Rheology

The optimization of foam extrusion requires a profound understanding of the rheological properties of polymer melts loaded with a blowing agent. Even small amounts of dissolved blowing agent can lead to a distinct reduction of the viscosity of the melt. The extrusion pressure during foam extrusion generally attains large values. Hence the objective of our research activities is to investigate the influence of the concentration of the blowing agent and pressure on the flow properties of thermoplastic polymers.

Special rheometers are necessary for the determination of the rheological properties of solutions of polymer melts and a blowing agent, since the devices have to withstand elevated pressures and be gas-tight as well. A pressure cell for a rotational rheometer allows the study of the flow properties of gas-saturated polymers at low shear-rates and a especially developed die for a tandem foam-extrusion-setup gives the possibility to conduct experiments at higher shear rates, which are typical for foam extrusion. With both methods deep knowledge on the effect of dissolved blowing-agents in polymer melts on their flow properties is generated.

 

Contact: M.Sc. Dominik Dörr
Phone: +49 921 5574-64
Fax: +49 921 5574-73
Email: dominik.dörr@uni-bayreuth.de

Fig. 1: Picture of the in-line setup for the measurement of gas-loaded polymers in foam extrusion. The setup consists of 1: tandem foam-extrusion line provides the gas-loaded melt, 2: a melt pump ensures a constant flow, 3: the measurement section – a rectangular channel with two pressure transducers to measure the pressure drop and 4: a back-pressure apparatus to keep high pressure levels in the measurement channel.