Abstract
The main shortcomings of polyhydroxybutyrate (PHB), which is a biodegradable and biocompatible polymer used for biomedical and food packaging applications, are its low thermal stability, poor impact resistance and lack of antibacterial activity. This issue can be improved by blending with other biodegradable polymers such as polyhydroxyhexanoate to form poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), which is a copolymer with better impact strength and lower melting point. However, PHBHHx shows reduced stiffness than PHB and poorer barrier properties against moisture and gases, which is a drawback for use in the food industry. In this regard, novel biodegradable PHBHHx/graphene oxide (GO) nanocomposites have been prepared via a simple, cheap and environmentally friendly solvent casting method to enhance the mechanical properties and antimicrobial activity. The morphology, mechanical, thermal, barrier and antibacterial properties of the nanocomposites were assessed via several characterization methods to show the enhancement in the biopolymer properties. The stiffness and strength of the biopolymer were enhanced up to 40% and 28%, respectively, related to the strong matrix-nanofiller interfacial adhesion attained via hydrogen bonding interactions. Moreover, the nanocomposites showed superior thermal stability (as far as 40 °C), lower water uptake (up to 70%) and better gas and vapour barrier properties (about 45 and 35% reduction) than neat PHBHHx. They also displayed strong biocide action against Gram positive and Gram negative bacteria. These bio-based nanocomposites with antimicrobial activity offer new perspectives for the replacement of traditional petroleum-based synthetic polymers currently used for food packaging.
Highlights
Plastic pollution is a severe threat facing humans, animals and plants
The same tendency is observed for T10 and Tpeak, even with higher increments, by up to 40 ◦C at the highest graphene oxide (GO) loading (Table 1). These results demonstrate that the incorporation of GO increases the thermostability of PHBHHx and is likely related to its high thermal conductivity and heat absorption [36]
Nanocomposites made of biocompatible and biodegradable PHBHHx copolymer and different GO concentrations have been prepared via a simple, cheap and sustainable method of ultrasonication followed by solution casting
Summary
Plastic pollution is a severe threat facing humans, animals and plants. The development of bioplastic materials is imperative in order to solve our global environmental challenges and to preserve the welfare of our world. Many strategies have been assessed to widen the processability of PHAs. One of the approaches is to blend with other polymers such polylactide acid (PLA) [4] and polycaprolactone (PCL) [5] or reinforcing with nanomaterials including organically modified montmorillonite (OMMT) [6], multi-walled carbon nanotubes (MWCNTs) [7], nano-hydroxyapatite (HA) [8] or zinc oxide (ZnO) [9,10]. One of the approaches is to blend with other polymers such polylactide acid (PLA) [4] and polycaprolactone (PCL) [5] or reinforcing with nanomaterials including organically modified montmorillonite (OMMT) [6], multi-walled carbon nanotubes (MWCNTs) [7], nano-hydroxyapatite (HA) [8] or zinc oxide (ZnO) [9,10] It can be polymerised with 3-hydroxyhexanoate units to yield poly(3-hydroxybutyrate-co-3hydroxyhexanoate) (PHBHHx), with a chemical structure shown in Scheme 1
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