Measurement of the true melt temperature in a twin-screw extrusion processing of starch based matrices via infrared sensor

• An inline method for the calibration of an infrared sensor to biopolymeric melts is developed.
• A new infrared sensor is verified at the transient non-isothermal extrusion conditions.
• The performance of the IR-sensor is compared to conventional sensors (i.e. thermocouples).
• IR sensor is capable of capturing the temperature variations and the maximas.
• Increasing screw speed leads to higher temperature maximas at constant barrel temperature.

True temperature distribution in extruded melts is a crucial information for food extrusion applications, in which the material transformations and reactions can otherwise not be fully controlled. Conventional measurements by thermocouple are known to be critical as response time is long and measured data are influenced by surrounding. Infrared sensors offer the advantage of quick response time in the form of a non-invasive probe to measure the temperature distribution. However, infrared sensors need to be calibrated on the material to be investigated. For this purpose, an inline calibration method was developed and verified. The results show that neither the extrusion conditions at the range investigated nor the matrix type (i.e. starch or wheat flour) have a significant influence on the surface and volumetric emissivity of biopolymeric melt. Furthermore, the infrared sensor was verified in a twin screw extruder and the results are compared to the measurements by a conventional thermocouple. The infrared sensor was able to capture the temperature variations generated by rotation of screws.