Flow Induced Coating of Fluoropolymer Additives: Development of Frustrated Total Internal Reflection Imaging
S B. Kharchenko, P M. McGuiggan, Kalman D. Migler
In the extrusion of linear low-density polyethylene (PE), fluoropolymer-processing additives (PPA) are used to eliminate the surface defect known as sharkskin by coating the die wall and inducing slip at the PPA/PE interface. We describe an in situ optical method for measurement of the coating thickness by exploiting the phenomenon of frustrated total internal reflection (frust-TIR). By correlating the optical and pressure measurements, extrudate appearance and auxiliary experiments we can elucidate the kinetics of the coating process. The PPA droplets adsorb at the die entrance region and migrate under the shear stress to the capillary exit where sharkskin is eliminated. We find that a uniform coating in the range of (25 to 60) nm is sufficient for sharkskin elimination. The steady state coating thickness ranges from (200 to 350) nm depending on shear rate and concentration.
, McGuiggan, P.
and Migler, K.
Flow Induced Coating of Fluoropolymer Additives: Development of Frustrated Total Internal Reflection Imaging, Journal of Rheology, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=852181
(Accessed December 9, 2023)