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Imparting Barrier Properties in Flexible Packaging Applications

Posted on 1/18/2017 10:56:42 AM By Deb Bhattacharjee
  

Each layer in multilayer flexible packaging serves unique property for the benefit in its end use application, esp. for improving the shelf life of the packaged goods.  The packaging material needs to be versatile enough to withstand handling process forces maintaining physical integrity, resistance to chemicals, and suitable for barrier properties to several gases (e.g., O2, N2, CO2, moisture vapor).  The driver and trends of barrier materials for flexible packaging, including functionalities and global volumes of barrier materials like aluminum foil, PET film, nylon resins, metallized films, PVDC resin, EVOH resin, transparent oxide-coated film, COC (cyclic olefin copolymer) resin, AMAB (acrylonitrile-methyl acrylonitrile copolymer grafted with butadiene) resin, etc. are described in details in the recent article, “Barrier materials for flexible packaging”, Market Focus Research – 2011 to 2015, by Allied Development Corp.



What are the fundamental properties determining the difference in barrier properties?  


Barrier properties are correlated to the intrinsic structure of the polymer such as degree of crystallinity, crystalline/amorphous phase ratio, nature of polymer, orientation, thermal and mechanical treatment before and after food contact, polarity of chemical groups present into the polymer, degree of cross-linking, and glass transition temperature.  Furthermore, the intrinsic composition of the packed food (e.g., pH, fat content, aroma, etc.) would have an influence on the sorption characteristics of the packaging materials, while environmental factors like temperature and, for some polymers, relative humidity may affect their barrier characteristics.


The transport properties of the polymeric materials to small molecule permeants can be correlated with two polymer molecular structure parameters, that is, cohesive energy density (CED) and fractional free volume (FFV), determined by the group contribution method (International Journal of Polymer Science, P. Kubica and A. Wolinska-Grabczyk; May, 2015, Article ID 861979, 8 pages).

There are several comprehensive references illustrating transmission properties of oxygen, carbon dioxide and water vapor through a variety of polymeric film structure:

• “A twenty-year retrospective on plastics: oxygen barrier of packaging materials” by G. Strupinsky& A. Brody, TAPPI Publication 
• “Oxygen & water vapor barrier properties of flexible packaging films”, Du Pont Teijin Films, 2001
• “Oxygen transmission rate of a variety of films”, www.polyprint.com/flexographic-otr.htm
• “Permeability & Plastics packaging”, R. J. Ashley, Elsevier, p269-308, 1985
• “Permeability of polymeric packaging materials”, S. Zeman& L. Kubik, Technical Sciences, No. 10, 2007

Several allowed patents and patent applications disclose barrier coating compositions which comprise of treated (e.g. intercalation process allowing clay dispersion in polymer) and untreated nano-clay platelets in order to improve oxygen and moisture barrier properties while maintaining optical properties such as haze and gloss (e.g. US2009/0098395A1, US7078453, US7138452, US7119138, US6403231, US5334241) in thermoplastic films used in packaging applications. 


Excellent gas permeation resistance was claimed by applying a coating using the atomic layer deposition (ALD) method, which forms a thin (~25 nm), and even ceramic layer in between polymer layers acting like a glass (”New coating eliminates need for barrier films”, http://www.confectionerynews.com/Processing-Packaging, March 31, 2010)


While most of the barrier properties to oxygen would come from the plastic layers, design of the polymer backbone in adhesive could also play a very important part in improving the barrier properties.

While most of the barrier properties to oxygen would come from the plastic layers, design of the polymer backbone in adhesive could also play a very important part in improving the barrier properties.  This will be discussed in a later blog.