Improved strength and toughness of semi-aromatic polyamide 6T-co-6(PA6T/6)/GO composites via in situ polymerization

In this paper, poly(hexamethylene terephthalamide)-co-polycaprolactam (PA6T/6)/graphene oxide (GO) composites were prepared via in-situ polycondensation and/or melt blending. To improve the comprehensive properties, PA6T/6 chains were grafted onto GO, taking advantage of condensation reaction between amino group of the polymer chain terminal and carboxyl group on the GO surface. The results demonstrated that the polymer chain grafted GO reached a more homogeneous dispersion in PA6T/6 matrix compared with pristine GO, which was ascribed to the intermolecular force such as hydrogen bond, generating among amides (CONH) emerged separately on grafted and free PA6T/6 chains. Furthermore, the length of grafted chain was varied by controlling the grafting process and its effect on the thermal and mechanical properties of (PAT/6)/GO composites was studied in detail. Hence, long PA6T/6-chain-grafted graphene sheet gradually improved the tensile strength to 73.6 MPa (by 45.7%) due to strong interaction, excellent dispersion and physical entanglement with PA6T/6 matrix even with a small amount of GO (2 wt‰), and a balance of strength and toughness was obtained owing to the formation of polymer-bridged graphene network structure. Notably, short PA6T/6 (prePA6T/6) chain grafted graphene sheet together with moderate amount of prePA6T/6, which remarkably promoted the crystallization of PA6T/6, might play a synergistic reinforcement role and increased the tensile strength to 71.9 MPa with just 1 wt‰ of GO content. That synergistic reinforcement effect might open a new avenue to further enhance those graphitic carbon-based polymer nanocomposites with extremely small amount of fillers, especially for those crystallizable polymers.