Caffeic acid (CA) molecules were immobilized in a layered inorganic host matrix based on zinc hydroxide structures with different starting interlayer anions, nitrate, and acetate. The chemical composition, structure, thermal stability, morphology, and surface of the host matrices and hybrid compounds were analyzed by X-ray diffraction (XRD), themogravimetric/differencial thermal analysis (TG/DTA), Fourier transform infrarred spectroscopy (FT-IR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Additionally, the surface charge of the materials was investigated using zeta potential at pH ~7. The results show an influence of the surface charge on the chemical, interaction, and structure of the resulting hybrid materials as a function of the starting layered structures. An expansion of the basal spacing to 10.20 Å for zinc hydroxide nitrate (ZHN), and a shrinkage to 10.37 Å for zinc hydroxide acetate (ZHA). These results suggest that the CA lies with a tilt angle in the interlayer region of the inorganic host matrix. The immobilization of CA is favored in ZHN, with respect to ZHA, because a single-layered phase was identified. A higher thermal stability at 65 °C was observed for ZHN-CA than for ZHA-CA. The evaluation of the release behavior showed a higher percentage of CA released from ZHN than ZHA, and the release mechanism was described by the Elovich model. The hybrid materials show potential characteristics for use as bioactive delivery systems.

As the demand for sustainable materials continues to grow, calcium caseinate (Cas) biopolymer films have emerged as promising alternatives to fossil-based plastics. However, their mechanical fragility and high-water sensitivity limit their application in packaging. In this study, we reinforced Cas films with zinc hydroxide nitrate (ZHN) using two incorporation methods: wet (ZHN-w) and dry (ZHN-d). We evaluated how each method affected the dispersion of the filler and, consequently, the functional properties of the films. To our knowledge, this is the first report of ZHN being used in biopolymeric films. Structural and morphological analyses showed better dispersion of ZHN in the wet-incorporated films. These samples exhibited a substantial increase in tensile strength, from 0.75 ± 0.00 MPa to 9.62 ± 2.45 MPa, along with a marked improvement in Young’s modulus. The films also became less soluble in water, more resistant to swelling, and structurally more cohesive. In antimicrobial tests, the ZHN-w films showed stronger inhibition against E. coli and S. aureus. Overall, this approach offers a simple and effective way to enhance protein-based films using food-safe materials, making them suitable for active and bio-based packaging applications.