Effects of annealing (solid and melt) on the time evolution of polymorphic structure of PA6/silicate nanocomposites

The effects of annealing including solid-state annealing (190 °C) and melt-state annealing (230 and 250 °C) on the polymorphic behavior and thermal property of polyamide 6 (PA6)/layered-silicate nanocomposites (PA6LSN) have been investigated as a function of annealing time using Modulated Differential Scanning Calorimetry (MDSC) and wide angle X-ray diffraction. For comparison, thermal behavior and polymorphism of pure PA6 were also studied. It was demonstrated that PA6LSN and PA6 exhibited a similar polymorphic behavior when they were annealed in the solid state for different time duration. As the annealing temperature was elevated to 230 and 250 °C, significant differences in thermal behavior and polymorphism between PA6LSN and PA6 could be found. For example, the γ phase became the absolutely dominating for PA6LSN, while the α crystal was the most predominant phase in neat PA6. Moreover, a new endothermic peak is observed around 235 °C in all PA6LSN MDSC scans, which might be related to the melting of PA6 lamellae formed in the confined environment on the surface of the nano-silicate.