Fig. 4: SEM images of PLA fracture surface with and without nanoparticles.

a PLA with 1.3 wt.% of 200 nm silica NPs—zoom-in of fracture surface inside the spherical hole left by a detached spherulite (marked square in the wider-area inset). Holes left by individual nanoparticles and some of their clusters are seen, as well as numerous gaps between packets of lamellar crystals created by the intercalated NPs. Note that if the NPs were evenly distributed throughout the sample volume, they would have occupied only 0.7 % of the surface. b The same for PLA without NPs for comparison; the surface is markedly smoother.