EXTRUSION OF RECYCLED POLYMER FEEDSTOCKS

The increased emphasis on the use of recycled feedstocks has brought i n the need for continuous on-line monitoring of process conditions. Th is is done in an effort to detect process shifts and react accordingly to maintain optimal conditions. Time series analysis is ideal for on- line modelling of continuous processes employing recycled feedstocks, as the disturbances present in the feedstock can be quantified using t his approach. The models obtained can then he employed for closed loop control of the process. The closed loop control allows for maximizing of the amount of recycled material, yet ensuring an acceptable finish ed product. This work presents a study of the stochastic dynamics of t he extrusion of recycled feedstocks. Both ''in-house'' and ''post-cons umer'' feedstocks are considered. Process outputs include the extrudat e thickness and diameter, the head pressure, the melt temperature and the flowrate. The process inputs are the die gap and the level of recy cle material. Process and disturbance transfer function models are obt ained. Control simulations are performed on the process and disturbanc e models to ascertain the feasibility of a closed loop system for main taining of optimal process conditions. A minimum variance controller ( MVC) is employed in the simulation. The response of the closed loop sy stem to various disturbance inputs is monitored. The control scheme re sults in a much lower offset from the set point for the case with MVC than for the case with no control.