Role of poly(ethylene glycol) grafted silica nanoparticle shape in toughened PLA-matrix nanocomposites

In order to study the effect of nanoparticle shape on the mechanical properties of polymer-matrix composites, two types of poly(ethylene glycol) (PEG) grafted silica nanoparticles, i.e., nanoplatelets and nanospheres, with similar surface characteristics are prepared through biomimetic synthesis. These two nanoparticles are then incorporated into amorphous poly(D,L-lactide) (PLA for short) as nano-fillers. SEM images confirm the uniform distribution of polymer grafted nano-fillers in PLA-matrix. The tensile tests results show that the elongation-at-break of nanoplatelets/PLA is almost twice as high as that of nanospheres/PLA at the loading level of 1.8-2.4 vol %, indicating that nanoplatelets have much more significant toughening effect than nanospheres. The following comparative analysis demonstrated that two nanoparticles exhibit different behaviors during shear yielding of PLA, leading to different ways of energy dissipation and toughening. In addition, the creep behaviors and dynamic mechanical properties are also closely related to the shape of nanoparticles.