FLOW INSTABILITY IN LLDPE PROCESSING AND ITS CONTROL BY FLUOROPOLYMERADDITIVES

Flow instabilities during the capillary extrusion of an octene-LLDPE h ave been measured by signals from an elongational rheometer used to wi nd up the extruding polymer filaments. The presence of fluoropolymers at concentrations above 400 ppm suppressed or eliminated the instabili ty signal, but only after several minutes of extrusion. The time requi red to suppress instability was used as an indicator of additive effec tiveness. Fluoropolymers were found to increase in effectiveness with increasing degree of polarity, as measured by acid/base interaction in dexes and by non-dispersion surface energies. The relative apparent me lt viscosities of host and additive polymer also were involved in effe ctiveness ratings. It is suggested that fluoropolymer additives suppre ss sporadic adhesive failure of the matrix polymer by forming an inter phase between the extruder (die) wall and the flowing bulk polymer.