In-line Analysis of EVA Copolymers using Vibrational Spectroscopy

1. IRC polymer engineering UNIVERSITY OF BRADFORD In-line Analysis of EVA Copolymers using Vibrational Spectroscopy S.E.Barnes, M.G.Sibley, H.G.M.Edwards#, I.J.Scowen# and P.D.Coates IRC in Polymer Science & Technology, School of Engineering, #Dept. of Chemical and Forensic Sciences, University of Bradford

2. Outline • Context • In-line Instrumentation • Aims and objectives of current research • Results • Data manipulation • Conclusions • Future work • Acknowledgements

3. Context • High level of interest into on-line / in-line analysis of polymer processing • increased demands on quality of polymeric materials / products • Immediate detection of problems during processing • optimises operating conditions • saves energy • reduces waste • reduces need for off-line testing

4. Process spectroscopy • Multi-probe measurements • NIR + ultrasound • Raman + ultrasound • Raman + NIR • Enhanced monitoring • molecular specificity • towards real time • non-invasive • non-destructive • Process analysis • blends • additives • decomposition • reactive extrusion

5. Applications • Continuous monitoring for • polymer characterisation • analysis of polymer blends / co-polymer composition • additive identification / quantification • shear induced orientation studies (polarised Raman) • degradation / process induced change • reactive extrusion

6. In-line techniques

7. 1 to 11mm Path length 38mm bore In-line Transmission NIR • fibre-optic transmission probes - samples across melt section • variable path length from 1 to 11 mm • wavenumber range 8500 - 4000 cm -1 (1200-2500 nm) • resolution 2-16 cm -1

8. Raman Spectroscopy Hololab RXN-2 analyser, Kaiser Optical Systems • 300 mW , 785 nm laser • CCD detector • 3 channels • 5 cm-1 resolution • In-line fibre-optic probe with sapphire window • focal distance - 2.5 mm - point measurement • Dynisco type fitting

9. Current Research Extrusion of a series of ethylene vinyl acetate (EVA) random co-polymers Comparison of the response and sensitivity of in-line Raman and NIR as well as ultrasoundto alterations in Vinyl acetate (VA) concentration

10. Experimental setup • Materials • EVA copolymers with varying VA content between 2 – 44% wt • VA content of each copolymer determined by TGA analysis

11. Experimental setup • Process parameters • Betol BC38 single screw extruder • screw speed 15 rpm • extrusion temperature 180C • Instrument set-up • NIR - 3 mm path length, 4 cm-1 resolution, 8000 to 4000 cm-1 • Raman – 1 spectrum per minute; 28 second exposure,1 accumulation • Real-time monitoring during extrusion • NIR – relative intensity of IR active spectral features • Raman – integrated area of Raman active spectral features • ultrasound transit time • Melt temperature and pressure measured

12. Sensor arrangement Single screw extruder with Raman, NIR, ultrasound, P and T sensors

13. Raman results In-line Raman spectra of PEVA (3010 - 450 cm-1) Spectral region 1800 to 550 cm-1 chosen for multivariate analysis

14. Raman results Change in Raman spectrum (2000 cm-1 – 500 cm -1) during extrusion of EVA copolymer samples (2 % - 43.1 % wt VA)

15. Raman results Change in integrated peak area of O-C=O def. feature at 629 cm-1 during extrusion

16. NIR results NIR absorbance spectra showing first overtone and combination band region of EVA copolymer melts Spectral region 6200 to 5080 cm-1 chosen for multivariate analysis

17. NIR results C-H stretch of VA 3D plot showing alterations in NIR spectral features during extrusion of EVA copolymers

18. Ultrasound Results Alteration in Ultrasonic transit time and melt pressure during sequential extrusion of EVA copolymers Melt pressure in the die varied throughout the extrusion process, due to variation in viscosity (MI values) Alteration in transit time is not linear with pressurevariation

19. Ultrasound vs Raman Response of transit time and integrated area of feature at 629cm-1 to alteration in VA content

20. Multivariate analysis : Grams PLSIQ • multivariate techniques • partial least squares regression (PLS) • principle component analysis (PCR) • model spectral variation in a calibration data set • calibration for all constituents in multi-component systems • whole spectrum / selected spectral areas used for calibration • no pre-treatment of spectra is necessary

21. Data manipulation • 15 spectra of each copolymer in PLS-IQ calibration • first derivatives of the spectra to eliminate: • NIR baseline shifts • Raman fluorescence and background noise • data mean centred to enhance subtle differences between spectra • specific regions of the spectra were chosen for the model • NIR - 6030-5080 cm-1 • Raman - 1800 to 550 cm-1 • PLS1 used to produce a calibration

22. Raman Results PLS1 results showing comparison of predicted against actual VA percentage (one factor model) Standard error of calibration = +/- 0.56 % VA (1σ) R2 = 0.99

23. Raman Results Predicted against actual VA percentage for independent spectral data set Standard error of prediction +/- 0.67 % VA R2 = 0.991

24. Raman Results True and predicted values for VA content in EVA copolymers

25. NIR Results PLS results showing comparison of predicted against actual VA percentage (one factor model) Standard error of calibration = +/-0.604 %VA (1σ) R2 = 0.9981

26. NIR Results Predicted against actual VA percentage for independent spectral data set Standard error of prediction = +/-0.631 %VAR2 = 0.998

27. NIR Results True and predicted values for VA content in EVA copolymers

28. Ultrasound R2 = 0.971 Change in ultrasonic transit time with VA content; comparison of three sets of experimental data • Extruder operated at 15 rpm during Tests 1 and 3 ; 10 rpm during Test 2 • Ultrasonic transducers removed and repositioned after test 1 difference transit time between data in test 1 and tests 2 and 3

29. Conclusions • In-line prediction of wt % VA content has been successfully conducted using in-line Raman NIR and Ultrasound • PLS analysis has been applied to Raman and NIR data to build multivariate successful calibration models. • A successful PLS model for the Raman region 1800 – 550 cm-1 was produced with an SEP value of 0.67 %wt VA (one principal component). • The NIR region 6030-5080cm-1 was used to construct a PLS model with an SEP of 0.63 %wt VA for a one-factor model.

30. Conclusions • Ultrasonic transit time is dependent upon melt density and bulk modulus, which change with %wt VA. • Ultrasound is highly sensitive to changes in VA content of the copolymer resins. The repeatability of the ultrasonic data is shown to be excellent.

31. Future work: Raman / NIR • further analysis of EVA copolymers using various NIR path lengths • in-line Raman and NIR to evaluate MI during polymer extrusion • qualitative and quantitative analysis of polymer additives • Raman and NIR to monitor reactive extrusion processes • melt orientation studies – polarised Raman

32. Future work:Fluorescence • implementation of new in-line, variable focus fluorescence probe • fluorescence for the quantitative analysis of polymer additives. • melt temperature measurement using fluorescent probes • temperature dependant dyes Lens tube and fibre optics inserted into outer casing of in-line fluorescence probe

33. Acknowledgements IRC polymer engineering UNIVERSITY OF BRADFORD • Dr Elaine Brown / IRC colleagues • IRC and EPSRC for support of research studentships • AT Plastics inc. for the kind donation of the copolymers • RAPRA for TGA analysis • CPACT for the opportunity to present