gas barrier properties with the oxygen and carbon
dioxide permeability one order of magnitude lower than the microlayered films.
The improved barrier was attributed to the increased diffusion tortuosity in the
PEO layers because the long, impermeable PEO crystals were aligned
perpendicular to the gas diffusion direction. This observation reveals the potential
of making better barrier films from conventional polymeric materials.