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Abstract
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.
Highlights
Against the backdrop of climate change, sustainability has become a prime objective [1,2]
Before the experiments with CBAs, our rheology die for injection molding had to pass thermal characterization tests
For measurements of elongational viscosity, a special die was mounted on an extruder
Summary
Against the backdrop of climate change, sustainability has become a prime objective [1,2]. In 2015, with a total worldwide production of 322 million metric tons, the two most important polyolefins (polyethylene (PE) and polypropylene (PP)) had a combined market share of over 50% [3]. (ii) the possibility of integrating many functions into a single component, and (iii) their energy-saving and economical production and processing. Aspect (iii) in particular is closely related to the flowability (and the viscosity) of polymer melts. Understanding the rheology of gas-containing polymer melts is essential in polymer processing (for machine selection, mold design, etc.). Since accurate data improve the capabilities of simulations (e.g., in injection molding), the general objective is to measure viscosity as close to the process as possible
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