Processes and compositions for cleaning mixing devices are disclosed that improve the production and quality of thermoplastic polymer resins subsequently produced in the mixing device, while reducing the time needed for cleaning and/or change over. A cleaning mixture comprising polymeric resin pellets having a Rockwell R hardness of 85 to 140 externally coated with an aqueous solution containing sulfonate salts, alkyl aryl sulfonate salts, alkyl sulfate salts, C6 to C36 carboxylic acid salts, or mixtures thereof, is used to purge the mixing device. The surfactant salt is present in the aqueous solution at 0.2 to 30 wt % of the solution, the aqueous solution having a pH of 6.0 to 9.0.