An assembly strategy of polylactic acid (PLA)-SiO₂ nanocomposites embedded in polypropylene (PP) matrix

The aim of this work is to evaluate the effect of adding different amounts of SiO₂ nanoparticles (NPs) during the synthesis of polylactic acid (PLA) and polypropylene (PP) blends on the proccesability. The analysis was carried out in terms of the morphological, rheological and mechanical properties as well as their potential applications for packaging. To reach this goal, it was initially realized an optimization of sol–gel parameters to produce of SiO₂ NPs with a particle size <20 nm. Thereafter, different quantities of SiO₂ NPs (1, 2, 3, 5 wt.%) were incorporated into PLA matrix through melt mixing process to achieve pellets and finally, it was realized the polymer blend to produce PP_100-x (PLA-SiO₂)_x nanocomposites (x = 5, 10 and 20 wt.%, of PLA-SiO₂ pellets). It was found that the addition of SiO₂ into PLA matrix improves the crystallinity percentage, from 10 to 77 %, depending on the SiO₂ quantity; however, it also restricts the movement of PLA chains favoring a viscous behavior. A high dispersion of PLA-SiO₂ systems into PP matrix was obtained in composites containing 1 wt.% of SiO₂. The presence of inorganic nanostructures modified the dipole–dipole interaction between organic components affecting the microstructure and thermal stability (lower T_d). The observed interaction and high dispersion with low amounts of SiO₂ NPs (1 wt.%), led to improve the interfacial miscibility, which in turn enhanced the mechanical properties in the PP₉₀(PLA-SiO₂)₁₀ nanocomposites, compared to PP and PLA. The results indicate that at the end of product shelf-life, this composition can promote a faster degradation in contrast with pure PP and PP-PLA composites.