A semi-empirical model for predicting the maximum spreading factor, βmax of chitosan/PVA bio-coating droplets on hydrophobic banana peel surfaces

The behavior of droplets from chitosan/polyvinyl alcohol (CS/PVA) bio-coatings upon impact with hydrophobic biological surfaces plays a critical role in determining coating uniformity and effectiveness. This study investigates the maximum spreading factor, βmax of CS/PVA droplets deposited on fresh banana peel surfaces, which are inherently hydrophobic due to their waxy cuticle layer. Droplets with varying CS/PVA compositions were characterized in terms of viscosity, surface tension, and density. A series of high-speed imaging experiments was conducted to analyze droplet dynamics during impact, while dimensionless numbers, Weber (We), Ohnesorge (Oh), and Reynolds (Re) numbers were experimentally determined. Results revealed a nonlinear increase in βmax with We, modulated by Oh, leading to the formulation of a new empirical correlation model, βmax=1.0+a[We.Re]0.2, where a=1.4Oh+0.21. The model demonstrated high predictive accuracy (R² = 0.943–0.968) and outperformed existing energy- and momentum-based correlation models. This work provides a robust, scalable framework for modeling droplet spreading on biologically relevant hydrophobic surfaces, supporting the rational design of bio-based coatings in sustainable food packaging and agricultural applications.