Mechanical spectroscopy of polymer-magnetite composites

Mechanical properties of magnetite (Fe3O4) filled polypropylene (PP) prepared in an extrusion and injection molding process were investigated. Various grades of magnetite were used. Mechanical spectroscopy was performed in a temperature range from 173 to 428 K with frequencies from 10−1 to 102 Hz, and the crystallinity of test samples was estimated. Damping spectra show an α peak of the principal relaxation (∼285 K) at the glass transition temperature, a relaxation β-peak (∼220 K) attributed to local motions in the amorphous phase and an α′-peak (∼365 K) attributed to the relaxation in crystalline parts of the polymer. These peaks correspond to drops of the storage modulus. peak is decreased by the extrusion process while the α′-peak is increased compared to not extruded PP. At high temperatures a drastic increase of the loss factor superposes the α′-peak for higher filler loadings. The crystallinity of the polymer matrices varies between 25 and 37%. At low temperatures the storage modulus increases with an increase in the magnetite fraction. The used particle size distributions show no significant influences on the storage moduli for temperatures from 173 to 285 K, whereas for temperatures above 285 K smaller mean particle sizes lead to higher storage moduli and lower loss factors.