Plastics. Determination of the fluidity of plastics using capillary and slit-die rheometers
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1 Scope This International Standard specifies methods for determining the fluidity of plastics melts subjected to shear stresses at rates and temperatures approximating to those arising in plastics processing. Testing plastics melts in accordance with these methods is necessary since the fluidity of plastics melts is generally not dependent solely on temperature, but also on other parameters, in particular shear rate and shear stress. The methods described in this International Standard are useful for determining melt viscosities from 10 Pa∙s to 10 7 Pa∙s, depending on the measurement range of the pressure and/or force transducer and the mechanical and physical characteristics of the rheometer. The shear rates occurring in extrusion rheometers range from 1 s −1 to 10 6 s −1 . Elongational effects at the die entrance cause extrudate swelling at the die exit. Methods for assessing extrudate swelling have also been included. The rheological techniques described are not limited to the characterization of wall-adhering thermoplastics melts only; for example, thermoplastics exhibiting “slip” effects [ 1 ][ 2 ] and thermosetting plastics can be included. However, the methods used for determining the shear rate and shear viscosity are invalid for materials which are not wall-adhering. Nevertheless, this International Standard can be used to characterize the rheological behaviour of such fluids for a given geometry.
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