PROCESSING | INLINE MEASUREMENT
Above: The Leistritz hyperbolic die geometry prevents subsequent expansion, avoiding pressure swirls and dead areas in the flow channel
drawback in that they provide an MFI value at just one point along the viscosity curve. Elongational viscosity has to be determined using offline laboratory analysis. In addition, the MFI analysis results in material loss, since the sample cannot be returned to the production process. The Leistritz rheometer technology allows inline analysis of shear and elongational viscosity within the extrusion process, which is made possible through its hyperbolic slotted die. This comprises an intake and outflow 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 and prevents subsequent expansion, avoiding pressure swirls and dead areas in the flow channel. The slotted die enables constant monitor- ing of viscosities with shear rates from 10-10.000 s-1 and elongational extension from 5-75 s-1
. The measurement corridor can be pre-set, which
Above: Leistriz says its inline rheometer (centre in this image) is designed to be easily switched between lines
approaches in the area of AI.” Manufacturers of inline measuring systems meet
these requirements and are offering increasingly attractive solutions, they say. As a manufacturer of compounding and extrusion systems, Coperion is already working with many established manufactur- ers of inline measurement technology. The company aims to be technologically open to any supplier and supports the integration of these solutions into Coperion compounding and extrusion systems by offering the hardware and software solutions for its twin-screw extruder and peripheral devices.
Inline rheometry
Germany-based compounding extrusion specialist Leistritz Extrusion Technology introduced its Inline Elongational Rheometer to provide real time data on both shear and elongational viscosity, improving the capacity to determine melt quality during the extrusion process. Developed in cooperation with the Institute for Polymer Extrusion and Compounding at the Johannes Kepler University in Linz, Austria, the technology was launched in 2018 and considerable application expertise has been accumulated since then. According to Leistritz, there are various inline rheometers that provide pressure, temperature, melt flow index (MFI) and intrinsic viscosity (IV) data. But conventional technologies have a
32 COMPOUNDING WORLD | November 2021
ensures that both low and high viscosity polymer melts can be analysed with or without fillers or reinforcing additives. It is also possible to redirect temperature insensitive melts directly into the extrusion process after measurement, which reduces material loss. Thermically sensitive melts can be channelled out and recovered after measurements. Leistritz says inline measurement is a logical complement to laboratory methods and opens up new possibilities. Firstly, it provides comprehensive documentation on melt quality. Secondly, it makes new fields of application technically feasible such as developing polymer blends and analysing fibre-filled compounds. In the development of polymer blends, for
example, the company says that inline measuring of full rheological data has not been not possible. Single point melt flow rate can be determined but this gives limited insight and could lead to incorrect conclusions. By delivering decisive viscosity parameters in real time, the company says its inline solution allows polymer blend quality to be analysed inside the extrusion process, enabling it to be adapted and fine-tuned more accurately and quickly than before. This is also the case for analysis of fibre-reinforced compounds. The company says differences between PP fibre-filled compounds can be discerned only when elongational viscosity is established. The Leistritz rheometer was developed with a focus on usability in industry and can be added to and switched between existing compounding extrusion lines (not only those manufactured by Leistritz). This maximises flexibility. It can also be used as a stand-alone solution.
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IMAGE: LEISTRITZ
IMAGE: LEISTRITZ
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