Virginia, US – When thermoplastic polyurethane is processed via melt extrusion, solid particulates can form, impacting extrusion performance and often leading to the line having to be shut down. The particles form because of segment aggregation during high temperature processing.
A team led by scientists at Virginia Tech have developed a rheological protocol to enable rapid screening of batches of TPU to predict when particulates may form. It can determine the kinetics of solidification, independent of the supplier or material lot.
They used a combination of rheological, spectroscopic, solubility, light scattering and calorimetric techniques to understand how the solid particulate phase forms during extrusion. They found that endothermic transitions, high degrees of branching, rapid changes in viscoelastic properties and poor dissolution all correlated with the worst extrusion performance.
The suggestion is that the solidification is caused by physical crosslinking through the aggregation of the hard phase. They attributed this to differences in the architecture of polymer branching, high chain mobility, and strain under the conditions required for extrusion. The strong association between solidification and polymer branching, they said, means the characterisation techniques will enable the extrusion performance of TPUs to be screened before processing.
The work has been published in the journal Polymer Degradation and Stability.