The mineral magnetite (Fe3O4) has been an important raw material for the iron and steel industry for over 100 years. The use of magnetite as a functional filler for plastics and rubbers is relatively new; the first commercial application in polymers was developed in the late 1990s. Magnetite's combination of high density, low scratch visibility and excellent ecological aspects prompted its use as a filler in EVA for the production of automotive sound dampening mats. Further polymer and rubber applications continue to be developed to take advantage of the unique properties of magnetite as a filler material.
Peter L Duifhuis, business manager Polymers of Minelco B.V. and Jos M.H. Janssen of DSM Research describe how specific magnetite grades have been introduced for use in polymers and rubbers and summarize the results of a compounding study of the filler in polyamide and polypropylene undertaken by DSM Research.Different grades of magnetite have been developed for different applications; they mainly differ in particle size (distribution). Table 1 provides an overview of the main properties of three commercial grades.