Droplet Bridging Effect in Polymer/Polymer/Filler Ternary Composites

In particle-filled polymer composites with selective distributions of fillers in one phase, much attention has been focused on the "volume exclusion effect" in reducing the percolation threshold of filler, while the role of dispersed polymer phase acting as bridges of fillers in the particle network has largely been ignored. Herein, we studied industrially important ternary composites, polypropylene (PP)/ethylene-octene copolymer (a polyolefin elastomer, POE)/talc systems, and adopted rheology to reveal the bridging behavior of POE droplets in the network of talc particles. It is found that talc fillers concentrate in the PP phase using the "blend first" protocol, while more talc particles are located at the interface of PP and POE phases using the "filler first" protocol. Changing the POE viscosity and talc size can affect the migration of talc from the POE phase to the PP phase in the "filler first" protocol. The linear rheology behavior indicates that besides the "volume exclusion effect", the talc-POE hybrid network can further contribute to the reinforcement effect. Meanwhile, the POE droplet bridging structure can facilitate the rebuilding of the hybrid network after large amplitude oscillatory shear, in contrast to the un-recoverable structures in the PP/talc binary composites. The correlation between rheology and selective distribution of fillers in ternary composites may provide practical guidance for processing and designing advanced polymer composites with controlled selective location of fillers.