Hybrid Cornstarch and Eggshell Reinforcement for Enhanced Mechanical, Thermal, and Biodegradation Performance of Sustainable Polyvinyl Alcohol Bioplastic

This study developed a novel hybrid polyvinyl alcohol (PVA)-based biofilm system incorporating eggshell (ES) and cornstarch (CS) as natural and waste-derived biofillers, crosslinked with citric acid, and systematically evaluated their synergistic effects on structural, morphological, and functional properties including mechanical strength, thermal, and biodegradability. The novelty lies in combining two distinct biofillers, CaCO ₃ -rich ES and hydrophilic CS, within a PVA matrix to achieve a multifunctional biodegradable film. ES, predominantly composed of CaCO ₃ , and CS, known for its hydrophilic nature, were blended with PVA at varying concentrations (1.0, 2.5, and 5.0 wt.%) using solution casting. Structural characterization confirmed ES as predominantly CaCO ₃ , with essential hydroxyl (−OH) and carbonate (CO ₃ ²⁻ ) groups for matrix interactions. CS showed comparable functional −OH and carbonyls (C = O) groups enhancing PVA matrix compatibility. The biofilm’s biodegradability significantly improved, with PVA films containing 5.0 wt.% CS and ES showing the highest weight losses at 23.13% and 22.40%, respectively. Although the PVACS2.5ES2.5 film exhibited reduced water absorption (247.49%) compared to neat PVA, its WVTR increased to 353.84 g/m ² ·day. This suggests that while the film resists bulk water uptake, its microstructure modified by the hybrid filler network facilitates enhanced vapor permeability through interconnected pores or disrupted polymer chains. Films containing 5.0 wt.% CS and ES achieved tensile strengths of 19.58 MPa and 26.25 MPa, respectively. Thermal analysis showed balanced stability, with a 2.5% CS and 2.5% ES exhibiting T ₁₀ at 59.11°C and T _max at 353.65°C. These findings confirm the potential of the developed biofilm as a multifunctional, sustainable material, where the synergistic reinforcement using dual biofillers offers a novel and scalable pathway to improve PVA bioplastic performance for sustainable packaging. The approach promotes resource circularity through low-cost, bio-based fillers and aligns with global environmental goals.