ISO 11443:2005 specifies methods for determining the fluidity of plastics melts subjected to shear stresses at rates and temperatures similar 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 only on temperature, but also on other parameters, in particular shear rate, shear stress, molecular weight, filler content. The shear rates occurring in extrusion capillary rheometers range from 1 s-1 to 106 s-1, and the capillary rheometers are able to cover the full range of processing conditions including extrusion and injection moulding.
When asked to solve a flow problem occurring during the extrusion of different types of PP samples and to help optimizing the process, we used our SR 50 to measure the rheological curve of the materials that contain different types of fillers and additives. The fillers are commonly used to reinforce the PP raw polymer and to give better mechanical properties to the finished product. They are also used to influence the flow behavior by increasing the viscosity, making the flow much more difficult than with the pure polymer.
To help solve processing problems like the onset of surface defects due to excessive processing speed (shear rate) or of thermal degradation due to temperature increase, we suggest adding some additives or lubricants (processing aids) to the material to help modifly the flow behavior. Our capillary rheometer is ideal for measuring the change of rheological properties, and to identify the optimum material formulation, by comparing the different materials viscosity at high rates of deformation exactly in the process conditions.