Characterization of structural and functional properties of ι-carrageenan and/or sodium alginate films: Role of bioactive compound incorporation and CaCl2 crosslinking

There is a lack of comprehension of the structure related properties of specific matrixes important for efficient packaging application. Therefore, this study examines structural, surface and barrier properties of bioactive films composed of two marine issued biopolymers: iota-carrageenan (Car) and sodium alginate (Alg), enriched with natural antioxidants and cross-linking agents (CaCl 2 ). The active films were formulated with chlorogenic acid (CA), D -limonene (DL) and sea fennel (SF) ( Crithmum maritimum ), known for their bioactive potential (against oxygen radicals and microbes). In addition, CaCl₂ was used as a crosslinker to improve the polymer networking, and even more important, moisture resistance. Results showed that the combination of Car and Alg formed interpenetrating polymer networks, improving the water vapor and oxygen barrier. FTIR analysis identified interactions between biopolymer matrices and bioactive molecules. UV-Visible spectroscopy showed improved UV barrier in CA-enriched films. Contact angle measurements and surface free energy analysis confirmed a dominant polar character, particularly in alginate-based blends, with no clear effects of the active molecules. Furthermore, Car-Alg films showed the lowest water vapour permeability, highlighting the role of polymer interactions in reducing permeability despite increased surface hydrophilicity. Crosslinking with Ca²⁺ resulted in higher film cohesion, reducing oxygen permeability. • Interactions between carrageenan and alginate or calcium chloride induce structural changes. • Incorporation of bioactive (antioxidant or essential oil) impacts the network organization. • Carrageenan and alginate complex networks reduce moisture transfers. • CaCl 2 as crosslinker reduces oxygen transfers. • UV barrier properties enhanced by the antioxidant incorporation.