Key factors in mechanical reinforcement by double percolation network: Particle migration and shear stability of filler network

The improvement of the mechanical performances of poly(propylene carbonate) (PPC) was successfully implemented in a two-step mixing by constructing double percolation networks, i.e., nano-fillers (NF) forms continuous network in poly(lactic acid) (PLA), and PLA/NF composites form co-continuous morphology in PPC. Four kinds of nano-fillers (hydrophilic/hydrophobic nanofiber/nanosilica) were chosen to reveal the key factors in the two-step mixing process on how to control the efficiency of the reinforced network as well as the strength of filler network. It is found that the strength of filler network in the first step, intensity of mixing in the second step, selective distribution of nano-filler are three key factors to construct strong filler network. The strength of filler network in the first step determines the network strength in the final composites, and the shear stress in the second mixing step determines how much the formed filler network can be kept, while the thermodynamically preferred distribution and migration determines the amount of filler that can take part in the formation of network. These key factors can serve as a general guide to construct double network in two-step mixing.