Microwave-Assisted Direct Growth of Carbon Nanotubes at Graphene Oxide Nanosheets to Promote the Stereocomplexation and Performances of Polylactides

Graphene oxide (GO) featuring a two-dimensional (2D) sheetlike structure and extensive oxygen functionalities occupies indispensable research branches in polymer composites. Key to the property translation from GO nanosheets to host polymers is the proper exfoliation and controlled dispersion that are profoundly governed by the competitive evolution between GO-GO intersheet attractions and GO-polymer interfacial interactions. Here, a microwave-assisted synthetic approach was proposed to enable direct in situ growth of carbon nanotubes (CNTs) at GO templates, engendering a minute-level and one-pot route to create three-dimensional (3D) hierarchical nanohybrids (GO@CNT). Featuring a unique 3D structure, the nanohybrids were homogeneously dispersed and properly exfoliated in racemic polylactide (PLA) blends, in clear contrast to microscale local aggregation of GO due to extensive intersheet attractions. Albeit present at an extremely low amount (0.05 wt %), GO@CNT significantly outperformed GO in terms of boosting PLA stereocomplexation, achieving distinct overall improvements in gas barrier performance (oxygen permeability coefficient as low as 0.25 x 10-15 cm3 cm cm-2 s-1 Pa-1) and mechanical properties (tensile strength of similar to 70 MPa and Young's modulus of similar to 2 GPa) for stereocomplexed PLAs. This work affords elucidation of direct covalent functionalization of 2D nanosheets and property-by-morphology understanding in polymer composites, which may motivate further extension to other 2D/one-dimensional (1D) hierarchical hybrids in need for the fabrication of multifunctional polymer composites.