Prediction of plasticization in a real biopolymer system (starch) using molecular dynamics simulations

Virgin biopolymers are often brittle, which means that they need efficient, sustainable, non-toxic plasticizers for most practical applications. Although the mechanical properties of biopolymers plasticized with e.g. sugars have been extensively investigated, the explanation why efficient plasticization normally only occurs above 20 wt% plasticizer is still lacking. In this work, starch/glycerol was used as a model system to show that all-atom molecular dynamics (MD) simulations can be used to capture the transition region at 20–30 wt% plasticizer, where plasticization becomes pronounced. Tensile properties and PVT data (densities and glass transition temperatures) were obtained both from MD simulations and from measurements on real starch/glycerol materials, confirming that MD could capture the experimentally observed transition region. Also, the simulated glycerol diffusivity correlated well with the trends in the mechanical properties. Percolation theory was used to derive a probable explanation of the observed transition. The results indicate that the MD methodology can be used also for other polymer/plasticizer systems and has the potential to be a valuable tool for optimizing the type and amount of plasticizer in a given polymer, as well as being a tool for the design of new efficient plasticizers. [Display omitted] •A molecular simulations methodology was developed to be able to predict plasticization of polymers (tested here on a complex system; thermoplastic starch).•The methodology, and the simulated systems, were evaluated against experimental density, glass-transition data and mechanical properties.•In the simulations, it was possible to observe the transition region where plasticization occurs experimentally (20–30 wt.% plasticizer).•Plasticizer percolation was suggested as a possible cause for the occurrence of the transition region.