Use of Miniemulsion for the Fabrication of Polyhydroxyalkanoate/ZnO Nanocomposite Films via Extrusion or Ultrasonic Spray Coating

Abstract

Polyhydroxyalkanoates show potential as sustainable packaging materials due to their biobased and biodegradable nature. The copolymer poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) stands out for its flexibility and intermediate barrier properties, although novel processing techniques and development of PHBHHx as active packaging material remain relatively unexplored. Incorporation of ZnO nanoparticles (NPs) is a recognized strategy for introducing functional properties, such as UV barrier and antimicrobial activity. However, obtaining optimal dispersion of the nanoparticles remains a challenge. Our research aims to fabricate encapsulated ZnO/PHBHHx particles using a miniemulsion and solvent evaporation technique, which can be further processed using melt processing or ultrasonic spray coating (USSC). Using the miniemulsion technique, ZnO NPs are encapsulated within PHBHHx polymer matrix after optimizing surfactant, ZnO and PHBHHx concentrations. Dynamic Light Scattering indicates an increase in hybrid particle size (186-231 nm) and polydispersity index (0.14-0.24) with ZnO and PHBHHx content, and this with good dispersion quality (TEM), even at high ZnO loadings (40 wt.%). In the first approach, dried hybrid ZnO/PHBHHx particles (40 wt.%) are extruded as masterbatch and hot pressed to fabricate nanocomposite (NC) films. The resulting films, containing 5 wt.% ZnO, show improved dispersion compared to dry mixed NC films (SEM). The NC films display improved UV barrier properties, although strength, stiffness and O2 barrier are slightly reduced as compared with neat PHBHHx films. In the second approach, 0.25 wt.% aqueous inks containing hybrid ZnO/PHBHHx particles are ultrasonically spray coated to yield homogeneous thin coatings (50-100 layers) on PHBHHx film substrates with improved UV barrier. Annealing between 145°C-160°C not only smoothens the layers but also enhances transparency. We conclude that this novel strategy using hybrid particles is highly versatile. The adaptability of these NPs for use in both bulk extrusion and thin coatings highlights a promising avenue for their application in diverse scientific and industrial contexts.