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.