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

Abstract Polymer/polymer-nanofibril composite is considered as a new member of the polymer composite family. With its superior property and easy processability, this type of composite shows a bright future together with the emerging polymer nanocomposites, which typically involve inorganic nanofillers, carbon-based nanofillers, or cellulose-based nanofibers. Although the dispersion of the nanofibrils in the polymer matrix is easier than the cellulose nanofiber composite case, there are great challenges in controlling the fibril morphology of polymer/polymer-nanofibril composite. The goal of this study is to elucidate the influences of the matrix viscosity and the reinforcement content on the nano-phase morphology. The results show that a PP with lower melt flow rate (MFR) was better for generating higher aspect ratio and smaller diameter PET nanofibrils across a broad concentration range. The diameter of fibrils from a higher MFR PP decreased with increasing PET concentration. The study found that the coalescence and morphology change in the nanofibrillation process depends on both the matrix viscosity and the reinforcement (PET) concentration. The oscillatory shear behavior of composites with different nanofibril morphologies was also examined. Differential scanning calorimetry (DSC) and polarized light microscopy (POM) were used to study the changes in the crystallization kinetics of the various PP/PET-fibril composites. The presence of nanofibrils also significantly improved the mechanical properties of the composites. The results provide a deep insight into the fundamental aspects of manufacturing nanofibrillation composites, especially the conditions under which second phase coalescence is promoted.