Challenge in Manufacturing Nanofibril Composites with Low Matrix Viscosity: Effects of Matrix Viscosity and Fibril Content

•The viscosity ratio and second phase concentration have significant effects on the nanofibril morphology.•High aspect ratio fibrils are formed with low viscous PP at high PET content.•The physical network is formed in nanocomposite with limited amount of nanofibrils.•Crystallization behaviors and mechanical properties are enhanced.