Characterization of Interdiffusion Between Different Co Extruded Polymers via Confocal Raman Microscopy

In polymer multilayer materials, the adhesion between the individual layers is an essential feature governing the overall product quality. For compatible polymer pairs, the interpenetration of the macromolecules across the interface, the so-called interdiffusion, is the main adhesion mechanism and the resulting interdiffusion layer thickness is a measure for the adhesive strength. To gain insight into the occurrences at polymer-polymer interfaces, especially under processing conditions, methods to characterize the diffuse interphase are necessary. Confocal Raman microscopy proves to be an excellent tool for this application. In this work, a measurement and evaluation procedure to determine the diffusion profiles and the thickness of the interdiffusion layer based on Raman imaging is developed and illustrated for the highly compatible polymer pair PMMA and SAN. For diffusion experiments under static conditions, the influence of contact time and temperature is shown and the additional effect of interfacial shear stress is established for co -extruded samples. Based on these findings, an enhanced understanding of phenomena at co -extruded polymer-polymer interfaces can be acquired, which benefits the development of novel multi -layered products.