Biocomposite design for food packaging

Plastic waste has a hugely detrimental impact on the environment and there is mounting pressure on industry to replace traditional polluting petrochemical polymers with sustainably-sourced polymers. Plastic film food packaging, while single-use, plays an important role in extending the shelf life of food and reducing food waste that is a significant contributor to greenhouse gases. While plastic films are typically made from recyclable polymers most plastic film food packaging is neither biodegradable nor recyclable due to food contamination. Therefore, if films can be designed to have the appropriate properties, be sustainably-sourced and biodegradable, these sustainable polymer films would be a much better alternative for food packaging applications and result in a large reduction in the amount of plastic ending up in landfill.

There are many sustainably-sourced and biodegradable polymers. Nevertheless, the switch to sustainable polymer films is challenging due to a number of factors, not least of which is their poor performance in comparison to petrochemical polymers. If we are able to drive the performance properties of the sustainable polymer films up to the levels of the petrochemicals, consumer and industry demand combined with government incentives will in turn drive large-scale production and lower cost manufacturing. It is, therefore, a matter of urgency to improve sustainable polymer film performance to enable its wide-spread uptake. The performance and processability of sustainable polymer films can be improved by the addition of filler particles and plasticisers, respectively, to form a composite material. While there are numerous studies of specific biodegradable polymer composites (which we name biocomposites) in the scientific literature, progress has been slow owing to a lack of rational design.

To increase the shelf life of food, composite packaging films must act as a gas and moisture barrier. The films must also be chemically and thermally stable, have sufficient mechanical strength and flexibility, and transparency so they are aesthetically pleasing to the consumer. From the manufacturing perspective the films must be easily processible. Good barrier properties typically require a high degree of polymer crystallinity. Yet, film flexibility and transparency are also important attributes and require that the crystallites are not too large, potentially reducing crystallinity. The presence of filler particles can either induce or hinder polymer crystallinity, depending on the interaction of the particles with the polymer. The film's microstructure, caused by the spatial arrangement of the polymer crystallites within it, then dictates the large-scale properties such as flexibility, transparency and gas barrier.

We propose that crystallinity can be controlled via the interfacial properties and coupling agent, that the microstructure can be controlled through interface properties and processing, and that the composite performance can be controlled through the microstructure. We also expect that the design guidelines will be transferable to other biocomposites. In this project, we will use molecular dynamics simulations to model polymer crystallisation near the filler particle interface. Mesoscale (e.g. finite element and Monte Carlo) modelling will be used to simulate the resulting microstructure. The modelling, combined with experimental preparation, characterisation, and performance measurements, will enable the interface properties and processing steps to be connected to the material properties. The project outcomes will be: 1) identification of biocomposites suitable for thin film food packaging, 2) increased understanding of how filler particles affect polymer crystallization and microstructure, 3) design rules for accelerated biocomposite development, and 4) establishing the pathway for the uptake of the design rules and new materials by industry.