Analysis of the bubble building in with blowing agent loaded polymer melts

• Applicant: Professor Dr.-Ing. Christian Bonten
• Subject Area: Plastics Engineering
• Term: from 2019 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 426052763

Foam structure in extrusion foam experiments is analyzed dependent on physical foam agents, on chemical formulation of the modified strain hardening polymer melts and on the process parameters of the extrusion. The correlation of the extensional properties of the polymer melt can be effected with the bubble and structure building only insufficiently, pure qualitatively, because no realible informations exist about the extensional rates in gas bubbles. No selective modification of the polymers can be taken for foam buildings in order to their extensional viscosity and strain hardening for a controlled bubble building process.Based on these rheological and process specific deficits in order to describe the foam processes is necessary the development or a physical and especially rheological based simulation model for a better prediction of the bubble building in for foaming modified polymers. An experimentally verified bubble building model and a rheological constitutive equation, its parameters can be identified on for foaming modified polymer melts using suitable rheometrical measuring systems, shall be taken. The chemically modified PLA-type shall be characterized rheologically by using rotational, capillary and extensional rheometer systems. Extensional viscosity at extensional rates shall be determined, which are relevant for at the bubble rand equibiaxially stretched polymer melt and a diffusion model shall be developed and applied in order to describe the bubble building process during extrusion foaming.Existing models for the bubble building in with blowing agent loaded polymer melts must be enhanced with a time and strain dependent extensional viscosity function and the relation of the extensional viscosity and the strain hardening with the bubble growth shall be taken into account. For this reason the molecular stress function (MSF) model can be applied and its parameters can be determined from uniaxial extensional experiments. The equibiaxial extensional flow in real bubble building process then can be described correctly with this model.

• DFG Programme: Research Grants