Abstract: The present invention relates to a filled polymer composition comprising polyethylene, polypropylene and an ultrafine calcium carbonate-containing filler material surface-treated with a surface-treatment agent, which has a total amount of carbon atoms from C4 to C34 and comprises at least one carboxyl group and/or a derivative thereof. The present invention further relates to a process for producing said filled polymer composition, the use of the surface-treated calcium carbonate-containing filler material for improving the mechanical properties of a polymer composition comprising polyethylene and polypropylene, as well as an article comprising the inventive filled polymer composition.

Abstract: The present invention relates to a kit of parts comprising a surface-treated calcium carbonate-containing filler material and a peroxide agent for improving the mechanical properties of a polymer mixture comprising at least one polyethylene polymer and at least one polypropylene polymer, a filled polymer mixture, a process for the preparation of a filled polymer composition, a filled polymer composition obtained thereby or obtainable by reacting the filled polymer mixture, the use of a surface-treated calcium carbonate-containing filler material and a peroxide reagent for reacting a polymer composition comprising at least one polyethylene polymer and at least one polypropylene polymer, preferably thereby improving the mechanical properties of the polymer composition, as well as an article comprising the filled polymer mixture or the filled polymer composition.

Abstract: The present invention refers to a surface treated filler material product comprising a) at least one calcium carbonate-containing filler material and b) a treatment layer on the surface of the at least one calcium carbonate-containing filler material comprising i. maleic anhydride grafted polyethylene and/or maleic anhydride grafted polypropylene and ii. at least one hydrophobizing agent. Furthermore, a process for preparing the inventive surface treated filler material product is disclosed, as well as a polymer composition comprising at least one polymeric resin and the inventive surface treated filler material product.