Thermal history dependence of polymorphic transformation of polyamide 6/silicate nanocomposites

BACKGROUND: Although much research has been devoted to nanocomposites of polyamide 6 (PA6) with inorganic nanoparticles, most research has mainly focused on the effects of clay and annealing temperature on the crystallization behavior of the PA6 matrix, but the effect of annealing on the thermal behavior of PA6/clay nanocomposites remains an interesting subject which requires further investigation. This paper focuses on the effects of thermal history on the polymorphic transformation of PA6 and PA6/layered silicate nanocomposites (PA6LSN). RESULTS: It was found that PA6 and PA6LSN exhibit a similar polymorphic behavior when they were annealed at 190 °C. As the annealing temperature was elevated to 230 and 250 °C, significant differences in polymorphic transformation and thermal behavior between PA6 and PA6LSN could be observed. For example, the γ phase became the dominant crystalline phase for PA6LSN samples while the α crystal was still the predominant phase in neat PA6. Furthermore, a higher temperature endothermic peak observed at around 236 °C in all PA6LSN modulated differential scanning calorimetry scans was also found to be strongly dependent on the cooling rate and annealing temperature. CONCLUSION: The thermal history has a strong influence on the polymorphic transformation of PA6 and PA6LSN. For the first time, the effect of thermal history on the high‐temperature endothermic peak of PA6LSN was investigated and it was observed that this peak is also strongly dependent on the thermal history.