Visualizing the Elimination of Sharkskin Through Fluoropolymer Additives: Coating and Polymer-Polymer Slippage
Kalman D. Migler, C LavallTe, M P. Dillon, S S. Woods, C L. Gettinger
We developed a capillary rheo-optics technique to visualize the mechanism by which fluoropolymer additives eliminate a distortion called sharkskin in the extrudate of linear low density polyethylene (LLDPE). The measurements were carried out in a transparent sapphire tube located at the exit of a twin-screw extruder. Depth resolved optical microscopy was used to measure the polymer velocity profiles and also to image the coating process of the polymer processing additive (PPA) onto the capillary wall. In the absence of PPA, no slippage occurs between the capillary wall and the polyethylene; sharkskin was observed at all flow rates. Upon addition of the PPA to the LLDPE, the PPA migrates to the capillary wall where it sticks and induces slippage between itself and the LLDPE, concomitant with the elimination of sharkskin. The interface between the PPA and LLDPE is characterized by long stripes in the flow direction. Large values of the polymer-polymer slippage parameter were found which indicate that the fluoropolymer and LLDPE are fully disentangled at their interface. The PPA dramatically reduces the extensional deformation at the exit surface.
extrusion, fluoropolymer, polymer process additive, sharkskin, slippage
, LavallTe, C.
, Dillon, M.
, Woods, S.
and Gettinger, C.
Visualizing the Elimination of Sharkskin Through Fluoropolymer Additives: Coating and Polymer-Polymer Slippage, Journal of Rheology, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=851767
(Accessed December 8, 2023)