Thermal and rheological properties of polyamide 6/layered double hydroxide clay composites

Thermal and rheological properties of polyamide 6/layered double hydroxide (PA6/LDH) composites were studied. Pristine (U-LDH) and organically modified (M-LDH) clays were used in this study. Some evidence of intercalation was observed on the microstructure of PA6/M-LDH samples, while PA6/U-LDH was characterised by microcomposite morphology as shown by the transmission electron microscopy results. The scanning electron microscopy results showed a complete delamination of the M-LDH in the PA6 matrix while U-LDH was evenly dispersed as immiscible tactoids. In the melt state, the M-LDH had a significant influence on the melt microstructure of PA6 matrix when compared to U-LDH. Differential scanning calorimetry results, both dynamic and isothermal experiments, showed that LDH had a heterogeneous nucleating effect on the PA6 matrix, with the U-LDH showing better nucleating effect when compared to M-LDH. The thermogravimetric analysis results showed that M-LDH had a negative influence on the thermal stability of the composites, while U-LDH improved their thermal stability. The X-ray diffraction and dynamic mechanical analysis results showed that the presence of M-LDH promoted the formation of γ-crystallites in the PA6 matrix, while U-LDH composites were dominated by the α-crystallites. This phenomenon had a positive correlation with increasing content of both LDH clays. An overall improved dynamic mechanical properties were observed for PA6/U-LDH when compared to PA6/M-LDH composites.