Mechanical and barrier properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or poly(lactic acid)-based films with active coating

Biodegradable synthetic polymers exhibit high mechanical resistance and good water vapor barrier properties; however, they present limitations such as high oxygen permeability, which hinders their application. In this context, protein-based coatings with high oxygen barrier incorporating active compounds allow the development of materials with complementary functional properties. The objective of this study was to analyze the functionality of protein-based coatings (gelatin or sodium caseinate) with or without the incorporation of emulsified rutin and carvacrol in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) or poly(lactic acid) (PLA)-based films obtained by termocompression. Furthermore, the films were characterized according to their main mechanical properties, including tensile strength (TS), elastic modulus (EM), elongation at break (EB), and seal strength (SS), as well as their barrier properties, such as water vapor permeability (WVP) and oxygen permeability (OP). The protein coating on PHBV and PLA-based films decreased OP (55% and 85%, respectively) and TS (30% and 18%, respectively), while increasing EB (59% specifically in PHBV films). PHBV-based films with protein coatings exhibited the highest water vapor and oxygen barrier (reduction of 86% in WVP and 27% in OP compared to the coated PLA films), properties that were further improved by the incorporation of active compounds. Meanwhile, PLA-based films showed higher TS and SS values, which decreased in the active films. The gelatin-based protein coating provided greater barrier properties and sealing strength to the PHBV and PLA-based films. The obtained results offer an interesting alternative for developing resistant biodegradable active films with enhanced barrier properties for future applications as food packaging materials.