Ranking plasticizers for polymers with atomistic simulations: PVT, mechanical properties, and the role of hydrogen bonding in thermoplastic starch

Abstract

Virgin biopolymers are often brittle and therefore need the addition of plasticizers to obtain the required mechanical properties for practical applications, for example, in bags and disposable kitchen items. In this article, based on a combined experimental and modeling approach, it is shown that it is possible to rank molecules with respect to their plasticization efficiency (depression in glass transition temperature with PVT data and reduced stiffness and strength) by using molecular dynamics simulations. Starch was used as the polymeric matrix material due to its promising potential as a sustainable, eco-friendly, biobased replacement for fossil-based plastics. Three polyols (glycerol, sorbitol, and xylitol), two ethanolamines (tri- and diethanolamine), and glucose were investigated. The results indicate that molecular simulations can be used to find the optimal plasticizer among a set of candidates or to design/identify better plasticizers in a complex polymer system. Glycerol was the most efficient of the six plasticizers, explained by it forming the least amount of hydrogen bonds, having the shortest hydrogen bond lifetimes and low molecular rigidity. Hence, not only was it possible to rank plasticizers, the ranking results could also be explained by the simulations.