IN-PROCESS MEASUREMENTS FOR MONITORING AND CONTROL OF GELATION LEVELSIN UPVC COMPOUNDING

The rheology of carefully prepared commercial unplasticised poly vinyl chloride (UPVC) formulation has been studied under actual process his tory using an in-line rheometer die and a computer monitored single sc rew extruder, and the results compared with those observed for off-lin e characterisations of gelation levels in the unplasticised PVC. It is observed that the in-process results are capable of being used to pre dict accurately the gelation level of the product, expressed as 'grade s'. Steady state and dynamic responses of the processing line were als o studied using similar in-line measurements, which has led to an algo rithm for real time closed loop control of gelation based upon melt te mperature and melt pressure in the die and extruder screw speed.