Multifunctional poly(3-hydroxybutyrate) composites with MoS₂ for food packaging applications

Bacterial poly(3-hydroxybutyrate) (PHB) was reinforced with MoS₂ nanosheets for developing multifunctional polymer composites toward active and smart packaging applications. The tensile elastic modulus was drastically increased at low concentrations of filler, even by a factor of 2.0 at only 0.5 wt% of MoS₂, barely affecting the elongation at break. The nanoparticles further modified the surface characteristics of the PHB, increasing the wettability at low concentrations and reducing its roughness and topography. Regarding the barrier properties, 0.5 wt% of MoS₂ reduced around 65 % of both the oxygen and water vapor permeability, although at higher concentrations these values increase even to higher values than the pure matrix. The MoS₂ nanoparticles also increased the biodegradation of PHB, with the fastest degradation observed at 3.0 wt%. The high near-infrared absorption of MoS₂ particles further allowed a simple and low-powered route to produce sub-millimetric perforated and breathable PHB films further controlling the UV–vis radiation absorption. Noteworthy, the composites can be used for capacitive humidity sensors through an interdigitated electrode structure with a 100 % increase in the sensitivity arising from their higher dielectric constant. Regarding the antibacterial behavior, while the presence of MoS₂ did not affect the viability of gram-negative Salmonella Typhi, the composite with 3.0 wt% of MoS₂ reduced the survival of gram-positive Listeria monocytogenes without any external stimulus. These results show that the addition of MoS₂ nanosheets into PHB is a proper route to extend the applications of this biodegradable and compositable polymer, specially toward active and smart packaging applications.