PROCESS CONTROL | INLINE MEASUREMENT
compounds, where elongational viscosity data is important for melt quality settings. Differences between various PP fibre-filled compounds can often only be discerned when this parameter is established, the company says. Leistritz says the inline rheometer has been developed with a focus on useability and can be added to and switched between existing com- pounding lines of any make. It can also be fitted as a stand-alone solution.
Above: A hyperbolic slotted die with intake and
outflow section lies at the heart of the Leistriz system
prises an intake and outflow section, plus two transition zones. In operation, 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 while also preventing expansion, and avoiding pressure swirls and dead areas in the flow channel. The slotted die enables constant monitoring of viscosities with shear rates from 10-10,000 s-1 elongational extension from 5-75 s-1
and . This ensures
that both low and high viscosity polymer melts with or without fillers or reinforcing additives can be analysed. It is also possible to redirect temperature insensitive melts directly into the extrusion process after measurement to prevent material loss (thermally sensitive melts can be channeled out and recovered after measurement).
Application development According to Leistritz, the Inline Elongational Rheometer offers greater accuracy and, compared to melt analysis in the laboratory, provides the ability to capture valid close-to-process data. This allows comprehensive documentation of melt quality in established production processes as well as improv- ing insight into new applications such as develop- ment of polymer blends or fibre-filled compounds. In the development of polymer blends, for
Right: A study carried out by SKZ and ColVisTec aimed to develop an inline system to control colour in recycling of PP
example, Leistritz says inline measurement of full rheological data has not previously been possible. Melt flow rate data can be determined but it represents only one point on the shear viscosity curve and can lead to conclusions that result in waste of material, time and money. Having full rheological data available in real time allows polymer blends to be analysed and fine-tuned more accurately and quickly, it claims. Leistritz says access to full real-time data also
improves quality management by enabling the operator to take immediate remedial action. This can be especially useful in processing of fibre-filled
58 COMPOUNDING WORLD | November 2022 IMAGE: SKZ/COLVISTEC
www.compoundingworld.com
Recycling research German plastics institute SKZ has just concluded a research project with instrumentation specialist ColVisTec exploring ways to improve colour control of recycled plastics materials using a feedback loop. “Only three years remain to achieve rising recycling rates that will be required in the European Union by 2025,” say Franziska Eichhorn and Julia Klein, Team R&D, Experts of Polymer Recycling and Spectroscopy, of SKZ. The researchers say that achieving these high
rates is complicated by the fact that the same quality standards are applied to recycled material as to virgin material, while input material composi- tions can vary regionally and seasonally. “Quality requirements are expected to be met
across an entire batch. For this reason, when colouring compounds, a significant excess of colorant is often used to achieve the desired target colour to obtain a homogeneously coloured re-granulate in every case,” they say. “To reduce this excess, SKZ and ColVisTec have developed a resource-saving and highly economical system solution.” To demonstrate the capability of the new
system, a cascade system was set up on two twin-screw extruders simulating a small-scale recycling plant. Both extruders were coupled to each other via a melt line. The first extruder was used to melt the recycling material, while the
IMAGE: LEISTRITZ
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