Page 58 - Plastics News May 2026
P. 58
TECHNOLOGY NEWS
temperature history, moisture, or contamination While rheological monitoring shows whether the
can push the process outside its validated win- melt behaves as expected, spectroscopy helps
dow. The result may include dimensional varia- confirm that material composition remains within
tion, surface defects, color shifts, or changes in specification. Near-infrared and infrared meth-
mechanical performance. Many of these prob- ods are especially useful for polymer blends,
lems begin upstream, but processors often de- regrind, recycled feedstock, fillers, colorants,
tect them only during offline inspection or down- and additive packages. In these systems, small
stream testing. compositional changes can affect both process-
ability and final properties.
This gap has increased interest in inline melt
monitoring. Two methods stand out: inline rheol- Spectroscopic measurements detect changes
ogy and near-infrared or infrared spectroscopy. in absorption patterns linked to specific chemi-
Rheological indicators track changes in flow be- cal groups or material components. With proper
havior. Spectroscopic methods detect changes calibration, they can estimate blend ratio, track
in composition and molecular structure. Used additive concentration trends, and detect unex-
together, these tools give processors a broader pected material signatures in real time. In prac-
view of melt quality during production and help tice, this helps identify formulation drift, feeder
identify deviations before defects spread. imbalance, carryover from a previous produc-
Inline Rheology as a Process Stability Indicator tion run, or the introduction of an unintended
resin stream.
Inline rheology in industry is evolving rapidly.
While many plants still rely on tracking simpler This capability becomes more important as pro-
viscosity proxies derived from standard process cessors increase recycled content and rely on
data, such as melt pressure, temperature, screw more complex formulations. In these systems,
speed, or throughput, there is an increasing the process may remain mechanically stable for
trend toward deploying dedicated inline instru- some time even when composition has started
mentation. to drift. Spectroscopy can therefore flag a devel-
oping material issue before rheological changes
These specialized instruments, such as vibra- become large enough to affect dimensions or
tional viscometers or slip-stream rheometers, throughput.
operate directly in the melt stream and provide
sensitive, real-time data that goes beyond basic Combining Rheology and Spectroscopy for
process indicators. Better Diagnostics
In extrusion, monitoring often works best near The strongest inline monitoring strategy does
the die, where flow is more stable and easier not rely on a single measurement principle. Rhe-
to interpret. In injection molding, cyclic behav- ology and spectroscopy provide different but
ior makes interpretation harder, but pressure- complementary information, and their combi-
based indicators and cycle-resolved response nation improves both sensitivity and diagnostic
can still provide useful insight. confidence.
A change in both viscosity proxy and spectral
Spectroscopy for Composition and Material
Control signature may indicate a shift in formulation,
blend ratio, or contamination severe enough to
60 PLASTICS NEWS May 2026
