Non-isothermal melt-crystallization and mechanical properties of titanium(IV) oxide nanoparticle-filled isotactic polypropylene

The present contribution reports an investigation on the effect of the addition of titanium(IV) oxide (TiO2) with diverse surface characteristics [i.e. neat, silica (SiO2)-coated and stearic acid-coated] and various contents (ranging from 5 to 30 wt%) on non-isothermal melt-crystallization, subsequent melting behavior and mechanical properties of filled isotactic polypropylene (iPP). The cooling rate used ranged between 5 and 30 °C min−1.The crystallization exotherm for all of the samples investigated became larger and shifted towards a lower temperature as the cooling rate increased. The crystallization peak temperature (Tp) values for all of the iPP samples filled with neat TiO2 nanoparticles were slightly greater than those of the neat iPP and were not affected by the variation in the filler content. For iPP samples filled with stearic acid-coated TiO2 nanoparticles, the Tp values were not much different from those of the neat iPP. For iPP samples filled with 5, 20, and 30 wt% SiO2-coated TiO2 nanoparticles, marked differences in the Tp values in comparison with those of the neat iPP were observed. Together with the Avrami analysis, the nucleation ability of the various fillers investigated can be ranked as follows: SiO2-coated TiO2 nanoparticles >neat TiO2 nanoparticles >stearic acid-coated TiO2 nanoparticles. Lastly, the presence of the nanoparticles caused the rigidity of the resulting composites to increase (especially when the filler content was greater than or equal to 20 wt%.