In-line monitoring of polymer processing using fiber-optic spectroscopy

This research was focused on developing fiber optic molecular spectroscopic techniques to provide information about chemical compositions and rheological properties (such as melt index and complex viscosity) of polymer melts in polymer processing. With the development of fiber optics, chemometrics, and the advent of powerful desk computers, in-line spectroscopic analyses have proven to be effective and non-destructive ways of providing real-time measurements of polymer melts, and have already found application in process monitoring. In this research, near infrared (NIR), ultraviolet-visible (UV-Vis), and Raman scattering spectroscopy have been applied to an in-line extrusion process for simultaneous measurements of compositions and rheological properties of flowing molten polymers.

Fiber optic NIR and UV spectroscopic systems have been improved and applied to the in-line monitoring of polymer additives in polymer processing. A methodology is proposed for the feasibility of measuring the concentrations of multiple additives in polypropylene and polyethylene. It was found that the characteristics of absorption bands of polymer additives in NIR and UV spectroscopy depend on their chemical structures and chromophore groups. Slip agents and hindered amine light stabilizers with >NH and -NH₂ groups show strong NIR spectral bands. Thus, concentrations of additives with either of the above two groups can be determined by fiber-optic NIR spectroscopy. Conjugated unsaturated chromophores show strong and distinguished peak bands in the UV region. Thus, concentrations of additives with benzene rings or other kinds of conjugated groups in their chemical structures can be determined by the fiber-optic UV spectroscopy.

In the prediction of rheology of polymer melts, polyethylene with erucamide and Armostat 310® and poly(ethylene vinyl acetate) (EVA) were studied. The effect of erucamide and Armostat 310® on the melt index of PE was investigated. Calibration models were built for the simultaneous measurements of concentrations of the above two additives and melt index of PE using NIR and UV spectroscopy, respectively. For the EVA copolymer system, a fiber-optic Raman scattering system was applied to the in-line monitoring of the concentration of vinyl acetate and rheological properties (melt index and complex viscosity) of EVA melts in an extrusion process.

In the development of instrumentation, robust NIR transmission probes were applied to fiber-optic NIR spectroscopy system. A dual-beam fiber optic UV spectroscopic system was designed and evaluated, and the transmission efficiency of UV light was improved by UTK-designed UV probes for the determination polymer additives. For Raman scattering spectroscopy, a plane-polarized fiber optic Raman scattering spectroscopic system was applied to make simultaneous measurements of composition and rheological properties of poly(ethylene-vinyl acetate) (EVA) in extrusion.