A control scheme for filament stretching rheometers with application to polymer melts

We propose a new control scheme to maintain a constant strain rate of the mid-filament diameter in a filament stretching rheometer for polymer melts. The scheme is cast as a velocity algorithm and consists of a feed-back and a feed-forward contribution. The performance of the controller is demonstrated on a commercial low-density polyethylene. Several strain rates and experimental conditions are tested to demonstrate the necessity of the control parameters and the limits of both the control scheme and the experimental apparatus. When the control parameters are properly tuned, the algorithm ensures that the applied strain stays within 2% of the set point and measurements can be made up to Hencky strains of 6.5.

► A control algorithm for achieving constant uniaxial deformation in FSR is proposed.
► The control algorithm consists of a feed-forward and a feed-back contributions.
► The applied strain stays within 2% of the set point up to Hencky strains of 6.5.
► This algorithm permits measurements not accessible to the current integral methods.