Percolation Network Formation in Nylon 6/Montmorillonite Nanocomposites: A Critical Structural Insight and the Impact on Solidification Process and Mechanical Behavior

The incorporation of montmorillonite (MMT) into Nylon 6 can endow advantages like improved mechanical strength and thermal stability, making Nylon 6/MMT a possible ideal alternative for Nylon 66. However, the relationship between the microstructure and physical properties of nylon 6/MMT nanocomposites is unclear so far due to the complicated system, including the highly asymmetric geometry of the exfoliated MMT layer and the complicated interaction between MMT layers and entangled nylon 6 chains. Herein, we focus on two processes, namely the impact of MMT on the solidification procedure during molding and the toughness–brittleness transition during the tensile stretch, in order to elucidate the structure–property relationship of nylon 6/MMT composites. We firstly studied the solidification process of nylon 6/MMT with bending height experiments. The results showed that the solidification process occurs prior to the crystallization of nylon 6, indicating that a physical crosslinked network rather than a crystalline structure is the reason for the solidification process. Furthermore, the solidification speed has a step change at around 2 wt% MMT content, indicating that the MMT percolation network is related to the transition. We further studied the influence of MMT inclusion on the mechanical properties, and found the tensile strain at break showed a similar step change at around 2 wt% MMT content, which further confirms the existence of an MMT percolation network above 2 wt% MMT content. It was generally believed that the main effect of MMT on nylon 6 is the nanofiller enforcement; we found that the percolation effect of the highly asymmetric 2-D nanofiller plays a central role in influencing the mechanical properties and solidification behavior during molding.