Fully Biobased Polyhydroxyalkanoate/Tannin Films as Multifunctional Materials for Smart Food Packaging Applications

Fully biobased and biodegradable materials have attracteda growinginterest in the food packaging sector as they can help to reduce thenegative impact of fossil-based plastics on the environment. Moreover,the addition of functionalities to these materials by introducingactive molecules has become an essential requirement to create modernpackaging able to extend food's shelf-life while informingthe consumer about food quality and freshness. In this study, we presentan innovative bioplastic formulation for food packaging based on poly-(hydroxybutyrate-co-valerate) (PHBV) and tannins as multifunctional additives.As a proof of concept, PHBV/tannin films were prepared by solventcasting, increasing the tannin content from 1 to 10 per hundred ofresin (phr). Formic acid was used to reach a homogeneous distributionof the hydrophilic tannins into hydrophobic PHBV, which is remarkablychallenging by using other solvents. Thanks to their well-known properties,the effect of tannins on the antioxidant, UV protection, and gas barrierproperties of PHBV was evaluated. Samples containing 5 phr bioadditiverevealed the best combination of these properties, also maintaininggood transparency. Differential scanning calorimetry (DSC) investigationsrevealed that films are suitable for application from the fridge topotentially high temperatures for food heating (up to 200 degrees C).Tensile tests have also shown that Young's modulus (900-1030MPa) and tensile strength (20 MPa) are comparable with those of thecommon polymers and biopolymers for packaging. Besides the improvementof the PHBV properties for extending food's shelf-life, itwas also observed that PHBV/tannin could colorimetrically detect ammoniavapors, thus making this material potentially applicable as a smartindicator for food spoilage (e.g., detection of fish degradation).The presented outcomes suggest that tannins can add multifunctionalproperties to a polymeric material, opening up a new strategy to obtainan attractive alternative to petroleum-based plastics for smart foodpackaging applications.