Reinforcement and toughening of polypropylene/organic montmorillonite nanocomposite using β-nucleating agent and annealing

In this work, a β-phase nucleating agent (NA) was introduced into polypropylene/organic montmorillonite (PP/OMMT) nanocomposite to adjust the crystalline structure of PP matrix, and the injection-molded bars were annealed at different temperatures. The evolution of crystalline structure was characterized by using differential scanning calorimetry, wide angle X-ray diffraction. The effect of annealing on the nucleated nanocomposite was evaluated by measurement of the tensile, impact, and dynamic mechanical properties. The results show that, although OMMT inhibits the formation of β-PP, the crystallization of PP matrix in the nucleated nanocomposite is mainly determined by β-NA and large amounts of β-PP are induced accordingly. Annealing induces the further variation of crystalline structure of matrix, which is greatly dependent upon the annealing temperature. Specifically, annealing at higher temperature (150 °C) leads to the partial exfoliation of OMMT. Furthermore, both the modulus and the fracture resistance of nucleated nanocomposite are greatly improved by annealing. Therefore, this work hints that the simultaneous strengthen and toughening of PP nanocomposites can be achieved through the introduction of β-PP and annealing.