Gas Permeability Properties of Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

Abstract

Environmental issues, such as the depletion of fossil resources and waste disposal, have instigated the development of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), a biobased and biodegradable polymer, bacterially produced from palm oil. PHBHHx is a versatile polymer and this study aims to further characterize it for the possible application as food packaging material. In this respect, barrier properties for gases such as O2, water vapor and CO2 are of great importance. PHBHHx films were made using compression molding. Results show that the O2 permeability (PO2) of PHBHHx is 6–25 times lower as compared to common low barrier materials such as polypropylene (PP), polyethylene (PE) and polystyrene (PS), close to the PO2 of poly(ethylene terephthalate) (PET) and poly(lactic acid) (PLA), but more than 900 times higher as compared to ethylene vinyl alcohol (EVOH), which is a high barrier polymer used in multilayer packaging. The water vapor permeability of PHBHHx is similar to materials such as PLA, EVOH, polyamide and PET, but slightly higher than more apolar polymers like PP and PE. The CO2 permeability (PCO2) of PHBHHx is lower as compared to PP, PE and PS (2–20 times), but higher as compared to PET (>7 times) and EVOH and poly(vinyl alcohol) (>650 times). In addition, the effect of ambient relative humidity (RH) and temperature on PO2 of PHBHHx was investigated. The results show that PO2 at 23 °C, 0 % RH is increased with 8, 18 and 33 % at RH of 50, 70 and 90 % respectively. At 10 °C, PO2 decreased with 62 %, whereas at 38 °C PO2 increased with 200 % in comparison to PO2 at 23 °C (0 % RH). Overall, it can be concluded that PHBHHx shows potential for certain applications in food packaging, however efforts should be made to further improve the permeability properties.