Abstract
A knowledge of the complete flow curve or rheogram of a polymeric melt depicting the variation of the melt viscosity over industrially relevant range of shear rate and temperature is essential in the design of polymer processing equipment, process optimization and trouble-shooting. These data are generated on sophisticated rheometers that are beyond the financial and technical means of most plastics processors. The only flow parameter available to the processor is the melt flow index of the material.
In the present work, a method has been proposed to estimate the rheograms of a melt at temperatures relevant to its processing conditions with the use of a master curve, knowing the melt flow index and glass transition temperature of the material. Master curves that coalesce rheograms of different grades at various temperatures have been generated and presented for low density polyethylene, high density polyethylene, polypropylene, polystyrene and styrene-acrylonitrile copolymer.
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Abbreviations
- D :
-
diameter of the tube (cm)
- K, K′ :
-
constants
- l :
-
length of the tube (cm)
- L :
-
weight of piston and load (kg)
- MFI:
-
melt flow index (g/10 min)
- ΔP :
-
pressure drop through tube (dynes/cm2)
- Q :
-
volumetric flow rate (cm3)
- T 1 :
-
temperature at condition 1 (K)
- T 2 :
-
temperature at condition 2 (K)
- T g :
-
glass transition temperature (K)
- T s :
-
standard reference temperature (K) (=T g + 50 K)
- V :
-
average velocity (cm/s)
- W :
-
weight rate of flow (g)
- \(\dot \gamma \) :
-
shear rate (s−1)
- \(\dot \gamma _a \) :
-
apparent shear rate (s−1)
- η 1 :
-
viscosity at condition 1 (poise)
- η a :
-
apparent viscosity (poise)
- η s :
-
viscosity at standard temperature (poise)
- ρ :
-
density (g/cm3)
- τ :
-
shear stress (dynes/cm2)
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NCL Communication Number 2903.
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Shenoy, A.V., Chattopadhyay, S. & Nadkarni, V.M. From melt flow index to rheogram. Rheol Acta 22, 90–101 (1983). https://doi.org/10.1007/BF01679833
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DOI: https://doi.org/10.1007/BF01679833