Mass Spectrometry & Spectroscopy
Monitoring concentrations of a polymer blend in real-time by combining extrusion and Raman Spectroscopy
Marek Biermann, Application Specialist, and Dr. Nils Bertram, General Manager, Anton Paar OptoTec GmbH, Seelze-Letter, Germany; Michael Stanko, Product Manager, Anton Paar TorqueTec GmbH, Duisburg, Germany.
Transforming raw plastic materials into fi nished or semi-fi nished products by extrusion is a critical step in the polymer value chain. To optimise this process, in situ monitoring of chemical and compositional changes during polymer extrusion expedites product and process development and enhances quality control to meet customer, application, and regulatory requirements.
Blending of polymers such as polycarbonate (PC) and polymethyl methacrylate (PMMA) is key to achieving the specifi ed mechanical, optical, and thermal properties of fi nal polymer products (e.g. strength, optical clarity, and impact resistance).
The actual properties vary with the relative concentrations of the constituent polymers in the blend. The correct composition needs to be ensured by proper dosing and mixing according to the formulation. This process can be subject to errors – e.g. wrong input materials, operator errors in picking and dosing materials by volume or weight, inhomogeneous mixing, or compromised material integrity.
Controlling the relative concentration of each component during extrusion is crucial to ensuring consistent material properties and to meeting both customer and regulatory acceptance criteria.
In situ process monitoring using Raman spectroscopy enables real-time quantifi cation of polymer composition. This improves analytical effi ciency and eliminates the time lag for offl ine analysis, allowing for immediate corrective action. This is in contrast to offl ine measurements, which pose the risk of disposing of entire batch(es) with nonconformities.
Instrumentation and experimental setup
A fi bre probe from Anton Paar’s Cora 5001 Raman spectrometer was placed directly after the round strand die head of a TwinLab 20/40D twin-screw extruder for real-time measurement of the polymer strand prior to cooling in a water bath and pelletisation.
The Raman system operated at 1,064 nm excitation wavelength, with an exposure time of 9.9 s. Measurements were recorded every 20 s. An averaging feature which automatically takes the average value from three measurements was applied for improved accuracy. Alternatively, measurements can also be done directly inside the extruder die head using Anton Paar’s tailor made extrusion fi ber probe with an 1/2” 20-UNF adapter, as shown in Figure 1. Three relative concentrations were varied over time: 30% PC / 70% PMMA, 50% PC / 50% PMMA, and 70% PC / 30% PMMA.
Results and discussion
When comparing the Raman spectra of PC and PMMA, distinct peaks can be assigned to the corresponding polymers. As visible in Figure 2, clear peaks that are unique to PC can be seen at 706 cm-1 600 cm-1
, 890 cm-1 , 812 cm-1 , 1,452 cm-1 , and 1,730 cm-1
, and 1604 cm-1 .
, while PMMA displays peaks at
Figure 1: Anton Paar’s Raman analyzer Cora 5001 integrated with the Brabender Extruder. In this confi guration, the Raman fi ber probe is directly mounted on the extruder die-head.
Figure 2: Raman spectra of polycarbonate and polymethylmethacrylate.
LAB ASIA - JUNE 2025
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