A plastic composition containing at least one weakly polar or apolar thermoplastic polymer; at least one metallic salt of an unsaturated aliphatic fatty acid; at least one first mediator which is a hydrocarbon compound having at least one cyclic group and having at least one polar substituent comprising an oxygen atom and/or nitrogen atom, wherein the first mediator comprises at least two cyclic groups per polar substituent, and wherein the melting point of the first mediator is no more than 80° C. below and no more than 50° C. above the melting point of the thermoplastic polymer; and at least one third mediator which is a hydrocarbon compound having at least one cyclic and preferably aromatic group which is unsubstituted or halogen-substituted, wherein the boiling point of the third mediator is no more than 100° C. below and no more than 80° C. above the melting point of the thermoplastic polymer.