Sodium-Alginate-Modified Electrospun Cod-Collagen-Peptide Nanofibers: Box–Behnken Process Optimization and Structure–Hydration–Property Correlations in a Chitosan-Supported Composite Mat

Electrospun protein–polysaccharide nanofibers are promising biocompatible substrates for skin-contact materials, yet controlling their morphology and hydration behavior in ternary systems remains challenging. In this work, the modification of a cod collagen peptide/poly(ethylene oxide) (CCP/PEO) system with sodium alginate (SA) was investigated as a model polyelectrolyte interaction. A three-factor Box–Behnken design was applied to optimize the spinning-solution preparation for the liquid absorption capacity (LAC), yielding an optimum at a 12.5 h reaction time, 30 °C, and a 30:1 CCP/SA mass ratio. SEM, FTIR, and XRD analyses indicated that electrostatic association and hydrogen bonding between the protonated amino groups of CCP and carboxylate groups of SA facilitated the formation of uniform nanofibers (458 ± 114 nm) with reduced crystallinity. These interactions significantly enhanced the mechanical performance ( p  < 0.01), with a 13.1% increase in tensile strength and a 27.3% increase in elongation at break. Compared to unmodified controls, the SA-modified composite mats exhibited a ~ 27% higher LAC (1063.9%) and improved water retention after simulated skin contact, despite a moderate reduction in permeability. A three-stage hydration mechanism—comprising capillary substrate uptake, osmotic swelling within the proposed polyelectrolyte network, and nanofiber dissolution—is proposed to explain the enhanced hydration capacity. This study provides a quantitative process map for the design of high-performance dry-state carriers for functional facial masks.