Flow Instability in LLDPE Processing and Its Control by Fluoropolymer Additives

Flow instabilities during the capillary extrusion of an octene-LLDPE have been measured by signals from an elongational rheometer used to wind up the extruding polymer filaments. The presence of fluoropolymers at concentrations above 400 ppm suppressed or eliminated the instability signal, but only after several minutes of extrusion. The time required to suppress instability was used as an indicator of additive effectiveness. Fluoropolymers were found to increase in effectiveness with increasing degree of polarity, as measured by acid/base interaction indexes and by non-dispersion surface energies. The relative apparent melt viscosities of host and additive polymer also were involved in effectiveness ratings. It is suggested that fluoropolymer additives suppress sporadic adhesive failure of the matrix polymer by forming an interphase between the extruder (die) wall and the flowing bulk polymer.

[1]  S. Hatzikiriakos,et al.  Role of slip and fracture in the oscillating flow of HDPE in a capillary , 1992 .

[2]  H. Schreiber,et al.  On the evaluation of surface interactions by inverse gas chromatography , 1992 .

[3]  S. Hatzikiriakos,et al.  Wall slip of molten high density polyethylenes. II. Capillary rheometer studies , 1992 .

[4]  S. Hatzikiriakos,et al.  Wall slip of molten high density polyethylene. I. Sliding plate rheometer studies , 1991 .

[5]  H. Schreiber,et al.  New approaches to the processing of rutile‐filled polyolefins , 1990 .

[6]  M. Denn,et al.  On the apparent relation between adhesive failure and melt fracture , 1990 .

[7]  H. Schreiber,et al.  Some properties of polyethylene compounds with surface‐modified fillers , 1990 .

[8]  J. Piau,et al.  Influence of upstream instabilities and wall slip on melt fracture and sharkskin phenomena during silicones extrusion through orifice dies , 1990 .

[9]  J. Agassant,et al.  Characterization of the Sharkskin Defect and its Development with the Flow Conditions** , 1989 .

[10]  Douglass S. Kalika,et al.  Wall Slip and Extrudate Distortion in Linear Low‐Density Polyethylene , 1987 .

[11]  A. V. Ramamurthy.  Wall Slip in Viscous Fluids and Influence of Materials of Construction , 1986 .

[12]  Y.‐H. Lin.  Explanation for Slip‐Stick Melt Fracture in Terms of Molecular Dynamics in Polymer Melts , 1985 .

[13]  E. Papirer,et al.  Gas-solid chromatography: a quick method of estimating surface free energy variations induced by the treatment of short glass fibers , 1983 .

[14]  Viktor Gutmann,et al.  The Donor-Acceptor Approach to Molecular Interactions , 1978 .

[15]  P. Dynes,et al.  Surface Energy Analysis of Treated Graphite Fibers , 1974 .

[16]  T. W. Huseby.  Hypothesis on a Certain Flow Instability in Polymer Melts , 1966 .

[17]  E. B. Bagley,et al.  Discontinuity in the Flow Curve of Polyethylene , 1958 .

[18]  J. Tordella.  Fracture in the Extrusion of Amorphous Polymers through Capillaries , 1956 .

[19]  M. Mooney.  Explicit Formulas for Slip and Fluidity , 1931 .