Filler Surface Induced Heterogeneous Nucleation of Polymer Crystals

Switching from non-degradable to compostable plastics can help to reduce global plastic pollution. However, to use compostable plastics in food packaging films, properties including mechanical strength and gas barrier must be optimised. These properties depend on the crystallinity and microstructure of the plastic film, which can be modified by adding filler particles, which act as nucleants for polymer crystallisation [1]. In order to select appropriate fillers, it is necessary to understand the polymer-filler interface.<br/>We use a modified Kremer-Grest polymer model [2] to study crystal nucleation of 20-bead chains. Filler surfaces are modelled using a Lennard-Jones 9-3 potential. The system is cooled from the melt using an NPT ensemble, and the crystal fraction is estimated from straightening of chain segments. Polymer nucleation was observed to occur at the surfaces. Interestingly, this polymer model does not crystallise in simulations without the surfaces. The dependence of crystallisation on the surface-polymer interaction strength, the polymer chain stiffness, and cooling rate will be presented and rationalised in terms of free energy changes. The addition of plasticiser and its effect on nucleation and growth will also be explored. This work provides insight into how filler surfaces can be used to control polymer crystal nucleation and growth, leading to the design of compostable plastics with desired properties.<br/><br/>This work was funded by the Innovate UK Smart Sustainable Plastic Packaging grant (NE/V010603/1). Results were obtained using the ARCHIE-WeSt High Performance Computer (www.archie-west.ac.uk).<br/><br/>[1] Majerczak, Wadkin-Snaith, <i>et al.</i> Polym Int. (2022); https://doi.org/10.1002/pi.6402<br/>[2] G. Grest, K. Kremer, Phys. Rev. A 1986, 33, 3628–3631.<br/>[3] D. Wadkin-Snaith et al. in preparation