DEVELOPMENT OF FUNCTIONAL PVA/CHITOSAN ACTIVE FILMS WITH DIFFERENT TYPES OF ACIDS APPLIED

Plastic packaging represents a highly important segment in the polymer market. Over the years, the search for sustainable packaging has increased with the aim of mitigating environmental problems caused by the accumulation of plastic waste. Active biodegradable films represent promising alternatives to synthetic packaging due to their ability to reduce environmental impacts and add functionality to the materials. Given the above, this study aimed to develop plasticized films based on chitosan (CHI) and polyvinyl alcohol (PVA), and to evaluate the influence of two types of acids (lactic acid - LA and propionic acid - PA), as well as to assess the effect of incorporating cellulose nanocrystals (CNC) on the properties of films added with juçara extract (Euterpe edulis M.). Films were prepared by the casting method, incorporated with different concentrations of CNC (0, 2, 4, 6, and 8%) in a 2% (w/v) acidic chitosan dispersion combined with an aqueous PVA dispersion (0.8% w/v), plasticized with 30% glycerol (w/w) and added with juçara extract (8.78 mL). The materials were characterized for thickness, moisture content, mechanical properties (tensile strength, elongation at break, and Young’s modulus), water vapor permeability, and antioxidant capacity (DPPH). The thickness of the films in LA was approximately 0.15 mm, the elongation was 236%, moisture content was 35%, and the color appeared reddish (due to the predominance of the flavylium cation), exhibiting higher antioxidant activity (up to 95% DPPH radical scavenging). On the other hand, films prepared with PA showed higher stiffness (Young’s modulus of 46.6 MPa), lower moisture content (14%), better water vapor barrier properties, with lower permeability (WVP ≈ 6.7 × 10⁻¹¹ g·m⁻²·s⁻¹·kPa⁻¹) compared to films produced with LA, and a violet coloration (attributed to the presence of less stable forms of anthocyanins, such as the carbinol pseudobase and quinoidal base). Regardless of acid type, CNC addition increased stiffness in both systems. The film structure was also affected by the order and timing of component addition, demonstrating that these factors must be carefully considered in developing functional films. Therefore, lactic acid was considered the most suitable when seeking higher bioactivity and flexibility, while propionic acid conferred better moisture barrier and a more rigid structure, being suitable for applications requiring mechanical strength and lower moisture interaction.