Crystal structure evolution of nylon 6/GO_graft nanocomposites during heat treatments and cold drawing

The effects of graphene oxide (GO) on the crystallization and crystal structures of nylon 6/nylon 6-grafted graphene oxide (GO_graft) nanocomposites (NGO) during heating, cooling, and cold drawing experiments were studied with in situ wide- and small-angle X-ray scattering measurements at a synchrotron radiation source, and compared to those of pure nylon 6. For the liquid-nitrogen-quenched samples, the small concentration of GO_graft in the nylon 6 matrix (0.0045 wt %) induced the formation of α-phase nylon 6, while the pure nylon 6 exhibited the β phase. The degree of crystallinity and long period of the NGO increased from 10.0 to 17.5 % and from 7.31 to 10.6 nm, respectively, as the GO_graft content increased from 0 to 0.045 wt%. During the heating process, the α phase of the NGO changed to a new β phase at approximately 150 °C through a Brill transition, and then to a high-temperature α′ phase at around 195 °C. On the other hand, the initial β phase of the nylon 6 only transformed into the high-temperature α′ phase at 192 °C. When stretched at room temperature, both the β phase of the virgin nylon 6 and α phase of the NGO were transformed into a metastable phase, and the fraction of this metastable phase increased at the expense of the β (or α) phase.