PROCESS CONTROL | INLINE MEASUREMENT
and the viscosity was corrected in each case using Bagley (entrance pressure loss) and Rabinowitsch Weissenberg. Elongation viscosity and elongation rate were calculated using the Cogswell model from the entrance pressure loss, which is deter- mined by the Bagley correction, and apparent rheological data. Elongation viscosity function determined in this way provides a simple descrip- tion of the visco-elastic processes. The curves for the two LDPE materials measured
at 190°C show the characteristic curve of the strain hardening for the elongation viscosity due to the polymer branches in the test material (Figure 2a and b). Both materials have the same MFR of 4
Table 1: Comparison of the selectivity of melt index, viscosity and elongation viscosity for two LDPE materials
Material
Melt index [g/10 min] Difference [%]
Shear viscosity [Pas] at ý=1/s Difference [%]
Elongation viscosity maximum [Pas] Difference [%]
Source: Göettfert
LDPE1 4 -
5611 -
18600 -
LDPE2 4 0
5006 -10.8
30500 +64%
g/10 min, so cannot be differentiated using the MFR method. Göttfert says the viscosity slope shows only relatively minor differences, but elongation viscosity differs significantly with the second material displaying a much more flexible course of elongation hardening with higher values. Numerical analysis provides a clearer picture, the company says (Table 1). While there is no selectivity for the melt index, extension viscosity shows a clear difference of over 60% as a result of the different branching, whereas the viscosity gives an opposite evaluation. However, shear viscosity correlates with average molecular weight. It says this example shows that a clear material differentia- tion with different molecular weight distribution or branching is possible via elongation viscosity. This has not been detectable through the methods frequently used up to now, such as determination of melt index, the company says.
Leasing options US-based Equitech International has introduced a new leasing scheme with the aim of making its inline UV-Vis colour measurement technology more accessible. The company says that, until now, the cost of in-line colour measurement has been a barrier to companies that have a need to imple- ment this technology in their production lines. It says access to its in-line UV-Vis colour measure- ment technology is now possible for a few thou- sand dollars per month, eliminating the need for capital expenditure. According to Equitech, colour can convey
information indicating the consistency and quality of products. It has long been measured by taking samples from the process line and analysing them using laboratory spectrophotometers. However, offline colour measurement provides information about past events – whether they took place an hour, a shift or a day ago. For example, offline colour measurement cannot detect pulsating feeders, drifting processes and uncontrolled startup phases. The company says the advent of Industry 4.0, machine learning and AI, means that quality control systems will migrate from laboratory analysis to real-time quality assurance, providing information about the current process but also potentially into the future using predictive analytics.
Figure 2a and 2b: Comparison of shear and elongation viscosity measurements between online and laboratory measurements of two different LDPE materials. Source: Göttfert
48 COMPOUNDING WORLD | November 2023
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.colvistec.de �
www.skz.de �
www.sikora.net �
www.goettfert.com �
www.equitechintl.com
www.compoundingworld.com
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