Applications of in-line fiber optic raman spectroscopy to polymer processes

Process monitoring is an essential part of ensuring the final product quality in a manufacturing process. In-line monitoring is developing at a fast pace as the method of choice as compared to the off-line monitoring techniques due to its advantages such as lower cost and lower waste. It also eliminates the sample preparation and handling concerns associated with the polymeric processes. In this research, in-line monitoring techniques were developed for emulsion polymerization and extrusion processes using fiber-optic Raman spectroscopy. Varying product quality from batch to batch and the residual monomer content are important concerns in the emulsion polymerization reactions. The kinetics of the batch emulsion polymerization were studied for the methyl methacrylate (MMA) and vinyl acetate (VA) polymerization. The Raman spectroscopy was also used to monitor changes in the reaction rate due to varying comonomer content (AA) for copolymerization of 2-ethylhexyl acrylate (2-EHA) with acrylic acid (AA). For the extrusion processes, a thorough study of the poly(ethylene vinyl acetate) (EVA) random copolymers was performed. Rigorous multivariate analysis was used to develop robust calibration models for quantification of VA concentrations. Rheological properties, such as melt index (MI) and complex viscosity (|η*(ω)|) of the EVA and polypropylene (PP) samples were monitored in real time using polarized Raman spectroscopy