A process for the preparation of suitable filter aids as polymer blends

A process for the preparation of suitable as a filter aid polymer blends of polystyrene and crosslinked water-insoluble polyvinyl pyrrolidones by processing the two components in an extruder, characterized in that polystyrene is melted in an extruder, then mixed with the polyvinyl pyrrolidone and the mixture of the components 0.1 to 10 wt .-%, based on the total amount of polystyrene and popcorn polymer, is added to water and the mixture is extruded and comminuted.