Functional Properties
Barrier properties
Regarding the barrier properties of packaging materials, the critical compounds that can penetrate the packaging materials and degrade food quality are water vapor and oxygen of the surrounding atmosphere. To avoid the moisture transfer that can affect food quality, WVP control is important to assure stability and safety during distribution and storage. The ingress of oxygen, which is strongly and irreversibly reacted with food components such as lipids, vitamins, flavors, and colors, leads to permanent change in the nature of food products (rancidity, vitamin loss, and microbial contamination). Good oxygen barrier properties are critical for achieving a long shelf life for the packaged product. Other important gases to which food packaging should be less permeable are carbon dioxide and nitrogen.
To meet this demand, expensive synthetic barrier polymers, including EVOH copolymers and polyvinylidene chloride are commonly used in the form of laminates as oxygen-barrier layers in food packaging materials. Such composite synthetic laminates are not biodegradable and cannot be recycled. Therefore, there is an increasing interest in the development of biodegradable polymers for packaging materials that have suitable application properties and can be disposed of after use in an economically and ecologically acceptable way. The various potential functions of biopolymers used in paper coating are summarized in Table 1.
Biopolymers Functions Reference
WPI Increase printability of water-based ink Han and Krochta (1999)
Grease barrier Han and Krochta (2001)
Chan and Krochta (2001a)
NaCAS Oxygen barrier Khwaldia (2004)
NaCAS/paraffin wax bilayer Water vapor barrier Khwaldia (2009)
Corn zein Grease barrier Trezza and Vergano (1994)
Minimize effects of drying and brittleness
Corn zein/paraffin wax bilayer Water vapor barrier Parris and others (1998)
Grease barrier
SPI Gas and lipid barrier Park and others (2000)
SPI with CaCl2 posttreatment Water vapor barrier Rhim and others (2006)
WG Oxygen barrier Gällstedt and others (2005)
Carrageenan Grease barrier Rhim and others (1998)
HPMC/beeswax Water vapor barrier Sothornvit (2009)
Chitosan Fat barrier Ham-Pichavant and others (2005)
Gas barrier Kjellgren and others (2006)
Chitosan/sodium alginate bilayer Fat barrier Ham-Pichavant and others (2005)
Chitosan/carnauba wax bilayer Gas barrier Despond and others (2005)
Chitosan/sodium alginate bilayer Fat barrier Ham-Pichavant and others (2005)
Paraffin wax Water vapor barrier Parris and others (1998)
Table 1—. Functions of biopolymers used in paper coating.