Non-PFAS polymer processing aids: Slip velocity measurements and time-to-clear studies in blown film extrusion

Polymer processing aids (PPAs) reduce and/or eliminate sharkskin melt fracture (MF) instabilities in polyethylene extrusion. This is achieved by increasing the critical flow rate at which MF occurs thus resulting in increased extrusion rate, productivity, as well as reduced energy cost. Fluoropolymers, classified as per- and poly-fluoroalkyl substances (PFAS), have been successfully used as PPAs for several decades but have come under increasing regulatory and consumer scrutiny. Non-PFAS PPAs have been developed and their performance in film extrusion is evaluated in this work. Slip velocity measurements have been carried out using capillary and parallel plate rheometry for the newly developed non-PFAS PPAs as well as a traditional PFAS PPA. A transient flow model has been developed to describe PPA layer thickness build-up and model predictions have been used to correlate experimental observations from time-to-clear (TTC) studies in pilot scale blown film extrusion.