(265c) Twin-Screw Extruders for Solvent Devolatization from Polymers

Wiped Film Evaporators (WFE’s) are used extensively in the chemical and polymer industry for bulk as well as trace devolatization of solvents from the final product. The energy from the externally heated walls, along with the shear heat and surface renewal from the internal rotating blades is used to remove the solvents. However, in case of polymer products with high viscosity which require a high operating temperature, the WFE’s can result in degradation and/or discoloration of the product due to the high residence time and temperature.

To overcome these disadvantages a twin-screw extruder was used for the trace devolatization of solvent from a high viscosity polymer. The presentation covers the theoretical comparison of WFE’s with extruders in terms of residence time, shear rate, surface renewal and vacuum capability. An overview of the pilot testing that shows the effect of key control variables such as feed rate, extruder screw RPM, barrel temperature, and vacuum on vent ports on the response variables such as specific mechanical energy, molecular weight build, color build and residual solvent in the final product is provided. The switch from WFE’s to a twin-screw extruder for trace solvent devolatization resulted in higher production rates as well as improved quality in terms of color, residual solvent content, particulate count and overall product consistency. The key learnings could be applied to similar high viscosity polymeric systems.