In‐Line Monitoring of Particle Size during Emulsion Polymerization under Different Operational Conditions using NIR Spectroscopy

Abstract

In the present work, the sensitivity of NIR spectroscopy toward the evolution of particle size was studied during emulsion homopolymerization of styrene (Sty) and emulsion copolymerization of vinyl acetate–butyl acrylate conducted in a semibatch stirred tank and a tubular pulsed sieve plate reactor, respectively. All NIR spectra were collected online with a transflectance probe immersed into the reaction medium. The spectral range used for the NIR monitoring was from 9 500 to 13 000 cm−1, where the absorbance of the chemical components present is minimal and the changes in the NIR spectrum can be ascribed to the effects of light scattering by the polymer particles. Off‐line measurements of the average diameter of the polymer particles by DLS were used as reference values for the development of the multivariate NIR calibration models based on partial least squares. Results indicated that, in the spectral range studied, it is possible to monitor the evolution of the average size of the polymer particles during emulsion polymerization reactions. The inclusion of an additional spectral range, from 5 701 to 6 447 cm−1, containing information on absorbances (“chemical information”) in the calibration models was also evaluated.

Stabilizer-Free Dispersion Copolymerization Monitoring by In-Line NIR Spectroscopy

“…35 A recent study from our group on the monitoring of acetic anhydride hydrolysis 30 needed no NIR spectra pretreatments; on the other hand, more complexes systems, such as miniemulsion and emulsion polymerization, required preprocessing. [4][5][6][7][8]12,14,16,17 ■ CONCLUSIONS NIR spectroscopy is an efficient method to monitor the chemical and physical properties of processes. Calibration models can be constructed to monitor properties with fast dynamics and be extended to monitor other systems with fast kinetics.…”

“…Thus, NIR chemometric models require a multivariate calibration. The statistical technique most applied to spectra data treatment is partial least squares (PLS). − ,− ,, In order to construct a calibration model, a training set with known concentration (or conversion, diameter, or any property of interest) is necessary. This property should be analyzed using well-established analytical methods.…”

“…The most common absorption bands in the NIR spectral region to predict polymer conversion of polymerization reactions are between 6200 and 5700 cm –1 , − ,− corresponding to the C–H stretch absorption bands of terminal double bonds present in the residual monomer. Despite the band selection methods available in the literature, the visual band selection method has been the most applied one.…”

“…Particle size analyzers usually require careful sample preparation and are very sensitive to variations in preparation procedures. The most common absorption bands in the NIR spectral region to predict particle size are between 13,000 and 9500 cm –1 − ,, Particle size analyzers have a helium–neon laser at a fixed wavelength of 633 nm (15,798 cm –1 ). The baseline deviation is the main spectral observation in the presence of polymeric particle suspensions.…”

Online Monitoring of the Particle Size in Semibatch Emulsion Copolymerization Using Spatially Resolved Spectroscopy and Raman Spectroscopy

“…Some studies have also employed near-infrared spectroscopy (NIR) to predict the particle size, for instance, in the emulsion polymerization of methyl methacrylate, copolymerization of styrene/butyl acrylate , or copolymerization of vinyl acetate/butyl acrylate, butyl acrylate/styrene miniemulsion copolymerization, dispersion polymerization, styrene suspension polymerization, and vinyl chloride suspension polymerization, where the particle size varies between tens of nanometers to a few millimeters between these systems. These studies demonstrated that the NIR spectrum is affected by the particle size distribution.…”