Use of dielectric loss to determine blend time for organic polymer solutions

When scaling up mixing applications, it is often important to measure blend time. In our application, we need to measure blend time in nonaqueous solutions of organic polymers in pilot‐ and plant‐scale steel tanks. Techniques employing visual observations can be used in small‐scale glass or Plexiglas tanks, but these methods are not applicable to large‐scale operations. Another standard technique is to measure conductivity of a tracer material, which is useful particularly for aqueous systems, but does not provide an adequate response for our system. A new technique that we established involves the measurement of the dielectric loss of a tracer material added to an acrylic polymer solution in mineral oil. It is demonstrated that the addition of N,N‐dimethylformamide (DMF) results in mixing curves that give blend times equivalent to those measured by visual methods. Our preliminary studies were performed in a 2‐L vessel over a temperature range of 30–120°C. The magnitude of the dielectric loss measurement is shown to depend on the scanning frequency of the measurement and the temperature of the polymer solution. The variation over a small temperature range is slight and will not interfere with the measurements.