Everything in Flow

Polymers can be used industrially in incredibly diverse ways. Depending on the polymer, they possess very good properties for separation processes in membrane technology. The production of polymers is often economical. Polymers also have very good processing properties. We can produce very thin polymer membranes with a high permeability.

Dr. Ulrich Handge, Head of the Department for Material Characterisation and Processing. Photo: HZG/ Christian Schmid

We study a wide range of plastics at the Institute of Polymer Research. We generally use thermoplastic polymers. What are known as block copolymers are very important to our research. They consist of different and often highly incompatible (immiscible) molecular blocks. Under suitable conditions, we can produce a porous sponge-like structure that allows us to separate mixtures of several components. On the basis of block copolymers and an extrusion method – where a polymer liquid is conveyed under pressure through a narrow annular slit die – our department has, for example, managed to spin a hollow fibre that possesses an isoporous outer skin by way of an additional precipitation process. In the future, the hollow-fibre membrane can, for example, be used to filter viruses and bacteria from drinking water. A further application could, for example, be used for medical dialysis systems.

What does that look like in practice?

Porosity and pore size are important parameters for membranes. By controlling the process parameters, we can influence them. With foams, for example, the viscosity is largely responsible for the foam density, the average cell size and for other typical foam properties, such as whether it is an open or a closed-cell foam. In a widely used membrane production process, solvents are utilised in what is known as the phase inversion method. The viscosity of the polymer solution used has a substantial impact on the properties of a hollow fibre membrane. In our department, we also research production methods in which we do not use solvents.

The solvents must be washed from the membrane using a laborious process. In many cases, they can be harmful to one’s health. It is of benefit to the environment every time we refrain from using solvents. Furthermore, it is expensive to treat or dispose of them.

Block copolymer foams with a low foam density can already be produced entirely without the use of solvents right from the melting process. In addition, by means of the sintering process – a processing method in which the temperatures remain below the melting temperature – we can produce functional membranes without solvents. Knowledge of the rheological property as a function of temperature and processing parameters (for example, the deformation rate on a microscopic scale) is again vital for the optimisation of these methods for those polymers used.

The Geesthacht Polymer Days have existed since 2012 and the focus changes annually. They are aimed at industry users as well as university and non-university research institutions. We are concerned with "Practical Polymer Rheology" this year because we know that understanding of flow properties is of great importance in the realm of practice. We want to share our expertise with the users on-site.

We're expecting forty participants altogether, including the speakers, from all over Germany.

The rheology workshop teaches the foundations of rheology (flow and deformation properties) and its deeper connections. Experimental measurement methods, which are very complex, are included in the information that will be highlighted. Photo: Anton Paar Germany GmbH

We wish to examine the foundations in the workshop as well as the deeper theoretical and experimental aspects of rheology. We have therefore invited experienced scientists in this field who can help us offer a comprehensive view of standard and advanced methods of practical rheology. We will initially acquaint participants with the foundations of flow properties, including important concepts and measurement methods. At the same time, we will highlight key relationships in the context of experimental studies. We will then move on to the different properties of polymer solutions and polymer melts. We will deal with experimental methods that are highly complex during the workshop.