Flow and mixing efficiency characterisation in a CO 2 -assisted single-screw extrusion process by residence time distribution using Raman spectroscopy

•Polyamide foaming with adjustable porosity is achieved by extrusion assisted by CO2.•CO2 introduction has no effect on the flow pattern through the extruder.•In-line Raman spectroscopy was implemented on this process.•Residence time distribution can be accessed by this method.•Static mixer enhances the quantity of CO2 injected and improves the extrudates homogeneity.