Effective method for the synthesis of pimelic acid/TiO2 nanoparticles with a high capacity to nucleate β-crystals in isotactic polypropylene nanocomposites

Functionalized titanium dioxide (TiO2) nanospheres with pimelic acid (TiO2–PA) were synthesized through a novel and effective route, where the goal was to promote a high percentage of β-crystal into a matrix of isotactic polypropylene (iPP) by the use of low amount of nucleating agent. The successful chemical attachment of pimelic acid onto the TiO2 surface was indicated by the presence of a new band at 1575 cm−1 and an increase in the thermal stability of the PA of approximately 200 °C, which were observed through infrared spectra and thermogravimetric techniques, respectively. The iPP nanocomposite was analyzed by differential scanning calorimetry and wide-angle X-ray diffraction in order to identify β-crystals. An exothermic peak at 152 °C and a diffraction peak at 2θ = 16.2° confirmed the ability of the TiO2–PA nanoparticles to promote the β-crystal phase in the iPP nanocomposite even at low percentages (0.1 % w/w).About 85 % of β-crystal content was promoted with the TiO2–PA particles, that was significantly higher than the 25 % obtained by unmodified TiO2 particles. Moreover, from visco-elastic analysis, it is evident that TiO2–PA particles help to improve the dissipation energy by effect of the promoted β-crystal phase in the polymer composites. Likewise, the AFM images provide evidence of the incompatibility of TiO2 particles with the iPP matrix showing protruding reliefs in comparison with the homogeneous topography of the iPP/TiO2–PA composite. This results were confirmed by SEM, where the exclusion of TiO2 particles was evident.