Inline-Characterization of Bead Foam Extrusion Processing

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Unlike the established representatives of expandable polystyrene (EPS) and expandedPolypropylene (EPP) most new bead foams are not produced by suspension or in an autoclave process, but continuously by means of foam extrusion coupled to anunderwater granulation. This makes it easier to add additives. Especially thechemical modification (e.g., CE = chain extender) is used in research and industry to increase the melt strength of technical thermoplastics, which is often too low for foaming. In addition to the flexibility, the many parameters also increase the complexity. Furthermore, during the melt processing with the CE reactive processes occur and thus constantly significant material property change. The control of certain final properties is similarly complex when large formulations or thermally sensitive materials are processed. A lot of data from the system and the periphery is already being captured for surveillance; a permanent, systematic recording and evaluation however, does not take place. Furthermore, certain values which are necessary for a scientific evaluation of the process are necessary, but sometimes are not at all or only partially recorded (e.g., melt viscosity, size distribution of the foamed beads). Both quantity and quality can also be increased with appropriate inline analytics.The add-on is necessary (i) to collect all scientifically and technically relevant data in real time and (ii) to evaluate this data - with suitable digital methods - already in real time during the running process. This includes in particular the properties of the final products. Ideally, previously unseen relationships between process and material parameters can be recognized (e.g., correlation of reactivity, rheology and expansion). In addition, a data basis can be created which allows self-optimization of the system through the use of activelearning or machine learning. Through modelling further impulses for understanding and forecasting the behavior of unknown materials are expected. The quality of the analysis is also improved, as becomes evident from the inline rheology is: here, process-relevant (higher) shear rates are measured compared with offline measurement (plate-plate) and the repeated melting during preparation and measurement is no longer necessary, what is critical especially in the case of chemically modified and thermally sensitive samples. The system concept exclusively contains components that allows a digital exchange andrecord and save previously missing measured variables. Material changes can be traced based on pressures, flow behavior and particle sizes (distribution) and process influences. Therefor, an inline rheometer, additional pressure sensors, a particle analyzer and suitable digital peripherals are required.