An Experimental Study of Polymer-Polymer Interdiffusion under Co-Extrusion Processing Conditions
Sprache des Vortragstitels:
38th International Conference of the Polymer Processing Society (PPS-38)
Sprache des Tagungstitel:
Interdiffusion ? defined as the mutual interpenetration of macromolecules to form a diffuse interphase ? is observed at polymer-polymer interfaces in a wide range of plastics processing techniques. This transport phenomenon has been studied extensively on static interfaces (i.e., the polymers and, in particular, the interface is not subject to deformation rates), for instance, in plastics welding, 3D printing, and consolidation of thermoplastic UD tapes. In contrast, interdiffusion under shear-loaded conditions as present in stratified flows during co-extrusion has been studied scarcely to date. Under real co-extrusion processing conditions, employing a two-layer co-extrusion demonstration die and the material combination PMMA and SAN, this work presents the effect of interfacial contact time, of extrusion melt temperature, and of the magnitude of the interfacial shear stress on the interdiffusion rate. The implemented model-based digital process twin enabled accurate adjustment of the magnitude of aforementioned process parameters in the die. The diffuse interphase of the calibrated two-layer sheets was then characterized spectroscopically by means of confocal Raman microscopy. By measuring the breadth of the diffuse interphase region and deriving the mutual interdiffusion coefficient we revealed that ? similar to static conditions ? interdiffusion during co-extrusion flows scales with contact time and temperature according to Fick?s laws and an Arrhenius relationship, respectively. Moreover, already low interfacial shear stresses significantly boosted the rate of interdiffusion compared to static conditions. Though, a systematic variation of interfacial shear stress levels between approximately 1,000 and 40,000 Pa showed no further impact on the mutual interdiffusion coefficient (i.e., rate of interdiffusion).