Effects of acid- and diamine-modified MWNTs on the mechanical properties and crystallization behavior of polyamide 6

The acid- and diamine-modified multi-walled carbon nanotubes were characterized by XPS, apparent density test and SEM. Their effects on the mechanical properties and crystallization behavior of polyamide 6 (PA6) were comparatively investigated via SEM, DMA, tensile test and DSC. It was revealed that acid treatment could effectively induce polar oxygen-containing groups on the surface of MWNTs, which was beneficial for MWNTs to combine with polar PA6 matrix. However, the interactions such as the hydrogen bonds among the acid-modified MWNTs caused a compact stacking morphology, resulting in a worse dispersion in PA6 matrix. Further diamine modification on the acid-modified MWNTs could graft diamine molecules onto the surface of MWNTs, which weakened the interactions among the MWNTs and thus resulted in a less compact stacking morphology compared with acid-modified MWNTs. Therefore, a better dispersion and a stronger interfacial adhesion of MWNTs in PA6 matrix could be obtained with diamine-modified MWNTs. The storage modulus, glass transition temperature, yield strength, Young's modulus and crystallization temperature of PA6 were found to be improved significantly by the incorporation of diamine-modified MWNTs.