2.1.1. Film Thickness and Density

The thickness and density of a formulation are signs of its reliability and the quality preparation process. The film thickness and density values rose as the concentration of EPPE in the gel films increased, as indicated in Table 1. The film density and thickness both changed significantly (*p* < 0.05). Chitosan gel films that had been supplemented with 5% EPPE (Ch-5% EPPE) had the maximum film thickness (0.216 ± 0.08 mm) and density (1.94 ± 0.02 g cm−3 ), whereas control films had the lowest values of thickness (0.132 ± 0.08 mm) and density (1.13 ± 0.02 g cm−3 ) (Table 1). Riaz et al. [27] found a

similar result, reporting that increasing the amount of apple peel polyphenolic extract in the chitosan gel matrix enhances film thickness and density. Peng et al. [28] discovered that with an increased amount of extract added to the film, the interaction between polyphenol components and CH increases. This increasing interaction causes stronger composite binding as the space between both the interacting molecules becomes smaller, enhancing film thickness and density with a rise in the applied EPPE's concentration in the CH-gel matrix.

**Table 1.** Thickness (T), density (D), water vapour permeability (WVP), solubility in water (S), and oil absorption ratio (OAR %) of the chitosan films modified with different percentages of EPPE.

Data are presented as mean ± SD. Means with different superscripts (a–d) in lowercase letters in a column are significantly different at *p* < 0.05.