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Extrusion die swell of carbon black‐filled natural rubber
Author(s) -
Bagchi Anoop K.,
Sirkar Kamalesh K.
Publication year - 1979
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1979.070230608
Subject(s) - die swell , natural rubber , materials science , carbon black , extrusion , composite material , swell , volume fraction , shear stress , shear modulus , elastomer , die (integrated circuit) , rheometer , deformation (meteorology) , shear (geology) , shear rate , extrusion moulding , rheology , thermodynamics , physics , nanotechnology
Extrusion die swell of natural rubber compounded with a wide variety of carbon blacks has been determined in a capillary rheometer using a long circular die. The range of variation of carbon black loading, surface area, and structure are, respectively, 10 to 60 phr, 44 to 124 m 2 /g, and 78 to 120 cc/100 g. The effective carbon black volume fraction φ e not participating in the strain recovery leading to die swell is assumed to be the sum of the actual filler volume fraction and the fraction of unextractable rubber determined experimentally for each compound. Bagley and Duffey's analysis of extrusion die swell of unfilled polymers as unconstrained elastic recovery was adopted for a filled elastomeric system whose relative shear modulus ( G / G 0 ) is assumed to vary as (1 − φ e ) − N . The matrix shear modulus G 0 , originally introduced by Nakazima and Shida on the basis of a linearized approximation, will depend on the shear stress level because of nonlinear deformation. The power N will vary with shear stress which changes the orientation of carbon black aggregates. Except for these features, die swell data for a wide range of carbon black compounds fall on a single curve when plotted in the manner of the predicted relation between the wall shear stress, die swell, and φ e . Replacing φ e by Medalia's φ′ based on an equivalent sphere concept introduces a larger scatter around the mean curve.