Polymer melt rheology

Melt Processing

Every Plastic thermoplastic object manufactured in the world will have gone through the melt stage during its processing. Normally solid plastic polymer pellets will be feed into an extruder or injection moulding machine, where the polymer is melted and then shape formed to create a fibre, film, tube or injection moulded article. Thermoplastic shape forming is a highly developed technology with a huge economic turnover; however a deep scientific and engineering understanding of how thermoplastics behave whilst being processed has only recently started to emerge. With the aid of sophisticated numerical modelling and the choice of a correct viscoelastic constitutive equation it is now possible for engineers to model the way thermoplastic can be processed. This in turn means that existing processes can be improved and new processes discovered not by just trial and error, but by engineering design.

The polymer melt rheology story is one that has been with me  all my academic life. It has involved first observing, using flow birefrengence techniques, the processing flow behaviour of molten polymer. Then, the polymer had to be characterised in the correct way. Then systematic experiments were carried out using the Multipass Rheometer (MPR) that was specifically developed for the task of following polymer processing flow.

Below is a Powerpoint presentation given about the MPR in 2006 at Yamagata Japan

Learn more >Yamagata 2006 (v2) (.pdf)

The final part of the MPR story is told in a seminar presentation given in 2009 at The University of Science abd Technology, Hong Kong.

Learn more >Hong Kong-MPR -09 (.pdf)

There are two movie sequences relevant to the Hong Kong presentation

The MPR movie below shows the flow birefringence processing behaviour of molten polyethylene flowing within a slit. Each dark retardation band measures a certain level of stress within the polymer

The movie below shows the flow birefringence processing behaviour of molten polyethylene flowing within a Cross Slot geometry. Each dark retardation band measures a certain level of stress within the polymer.

Papers relevant to polymer melt rheology are given below