Dynamic mechanical analysis of polypropylene composites based on surface‐treated sepiolite

The dynamic mechanical properties in terms of the storage modulus G′ , loss modulus G″ , and loss tangent δ have been studied for polypropylene‐sepiolite composites. The effect of surface treatment on the relaxation spectra has been elucidated, and quantitative values indicating the extent of polymer‐filler interaction have been given. Analysis of the results show that the addition of sepiolite leads to an increase in the values of the modulus, a value of the glass transition temperature lower than that of unfilled polypropylene, and displacement towards higher temperatures of the α c relaxation associated with the crystalline regions. Surface treatment of the sepiolite, by esterification with organic acids of different chain length, does not have a marked effect on the relaxation spectra of the composites, even though the polymer‐filler interaction parameter decreases with respect to untreated sepiolite.