Graphene oxide induced isotactic polypropylene crystallization: role of structural reduction
Although graphene oxide (GO) and its derivatives have been demonstrated as effective nucleation agents for semicrystalline polymers, the role of the structural factors was ambiguous. In this study, the effects of structural variation in GO subjected to thermal reduction on crystallization of isotactic polypropylene (iPP) were investigated. The structural integrity of reduced GO, which was regulated by controlling the reduction temperature at a fixed time, was restored due to the decomposition of oxygenic functional groups and the partial recovery of the sp2 carbon network. The crystallization peak of iPP moved to higher temperature with the reduction degree of GO, indicating the higher nucleation activity of reduced GO. Isothermal crystallization results showed that the reduction of GO brought about a stronger acceleration effect on both overall crystallization rate and conformational ordering of iPP. The removal of surface functional groups was considered to facilitate the attachment of iPP chains to stimulate intrachain conformational ordering, and the partial recovery of the sp2 carbon network provided extra nucleation sites for the epitaxial growth of iPP lamellae. They together strengthened the nucleation ability of reduced GO, which was elucidated based on the mechanism of surface-induced conformational ordering. Establishing the relationship between the architecture and nucleation ability of reduced GO makes a pivotal step towards fabricating high performance nanocomposites.