Recyclability of poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBH) for food packaging applications

This study is the first to investigate the recyclability of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), a small chain length PHA, and evaluate the gas barrier properties of the recycled materials. A recycling simulation of PHBH was performed through five twin-screw extrusion cycles. Although the onset degradation temperature and the chemical structure of the processed PHBH remained stable, size exclusion chromatography and melt flow index revealed a drop of 24.3% in the molar mass of the recycled materials. However, the recycled samples showed higher impact strength and, therefore, are less brittle and more elastic. Gas barrier properties of PHBH were found to enhance after the first recycling step. A significant decrease in both permeability and diffusion coefficients was observed after the first extrusion cycle. At the same time, the calculated mean integral diffusion coefficient  as well as the plasticization factor (γCeq) demonstrate a weak water plasticization effect for recycled materials.