Mechanism of Plasticization and Antiplasticization in Chitosan-Based Systems

Plasticization is often utilized to modify the thermomechanical properties of polymeric materials for various applications. While the effects of plasticizers have been well characterized for a wide array of polymer-additive combinations, the molecular mechanism of plasticization is not fully understood. We employ molecular dynamics simulations to characterize the mechanism of plasticization and antiplasticization in chitosan-based systems with a focus on nanoscale additive-polymer interactions and their effects on the glass transition temperature and elastic properties of the material at various temperatures. We evaluate the validity of previously proposed theories on the plasticization phenomena, and highlight specific chemical moieties that govern the plasticization and antiplaticization mechanism. Furthermore, we investigate the evolution of nano- and macroscale properties at the antiplasticization to plasticization crossover concentration to establish a structure-property relationship. This study aims to help understand the effect of additives in polymer properties and allow more informed design of plasticized systems for applications including pharmaceutics, packaging and agriculture.