Karl Fischer Moisture Testing of Recycled Polyethylene Terephthalate
Coulometric Karl Fischer testing with oven desorption at 170 °C isolates true water content in rPET below 50 ppm, preventing costly IV degradation during melt processing.
Background Drift Rate
Meaning
Thermal equilibrium decay represents the baseline loss of heat uniformity within a polymer melt during residence time in the barrel. This background drift rate quantifies the unintended temperature shift occurring when a machine sits in a steady state without injection cycles. It describes the rate of thermal dissipation that occurs through the barrel wall and heaters despite active control loops.
Tooling Stability
Plastic injection moulds depend on the consistency of the heat energy entering the runner system to maintain constant viscosity. The background drift rate creates a delta between the target setpoint and the actual melt temperature at the nozzle tip during extended standby periods. Process engineers adjust the compensation factor to mitigate this discrepancy during production restart phases.
Material Sensitivity
Amorphous resins such as polycarbonate exhibit high sensitivity to the temperature gradients resulting from this drift. A background drift rate that exceeds the tolerance of the material leads to degraded molecular weight or inconsistent shrinkage in the molded parts. Technicians monitor the recovery time required for the sensor array to return to the thermal baseline after a cycle delay.
Economic Consequence
Excessive heat loss drives up electricity consumption as heating elements fight to maintain the standby temperature. The background drift rate governs the scrap percentage generated during the first few shots following an interruption in the production flow. Precise management of this rate allows for smaller process windows and reduces the need for constant gate size adjustments.