Sustainable Food Packaging Barrier Coatings

Sustainable packaging is a hot topic.  Sustainable alternatives to conventional plastic packaging exist, and generally consist of biodegradable materials which are either derived from renewable natural sources, such as polysaccharides (e.g., starch, cellulose, chitosan, and alginate) or proteins (e.g., gelatin), or made from natural sugar derivatives (e.g. polylactic acid).
Despite many advantages, some of these materials do not meet certain standards required in food packaging, such as liquid and gas barrier properties.  Typically, barrier coatings are used to provide the required barrier properties.  However, the use of plastic-based materials as conventional barrier coatings can compromise the advantages of using a sustainable core material.  The same is true of plastic coatings on pulp-based materials such as carboard and paper, which can sometimes even prevent recycling.
It is therefore encouraging to read that new materials are emerging as sustainable barrier coatings for applications in packaging.  
Polyelectrolytes are macromolecules that contain a large number of charged functional groups. Polyelectrolyte complexes (PECs) can be formed spontaneously through blending oppositely charged polyelectrolytes where the ionic attraction is the major driving force.  Rather than relying on chemical irreversible crosslinking in conventional plastics, PECs are formed by reversible ionic associations without introducing crosslinkers, which can help meet needs of food and biomedical applications.  PECs fabricated with polysaccharides are termed polysaccharide polyelectrolyte complexes (PPCs).  
This article focuses on PPCs made from carboxymethyl cellulose (CMC) and chitosan (CS), which when applied to porous paperboard substrates paperboard using a particular manufacturing process, were found to exhibit outstanding barrier performance.