The rheology of carefully prepared commercial unplasticised poly vinyl chloride (UPVC) formulation has been studied under actual process history using an in-line rheometer die and a computer monitored single screw extruder, and the results compared with those observed for off-line characterisations of gelation levels in the unplasticised PVC. It is observed that the in-process results are capable of being used to predict accurately the gelation level of the product, expressed as 'grades'. Steady state and dynamic responses of the processing line were also studied using similar in-line measurements, which has led to an algorithm for real time closed loop control of gelation based upon melt temperature and melt pressure in the die and extruder screw speed.
