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Graphene films receive tremendous attention due to their ultrahigh electrical and thermal conductivities, which show great application prospects in modern electronic devices. However, the brittleness and low strength of graphene films largely limit their use in advanced applications. And the preparation processes of graphene films reported so far are also not completely green. In this work, a novel strong and green graphene composite film with outstanding electromagnetic interference shielding effectiveness (EMI SE), electrical and thermal conductivities was successfully fabricated by using nanofibrillated cellulose (NFC) as dispersing agent and mechanical compression. In this way, graphene nanosheets (GNs) were not only efficiently dispersed in the aqueous solution but also linked together by NFC to enhance mechanical strength of the prepared films. Simultaneously, mechanical compression could powerfully induce strong alignment and increase the contact area of the GNs. As a result, the optimum electrical and thermal conductivities of the obtained films reached up to 988.2 S cm–1 and 240.5 W m–1 K–1, respectively, along with a high tensile strength of 61 MPa and a superior EMI SE of 43 dB with only ≈13 μm in thickness. Even more, the resultant films revealed excellent flame resistance. And the NFC can be removed by burning the films, resulting in complete graphene films with much higher electrical and thermal conductivities. The manufacturing route in our study is facile, cost-effective and completely green for the preparation of strong and highly conductive graphene-based thin films.
Yang et al. (Fri,) studied this question.