Impediment effect of two-dimensional graphene on gaseous fluorine permeation during direct fluorination of polyurethane

Abstract

Direct fluorination with gaseous fluorine (F2) is a simple way to prepare fluorine-containing polymers, however, partial hydrolysis of CONH- group during fluorination process often reduces the bulk properties of fluorinated polyurethane (PU). Here, two-dimensional graphene (GE) as barrier layer was introduced into the thermoplastic polyurethane (TPU) matrix followed by fluorination treatment by F2 gas. The conjugated π structure of graphene limited excessive fluoridation of the GE/TPU sample, while the large aspect ratio restrained the diffusion and penetration of F2 gas in the bulk. As a result, rich F elements were accumulated on the surface with the slightly-fluorinated bulk. The fluorinated GE/TPU sample integrated the excellent mechanical properties of TPU with friction behaviors of fluorine-containing polymers. The initial friction coefficient was 0.5, 50% lower than the original GE/TPU while maintaining the unchanged mechanical modulus and thermal stability. This research may effectively solve the issue on performance degradation caused by partial hydrolysis of polymer materials containing CONH- group during fluorination process, providing a simple and effective surface modification strategy for preparing high-performance fluorine-containing TPU.