Fluorescence based temperature measurements and applications to real-time polymer processing

eal-time temperature and pressure measurementsof polymer resins have been the backbone of proc-ess monitoring for many years. For temperature meas-urements, both thermocouple and infrared radiometertransducers have been commercially available for in-sertion into standard instrumentation ports on proc-essing machines. It is well known that experimentaldifficulties are experienced with both measurements(1–3). For example, when a melt thermocouple probe ispositioned in the barrel of an extruder, the machinebarrel temperature dominates its response because heattransfer from the barrel to the thermocouple junctionis much more efficient than is heat transfer from resinto thermocouple. Phenomena such as shear heatingand large temperature profiles in the resin flow streamare not seen because the large thermal mass of themachine damps the response of the thermocouple. In-frared radiometry can yield accurate resin tempera-tures for transparent resins of known emissivity, butproblems exist for the calibration of this instrumentshould the resin emissivity change such as with afilled resin.The inadequacies of temperature measurements havemajor implications regarding rheological understand-ing of the process and the onset of resin degradationtemperatures. To address these issues we have en-gaged in a program to use fluorescence spectroscopyas a tool for monitoring resin temperature duringprocessing. The hardware of the measurement appa-ratus involves an optical fiber sensor that is insertedinto existing instrumentation ports and is used totransmit excitation light to the resin and to collect theresultant fluorescence and transmit it to the detector(4, 5). Fluorescence is produced from a dye that ismixed with the resin at dopant concentrations, lessthan 10