The innovative Inline Elongational Rheometer provides real time data on both shear and elongational viscosity, thus improving the capacity to determine melt quality during the extrusion process. It also opens new perspectives for applications in plastics extrusion.
Plastics melt extrusion is an integral part of many supply chains from automotive all the way to recycling.
As established as the process may be, it is exceptionally complex, especially when it comes to monitoring and understanding melt deformation and flow behavior.
Assessing melt quality: offline vs. inline methods
Inline measuring refers to measurements taken during the extrusion process and deliver real time data on pressure, temperature, MFI and IV. Offline measurements conducted outside and subsequent to the production process provide additional data on elongational viscosity.
Inline methods have advantages in terms of time and real time results.
There are various inline rheometers on offer that provide these data. But conventional technologies have a considerable drawback vs. offline analysis: They elicit the MFI value, one point along the viscosity curve. Elongational viscosity is confined to offline laboratory analysis. In addition, the MFI analysis produces material loss, since the sample cannot be returned to the production process.
It is here that the new Leistritz Elongational Rheometer comes in to change the game. For the first time ever, it is possible to measure both shear and elongational viscosity in a single step, in real time and in-line. This is unique and brings a number of technical advantages.
The Leistritz Elongational Rheometer: Innovation on all Counts
The unique new inline rheometer technology was developed in cooperation with the Institute for Polymer Extrusion and Compounding at the Johannes Kepler University in Linz, Austria. It allows the inline analysis of shear and elongational viscosity within the extrusion process – a world first.
This is made possible through a new, patended hyperbolic slotted die. It comprises an intake and ouflow section plus two transition zones. Initially a melt sample is extracted from the extrusion line and diverted into the rheometer. The hyperbolic geometry of the slotted die creates a constant expansion flow, not possible up until now. The die geometry also prevents subsequent expansion, thus avoidoing pressure swirls and dead areas in the flow channel.
The slotted die enables constant monitoring of viscosities with shear rates from 10 to 10.000 s-1 and elongational extension from 5 to 75 s-1. The measurement corridor can be preset. This in turn ensures that both low and high viscosity polymer melts can be analyzed with or without fillers or reinforcing additives.
At the same time it is possible to redirect temperature insensitive melts directly into the extrusion process after measurement. This reduces material loss. Thermically sensitive melts can be channeled out and recovered after measurements.
That sounds promising. But can inline measurement provide data that are comparable to those of offline methods?
In a nutshell: yes! Inline measurement is a logical complement to laboratory methods. Compared to melt analysis in the laboratory, inline measurements provide sufficient accuracy for valid, close-to-process data. This opens up new possibilities. Firstly, there’s a comprehensive documentation on melt quality. Secondly, this is a direct win for melt quality. And last but not least, new fields of applications become technically feasible.
Real time Measurement opens up new Fields of Application
These range from processing polymers, developing new polymer blends all the way to analyzing fiber compounds.
Processing Polymers
Measuring several cycles of polymer melts using the Leistritz Elongational Rheometer clearly shows: both shear and elongational viscosity decline. Ascertaining this inside the production process proves to be a huge advantage, since the data can be accessed for improving melt quality during polymer processing.
Developing of Polymer Blends
Here too, the Leistritz Elongational Rheometer sets the pace in technological development.
Polymer blends help to improve specific material characteristics. So, a blend with impact-copolymers can improve resistance to low temperatures when processing macromolecular polypropylene for injection moulding. Typically a prior blend formulation is developed for this purpose. Up until now, inline measuring of full rheological data was not possible. Melt flow rate is one result but represents only one point on the shear viscosity curve. However, this result is limited and may lead to the wrong conclusions that could result in a waste of material, time and money. It is exactly this loss that the Leistritz Elongational Rheometer helps to prevent. It does so by delivering decisive viscosity parameters in real time, allowing polymer blend quality to be analyzed inside the extrusion process. This, in turn, enables the blend to be adapted and fine-tuned more accurately and quickly than before.
Analysis of Fiber Compounds
The same is true for the analysis of fiber compounds, since elongational viscosity plays an important role. Differences between various PP fiber compounds can be discerned only, when this parameter is established. Being able to do so inline, offers a huge advantage in terms of measuring and quality improvement. The Leistritz Inline Rheometer is thus an important innovation in sensor technology to improve measuring reliability in melt quality analysis.
The Leistritz Elongational Rheometer: Digital Solutions for Tomorrow
The Leistritz Elongational Rheometer not only improves measuring methods and opens up new applications, it was also developed with a focus on usability in industry.
It can be added on to existing extrusion lines and exchanged between various exrtuders, offering you maximum flexibility in aligning your production layouts and opening up new opportunities in operation.
And: it can be fitted to existing Leistritz extrusion lines or to other brands as a stand-alone solution. Options for going online with other data systems is the perfect basis for IoT solutions.