Application of ultrasonic radiation for the development of polypropylene/multi-walled carbon nanotubes nanocomposites and its effect on the PP chemical degradation

The effects of ultrasound on the chemical structure of polypropylene (PP) and its composites with different MWCNT content were investigated. The PP composites with 0%, 1%, 3%, and 5% (by weight) MWCNT were extruded using a traditional single-screw extruder and immediately US irradiated in a static mixer. The chemical structure of PP was characterized by using FTIR, DSC, TGA, and GPC to determine any changes caused by the ultrasound, and the MWCNT structure by scanning electron microscopy (SEM). The PP/MWCNT composites were characterized using Raman spectroscopy, DSC, TGA, and SEM, and tested for tensile properties, thermal stability, and electrical and thermal conductivity. The results showed that ultrasonic irradiation caused a slight oxidation in the PP structure and a 13% reduction in its molecular weight. An increase in PP crystallinity, attributed to the improved nucleating effect of the nanotubes, was also observed as a consequence of ultrasonic irradiation. The sonicated PP/MWCNT composites exhibited better dispersion of nanotubes within the PP matrix, resulting in a 30% increment in the elasticity modulus, 45 °C higher for thermal decomposition, an 11 orders of magnitude enhanced volume resistivity, and a 25% increment in thermal conductivity. Furthermore, the SEM results showed that the MWCNT structure was maintained during processing, thanks to the low shear stresses provided by the single-screw extruder, but keeping dispersion with the ultrasonic static mixer.

Graphical abstract