Viscosity online monitoring

During a homogenous (bulk or solution) polymerization reaction, both the concentration of polymer and molar mass change and hence viscosity should also change. Therefore, online monitoring of the viscosity could give... 

Rotational (torque measurements) or capillary process viscometers, as well as ultrasound and tube oscillations [58] can be used to measure viscosity online during a polymerization reaction. The first two techniques have been widely applied in the monitoring of both chain growth polymerizations and step-growth polymerizations. 

Reed and coworkers [59, 60] were the first to develop a robust polymerization setup to online monitor reduced viscosity in free-radical and hving polymerization. The methodology developed by the authors is based on the continuous extraction and dilution of a small sheam from the reactor on which measurements are being made while it flows though a multidetector platform. Among the detectors used, a single... 

Torque measurements have been used for online monitoring of the viscosity of polymerization reactions. The advantage of the torque measurement as compared with that of the capillary is that no treatment (dilution and flow) of the reaction medium is needed. Several examples of monitoring chain-growth polymerization reactions [62, 63] and step-growth polymerization reactions (specially curing reactions) can be found in the hterature [64]. 

Dietrich T, Ereitag A, Schlecht U. New micro viscosity sensor—A novel analytical tool for online monitoring of polymerization reactions in a micro reaction plant. Chem Eng J 2010 160 823-826. 

The physical meaning of viscosity was discussed in Chapter 5. In the online monitoring context, a very simple and robust means of measuring total dilute solution viscosity, rj, is with a single capillary viscometer. With a measurement of the pure solvent viscosity, and knowledge of the polymer concentration, c, the reduced viscosity, is given by... 

Mignard E, Guerret O, Berlin D, Reed WF. Automatic Continuous Online Monitoring of Polymerization reactions (ACOMP) of high viscosity reactions. Polym Mat Sci Eng 2003 88 314-316. 

Monitoring Acrylamide Polymerization Time-dependent signatures for conversion, reduced viscosity, and molecular weight during continuous online monitoring of acrylanude polymerization under a variety of temperature, and initiator conditions were compared in Reference [3]. 

FIGURE 12.7 Automatic Continuous Online Monitoring of Polymerization Reactions detectors response (LS90 ° and viscosity) to the different components of the diluted, phase inverted polyacrylamide emulsion (top) determination of dissolution time, from RI data for polyacrylamide in emulsion and in dry form. Reprinted (adapted) with permission from Alb AM, Farinato F, Calbick J, Reed WF. Online monitoring of polymerization reactions in inverse emulsions. Langmuir 2006 22 831-840. 2006 American Chemical Society. 

Additionally, online monitoring methods have been developed to adapt off-line characterization methods into in situ (i.e., in-reactor) probes for determination of kinetics and monomer conversion with optical methods such as mass spectroscopy (MS), ESR, FTIR, near IR, and Raman spectroscopy. However, frequently, due to high turbidity and viscosity of the polymer reaction milieu, the optical surfaces are easily fouled, leading to frequent sensor failure. Furthermore, data acquired with these probes are model dependent the empirical and inferential calibration schemes used can be expensive and time consuming to develop and can drift and become unreliable as reactor conditions change and as sensors become fouled. Another limiting feature of these methods is that they usually measure only one characteristic of the reaction, such as monomer conversion and are not directly sensitive to polymer molecular mass and intrinsic viscosity. More detailed discussion of these techniques can be found in Chapters 6-10 of this book. 

Online monitoring of viscosity is currently used in industry. Despite the fact that useful rheological characterization of materials requires a wide range of shear rate measurements. 

Kim JS, Lee DG, Online cure monitoring and viscosity measurement, J Mater Proc Technol, 37(1-4), 405-416, 1993. 

FIGURE 13.10 Approach to the steady state of and/with fits according to Equations 13.22 and 13.35. The inset shows the approach to steady state of reduced viscosity t]. Data are excerpted from one of the steady-state approaches in Figure 13.8. Adapted with permission from Grassl B, Reed WF. Online polymerization monitoring in a continuous tank reactor. Macromol Chem Phys 2002 203 586-597. 

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