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Lower Newtonian viscosities of polystyrene
Author(s) -
Chee K. K.,
Rudin A.
Publication year - 1971
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.760110107
Subject(s) - shear rate , materials science , shear stress , non newtonian fluid , critical resolved shear stress , newtonian fluid , shear (geology) , generalized newtonian fluid , simple shear , dilatant , apparent viscosity , shear modulus , viscometer , shear flow , pure shear , thermodynamics , mechanics , composite material , viscosity , physics
A falling coaxial cylinder viscometer was used to measure the melt flow behaviour of a commercial polystyrene with Mw 260,000. The shear stress region extended down to 0.6 × 10 4 dynes/cm 2 and shear rates were as low as 3 × 10 −2 sec −1 at 186°C. The shear rate‐shear stress plots were linear at low shear stresses with slopes (differential viscosities) of 3.3 × 10 5 poises at total shear less than 120 units and decreasing differential viscosity with higher total shear. The flow curves at relatively low total shear were initially dilatant and became pseudoplastic with increasing shear stress. The inflection point represents a Newtonian apparent viscosity, which agrees fairly well with literature values for polystyrenes of the same Mw . Newtonian apparent viscosity is characteristic of a point value of shear stress and shear rate and is not necessarily a plateau region. Observation of a Newtonian region with decreasing shear stress or shear rate does not prove that this flow regime persists unchanged to zero values of the experimental parameter. The existence and magnitude of the Newtonian apparent viscosity reflects shear history of the polymer as well as its constitution and molecular weight distribution.