Experimental Study of Polymer Degassing in an Agitator Vessel

The present work deals with the experimental investigation of polymer devolatilization in a partial filled agitator vessel with a blade stirrer focusing on film degassing. The apparatus generate a wiped melt film on the barrel wall and a rotating melt pool at the stirrer blade contributing to mass transfer. A model substance system consisting of high-viscous polydimethylsiloxane as polymer and 1,1,2-trichloro-1,2,2-trifluoroethane as volatile is used. The driving force for the degassing is provided by reducing the partial pressure in the gas phase with a gas flow of nitrogen. The concentration of volatiles in the melt is measured by thermogravimetric analysis. The stripped volatiles were recovered and weighted by use of cold traps. The results are evaluated with models based on the penetration theory and surface renewal theory. Experimental measurements indicate that the gas-side mass transfer resistance cannot be neglected. Possible sources of inaccuracy in the execution of degassing studies and their influence on the results are discussed.