Effects of plasticizing and crosslinking on coatings based on blends of starch-PVOH and starch-lignin

A barrier material is usually needed on a fiber-based food package to protect the packed food from gases and moisture and thus maintain its quality. Barrier materials presently used in food packaging applications are mostly petroleum-based polymers. Over the last few decades, efforts have been made to replace petroleum-based materials with bio-based materials. The present work has focused on the possibility of using a natural barrier material on a fiber-based food package and the effects of plasticizing and cross-linking on the mechanical and barrier properties, and the stability in water of coatings based on starch-poly(vinyl alcohol) (PVOH) and starch-lignin blends. The flexibility of the starch films was increased by adding PVOH further by adding a plasticizer. It was shown that citric acid can act as a compatibilizer and cross-linker for starch and PVOH, and the use of citric acid may slow down the diffusion of both oxygen and water vapor if a multilayer coating strategy is used. The addition of polyethylene glycol to the pre-coating recipe resulted in a lower oxygen transmission rate through polyethylene-extruded board than when citric acid was added to the pre-coating. The flexibility of the barrier coatings and the properties of the base substrate affect the cracking tendency of the barrier coatings during the creasing and folding of a barrier-coated board. The addition of lignin to the starch reduced the migration of starch from the starch-lignin films and the addition of ammonium zirconium carbonate as a cross-linker reduced the migration of both starch and lignin from the films. The addition of starch to the lignin solution increased the solubility of lignin at low pH, and the pilot-coated board showed a significant decrease in migration of lignin from the coatings containing ammonium zirconium carbonate when the pH of the coating solution was decreased.A barrier material is usually needed on a fiber-based food package to maintain quality by protecting packed food from gases and moisture. Over the last few decades, efforts have been made to replace petroleum-based materials with bio-based materials. The present work has focused on the possibility of using a natural barrier material on fiber-based food packaging materials, and the effects of plasticizing and cross-linking on the mechanical and barrier properties and on the stability in water of coatings based on starch-PVOH and starch-lignin blends have been evaluated. Citric acid can act as a compatibilizer and cross-linker for starch and PVOH, and the use of citric acid may retard the diffusion of both oxygen and water vapor if a multilayer coating strategy is used. A polyethylene extrusion coating on a board pre-coated with a recipe containing polyethylene glycol resulted in a greater reduction in the rate of oxygen transmission than through a board pre-coated with a recipe containing citric acid. The addition of lignin to the starch solution decreased the migration of starch from the starch-lignin films, and the addition of ammonium zirconium carbonate as a cross-linker decreased the migration of both starch and lignin from the films. Artikel 4 och 5 ingick som manuskript i avhandlingen