In-line dielectric sensor for chemical composition measurements in molten polymers

Resin producers and compounders use additives to extend and modify the properties of their polymers, and as processing aids in the production of plastics, elastomers, fibers, adhesives and coatings. They need to measure the concentrations of these additives so they can meet demanding product quality specifications and boost their manufacturing efficiency. Near-infrared spectroscopy has been successfully applied [1] for measuring certain additives, but it is restricted to optically transparent materials. Few other techniques exist for inline composition measurements in polymer melts. Dielectric measurements have also been successfully applied for measuring additive concentrations in polymer melts [2], and interdigitated dielectric sensor designs [3] have proven very reliable with thermosets [4] and thermoplastics. The dielectric sensor described here incorporates a flow-through design that generates no back pressure or flow obstructions. Theory and experiments indicate that dielectric measurements in melts can quantitatively determine individual or total additive concentrations with standard uncertainties that depend on electrical contrast and can be smaller than a volume fraction of 0.1 percent (1000 ppm) with polymers and compounds having one or possibly two dominant additives.