Development of a Rheology Die and Flow Characterization of Gas-Containing Polymer Melts

We present a novel measurement die for characterizing the flow behavior of gas-containing polymer melts. The die is mounted directly on the injection-molding cylinder in place of the mold cavity and thus enables near-process measurement of viscosity (i.e., under the conditions that would be present were a mold attached). This integration also resolves the issue of keeping gas-containing polymer melts under pressure during measurement to prevent desorption. After thermal characterization of the die, various correction approaches were compared against each other to identify the most suitable one for our case. We conducted measurements using polypropylene in combination with two different chemical blowing agents. Increasing the blowing-agent content to up to 6% revealed an interestingly low influence of gases on melt viscosity, which was confirmed by elongational viscosity measurements. For verification, we compared our results to corresponding measurements taken on a high-pressure capillary rheometer and found that they were in excellent agreement. Our die cannot only be used for rheological characterization. Combined with ultrasound sensors, it provides an innovative way of measuring the volumetric flow rate. This development represents an important step in improving the sustainability of gas-containing polymer processing.

Automated summary

This study introduces a novel measurement die for characterizing the flow behavior of gas-containing polymer melts, providing near-process measurement of viscosity and resolving issues related to pressure and desorption. By comparing different correction methods and conducting measurements on polypropylene with blowing agents, it was found that gases had a low impact on melt viscosity. The die, when combined with ultrasound sensors, offers an innovative method for measuring volumetric flow rate, representing an important advancement in improving the sustainability of gas-containing polymer processing.