Thermodynamic Parameters for Predicting Adhesion Between Functional Polyethylenes to Polystyrene Copolymers

Polystyrene and polystyrene copolymers have many unique properties that make them desirable for use in flexible packaging. Polystyrene monofilms however are not practical for use on high-speed packaging lines due to their poor heat sealability and flex cracking. Coextruded films of polystyrene with polyethylene combine the desirable properties of polystyrene with polyethylene. Still, PS coextrusions with PE are not commonplace due partly to the manufacturing challenges and partly due to the paucity of adhesives that can bond PE to PS in coextruded films. This paper focuses on the adhesion challenges at the PS-PE interface. We will review fundamental principles of adhesion at the coex interface, present results from adhesion screening studies of a styreneacrylic copolymer with various polyethylenes and investigate the use of thermodynamic parameters as an aid to predict or estimate the magnitude of chemical bonds at the interface. The specific approach is based on the early work of Fowkes who forwarded the theory that interfacial adhesion is fundamentally governed by Acid-base interactions and dispersion forces.