Monitoring end groups and viscosity in polyester melts

Brearley etal.9 at DuPont (Wilmington, DE, USA) used in-line transmission NIR to monitor carboxyl end groups and DP in PET oligomer and pre-polymer melt streams in a new polyester process. The business value was derived from several sources. 

First and most important, real-time NIR monitoring enabled real-time control of the process. For a given product, the molecular weight and end-group balance in the prepolymer exiting the front end or melt part of the process must be controlled at specified levels in order for the back end or solid-phase part of the process to successfully produce the intended polymer composition. In addition, the variability in pre-polymer composition must be controlled with very tight tolerances to keep the variation in final product composition within specification limits. Since the process dynamics in the front end were more rapid than those in conventional PET processes, the conventional analytical approach involving off-line analysis of samples obtained every 2-4 hours was not sufficient to achieve the desired product quality. 

Second, real-time monitoring enabled particularly rapid development of process understanding, by providing otherwise-unattainable information on process dynamics and by 

Finally, real-time NIR monitoring, once validated to the satisfaction of the process engineers and operators, significantly reduced the need for hot process sampling (with its attendant safety concerns) and lab analysis by allowing the sampling frequency to be greatly reduced (to near zero for some process points). 

Step 1 Include fouled spectra in the calibration data set. 

Second, real-time monitoring enabled particularly rapid development of process understanding, by providing otherwise-unattainable information on process dynamics and by drastically reducing the time needed to carry out designed experiments (since it was no longer necessary to remain at a given process state for several hours until several lab results indicated that the process was lined out). 

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