Development and Characterization of Multifunctional Chitosan-Based Composite Films Reinforced with Calcium Chloride, Iron Oxide Nanoparticles, Polyethylene Glycol, and Thymus vulgaris Essential Oil

Objective: This study reports the fabrication and comprehensive physicochemical characterization of advanced functionalized chitosan-based composite films tailored for active food packaging applications. The primary objective was to engineer structurally robust, thermally stable, and biocompatible matrices possessing superior barrier and antimicrobial properties by elucidating the synergistic effects of ionic crosslinkers, plasticizers, and inorganic fillers. Methods: A series of seven distinct formulations were developed by incorporating calcium chloride (CaCl2), polyethylene glycol (PEG-400), and iron oxide (Fe2O3) nanoparticles, both individually and in ternary combinations, into a chitosan matrix. Thymus vulgaris essential oil (1.0 g/100 mL) was systematically encapsulated across all formulations as a potent antimicrobial agent. The structural, morphological, thermal, and barrier properties of the resulting biopolymer networks were rigorously evaluated using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and water vapor transmission rate (WVTR) measurements alongside water absorption kinetics. Results and Discussion: SEM microstructural analysis revealed that while pristine chitosan exhibits a smooth, nonporous, and homogeneous morphology, the integration of CaCl2, PEG-400, and Fe2O3 disrupts surface uniformity, yielding distinct micro-roughness. XRD patterns confirmed a modulation in polymer crystallinity, indicating a controlled transition from amorphous domains into more ordered semi-crystalline phases induced by the additives. Critically, the multicomponent composite networks exhibited superior mechanical integrity and enhanced intermolecular stabilization compared to control films, driven by a highly dense network of hydrogen and coordination bonds. Conclusions: The structural, barrier, and functional performance of these biopolymer matrices can be precisely tuned through strategic compositional adjustments. Among all formulations, the ternary composite film (F7) demonstrated the highest cross-sectional thickness (116.13 µm) accompanied by a minimal swelling index, correlating with an optimized crosslinking density. Crucially, the F7 matrix exhibited exceptional in vitro fungicidal efficacy against Rhizopus stolonifer and Aspergillus niger. All engineered films maintained high optical transparency, macro-homogeneity, and structural uniformity. This work demonstrates that robust interfacial intermolecular and supramolecular interactions dictate the superior thermal and mechanical performance of the developed chitosan-based nanomaterials.