Effect of rheology and crystallinity on processing and barrier properties of PHA

Abstract

Plastic pollution is one of the major problems that the world is facing at present. Different industrial sectors contribute to this and the packaging sector is one of the main contributors. According to the statistics, the packaging sector alone contributes to 60% of the total plastic pollution. This creates the need for the packaging industry to become more sustainable and produce more environmentally friendly products. There are various types of packaging products and this thesis is focused on food packaging. In food packaging a plastic layer is used to act as a barrier against, for example, gases, such as oxygen and carbon dioxide, and sunlight, as these can decrease the shelf life of the packaged food. However, the plastic film is produced from fossil-based resources and is not biodegradable. The replacement of the conventional plastic barriers with a bio-based polymer is one possible solution to move towards more sustainable packaging materials. For this purpose, a class of bio-based polymers named polyhydroxyalkanoates (PHAs) have been studied in this project. Four different types of PHAs have been characterized using techniques such as DSC, TGA, and DMA, among others. Rheological characteristics were also studied to improve the PHA processing and coating onto paperboard at a pilot scale. Additionally, water vapor barrier properties of the different PHA samples and PHA-coated paperboard were measured and the effect of PHA molecular weight and crystallinity on these was also assessed. From this study, it was observed that PHA with higher molecular weight showed better performance in terms of mechanical properties and barrier properties. Moreover, PHA crystallinity has also been shown to play an important role in terms of barrier properties alongside molecular weight. Regarding rheological properties, it was verified that PHA with higher molecular weight has higher melt viscosity, which makes the material stable at higher temperatures but at the same time, hinders the production of proper coating onto the paper-board. For a better understanding of how PHA processing through extrusion coating can be improved in practice, further studies are required, for instance, the change of processing parameters and the compounding of PHA with other components/ polymers.