Ethylene tetrafluoroethylene (ETFE) is a partially fluorinated copolymer of ethylene and tetrafluoroethylene. ETFE is a melt processable polymer, designed to have high corrosion resistance and strength over a wide temperature range. Some key quality parameters that should be monitored during the production of fluorinated polyolefins are melt flow rate (MFR) and moisture content. The measurement of these parameters usually involves using chemicals and can be time-consuming. Near-infrared spectroscopy (NIRS) offers users rapid and reliable prediction of key quality parameters in ETFE without any sample preparation or cleaning procedures.
273 ETFE pellet samples with varying MFR and moisture content were measured on a Metrohm near-infrared spectroscopic analyzer in reflection mode. All measurements were performed in rotation using a large sample cup to reduce the stray light effect caused by varying particle sizes. An overlay of the sample spectra is displayed in Figure 1.
The obtained NIR spectra (Figure 1) were used to create a prediction model for quantification of MFR and moisture content in ETFE. The quality of the prediction model was evaluated using correlation diagrams (Figures 2 and 3), which display a high correlation between the NIR prediction and the reference values. The respective figures of merit (FOM) display the expected precision of a prediction during routine analysis.
| Figures of Merit | Value |
|---|---|
| R2 | 0.9413 |
| Standard Error of Calibration | 0.96 g/10 min |
| Standard Error of Cross-Validation | 0.98 g/10 min |
| Figures of Merit | Value |
|---|---|
| R2 | 0.840 |
| Standard Error of Calibration | 0.011% |
| Standard Error of Cross-Validation | 0.012% |
This Application Note demonstrates the feasibility to determine mechanical properties and perform moisture analysis in fluorinated polyolefins like ETFE using NIRS. In comparison to the standard analytical methods (Table 1), quality control with NIR spectroscopy shows obvious advantages regarding the analysis time. In addition, the sample handling with near-infrared spectroscopy is easier to perform and safer since no chemicals are needed.
| Parameter | Method | Time to result |
|---|---|---|
| Melt flow rate | Melt flow indexer | ∼20 min (measurement and cleaning) |
| Moisture | Karl Fischer titration | ∼3–5 min |
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