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Chain orientation in sheared molten poly(ethylene oxide) fractions by measurement of infrared dichroism
Author(s) -
Skytt M.L.,
Jansson J.F.,
Gedde U. W.
Publication year - 1998
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.10326
Subject(s) - materials science , molar mass , shear rate , analytical chemistry (journal) , arrhenius equation , shear (geology) , activation energy , thermodynamics , composite material , rheology , polymer , chemistry , chromatography , physics
Rheo‐infrared spectroscopy was used to study the development of orientation of molten narrow molar mass fractions of poly(ethylene oxide) [molar masses between 18,000 and 120,000 g/mol] during non‐Newtonian shear flow at shear rates between 2 and 270 s −1 and temperatures between 75 and 100°C. The steady state degree of orientation [expressed as the Hermans orientation function ( f ss )] reached a saturation level with increasing shear rate; f ss increased with increasing molar mass ( M ) according to f ss = C 1 − C 2 / M ( C 1 and C 2 are coefficients; the latter depended on shear rate and temperature). The coefficient C 1 ( f ss ) for a polymer with infinite molar mass took a universal value close to 0.05 for the temperatures and shear rates used. Under large shear stresses, the relationship between stress and orientation deviated markedly from linearity. The time to establish a steady state level of orientation was proportional to M 1/2 . The recovery of the isotropic state after the cessation of shear could initially be described by a simple exponential relaxation law: f ∝ e − t /τ r, where τ ρ is the relaxation time. The latter showed a weak molar mass dependence according to τ r ∝ M 0.6 and an Arrhenius temperature dependence with an activation energy of ∼60 kJ/mol. The relaxation of the shear stress after the cessation of shear was more rapid than the recovery of the isotropic state.