Method for producing blends consisting of polystyrene and of a cross-linked polyvinyl pyrrolidone having a reduced styrene residual monomer content

1. A process for removing residual styrene monomers from blends comprising polystyrene and water-insoluble, crosslinked polyvinylpyrrolidone, via treatment with water, which comprises carrying out the treatment on a particulate solid blend.

2. The process of claim 1 , wherein the particulate blend is composed of polystyrene and a popcorn polymer and is mixed with water, the mixture is subjected to a steam distillation process, and then the particulate blend is isolated.

3. The process according to claim 2 , wherein the mixture passed to the steam distillation process is prepared from blend and water in a ratio by weight of from 1:2 to 1:10.

4. The process according to claim 2 , wherein following the steam distillation process, the particulate blend is isolated via filtration and is dried.

5. The process according to claim 2 , wherein said steam distillation process is carried out at temperatures of from 100 to 120 ° C.

6. The process according to claim 2 , wherein following the steam distillation process, a pulverulent blend is obtained via spray drying.

7. The process according to claim 2 , wherein the particulate blend composed of polystyrene and of a popcorn polymer is mixed with water, and the water is directly drawn off from the mixture in a heatable container equipped with an apparatus for moving the composition.

8. The process according to claim 7 , wherein said heatable container used, provided with an apparatus for moving the mixture, comprises a paddle dryer.

9. The process according to claim 7 , wherein the mixture from which the water is directly drawn off has a ratio by weight of blend to water of from 1:1 to 3:1.

10. The process according to claim 7 , wherein the mixture has a ratio by weight of blend to water of from 1:1 to 2:1.

11. The process according to claim 7 , wherein the treatment in which the water is directly drawn off from the mixture takes place at temperatures of from 90 to 105° C.

12. The process according to claim 1 , wherein said blend comprises from 50 to 90% by weight of a polystyrene and from 10 to 50% by weight of a water-insoluble crosslinked polyvinylpyrrolidone.

13. The process according to claim 1 , wherein said polystyrene present in the blend comprises standard polystyrene, polystyrene modified with rubber so as to be highly impact resistant, or a styrene-butadiene copolymer.

14. The process according to claim 1 , wherein said polystyrene present in the blend comprises standard polystyrene.

15. The process according to claim 1 , wherein the content of residual styrene monomers is lowered to less than 20 mg/kg, based on the total weight of said blend.

16. The process according to claim 1 , wherein the content of residual styrene monomers is lowered to less than 10 mg/kg, based on the total weight of said blend.

17. A particulate blend composed of a polystyrene and a water-insoluble crosslinked polyvinylpyrrolidone, with a residual styrene monomer content of less than 20 mg/kg, obtained by a process according to claim 1 .