Effect of Ca2+ induced crosslinking on the mechanical and barrier properties of cast alginate films
The use of alginate as a coating material for packaging applications is currently limited due to its difficult processability and high moisture sensitivity. Therefore, this study addresses the crosslinking and scale-up to a continuous application. Three different crosslinking agents were applied: CaCl2 with ethylene diamine tetraacetic acid and two low soluble salts (CaHPO4 and CaCO3). Those were incorporated by internal setting in an alginate matrix with varying Ca2+ concentration ( math formula) and ratio. With the addition of Ca2+, the tensile strength and elongation at break of the cast alginate films increased. This was optimal for a math formula of 0.010-0.015 g (g alginate)−1 dependent on the crosslinking agent. The decrease in water vapor and oxygen permeability due to crosslinking was independent of the crosslinking agent. However, the optimal math formula aiming to decrease permeability was different for the crosslinking agents: CaHPO4 showed best results at a math formula of 0.010 g (g alginate)−1, CaCl2 at 0.012 g (g alginate)−1, and CaCO3 at 0.027 g (g alginate)−1. Upon all analyzed properties CaHPO4 was the most promising crosslinking agent for alginate. Moreover, selected alginate formulations were successfully processed in a continuous lacquering plant. The produced two-layer systems have very low oxygen permeabilities which can be further reduced by crosslinking.