Influence of polymer compatibility and layer thickness on the structural and thermophysical properties of polymer multilayer films

Abstract

Coextruded multilayer polymer films are promising packaging materials since their architecture and properties can be adjusted while the production technology is environmentally friendly. Here, the effect of layers thickness and polymers compatibility in alternating layers on the structure and thermophysical properties of such films was studied by means of molecular dynamics simulations. The results show that the model films with layers of incompatible polymers polylactide (PLA) and polyethylene (PE) are stable in time and have very low interfacial diffusion depth even when the layers thickness is about several nanometers. Systems with incompatible polymers differ from the systems with compatible ones by the presence of anisotropy in the mobility of polymer atoms. These films also have two glass transition temperatures. Multilayer films based on compatible for the selected chain lengths polymers PLA and poly(3-hydroxybutyrate) (PHB) as well as one-component systems with PLA layers have a single glass transition point. In these films interfacial diffusion depth tends to gradually increase during the simulation. However, even for one-component system with layers thickness of 7.5 nm sufficiently stable structure of the film is formed, while heterogeneous films with PLA and PHB layers reach metastable state during the modeling with almost constant interfacial diffusion depth.