Fully biobased and biodegradable materials have attracted
a growing
interest in the food packaging sector as they can help to reduce the
negative impact of fossil-based plastics on the environment. Moreover,
the addition of functionalities to these materials by introducing
active molecules has become an essential requirement to create modern
packaging able to extend food’s shelf-life while informing
the consumer about food quality and freshness. In this study, we present
an 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 solvent
casting, increasing the tannin content from 1 to 10 per hundred of
resin (phr). Formic acid was used to reach a homogeneous distribution
of the hydrophilic tannins into hydrophobic PHBV, which is remarkably
challenging by using other solvents. Thanks to their well-known properties,
the effect of tannins on the antioxidant, UV protection, and gas barrier
properties of PHBV was evaluated. Samples containing 5 phr bioadditive
revealed the best combination of these properties, also maintaining
good transparency. Differential scanning calorimetry (DSC) investigations
revealed that films are suitable for application from the fridge to
potentially high temperatures for food heating (up to 200 °C).
Tensile tests have also shown that Young’s modulus (900–1030
MPa) and tensile strength (20 MPa) are comparable with those of the
common polymers and biopolymers for packaging. Besides the improvement
of the PHBV properties for extending food’s shelf-life, it
was also observed that PHBV/tannin could colorimetrically detect ammonia
vapors, thus making this material potentially applicable as a smart
indicator for food spoilage (e.g., detection of fish degradation).
The presented outcomes suggest that tannins can add multifunctional
properties to a polymeric material, opening up a new strategy to obtain
an attractive alternative to petroleum-based plastics for smart food
packaging applications.