Enhanced electrical and mechanical properties of graphene nano-ribbon/thermoplastic polyurethane composites

In this study, graphene nano-ribbon (GNR) was synthesized by unzipping multi-walled carbon nanotubes (MWCNTs). The electrical conductivity, dielectric properties, electromagnetic interference (EMI) shielding effectiveness (SE) and mechanical properties of GNR/thermoplastic polyurethane (TPU) and MWCNT/TPU composites were thoroughly investigated. GNR/TPU composite exhibited a significantly enhanced electrical conductivity of 1.9 × 10−4 S/cm, three orders of magnitude higher than MWCNT/TPU composite (1.1 × 10−7 S/cm). The dielectric properties of GNR/TPU composite were also superior to those of MWCNT/TPU composite. At 8.2 vol%, the real permittivity of GNR/TPU composite was 298, while 108 was measured for MWCNT/TPU composite. The use of GNR consequently amplified EMI SE. The EMI SE of GNR/TPU composite was 24.9 dB, which is considerably greater than that of MWCNT/TPU composite (9.3 dB) at 8.2 vol%. By unzipping MWCNTs, the point-to-point contact is converted to area-to-area contact, which significantly boosts contact area. The number density of fillers also increased due to exfoliation of MWCNT. The changes on contact interfaces of fillers and an increase in number density resulted in an improved electrical conductivity and a high real permittivity, which led to augmented EMI SE. In addition, the reinforcing effect of GNR is much greater than that of MWCNTs. Young’s modulus of the GNR/TPU composite was 37 MPa while 12.7 MPa was measured for the MWCNT/TPU composite at 8.2 vol% loading. The GNR/TPU composite also exhibited a superior tensile strength of 19.6 MPa at 5.3 vol% while the MWCNT/TPU composite reached 17.8 MPa even at a higher loading of 8.2 vol%. This is mainly due to the higher surface area of the GNR induced by unzipping and exfoliation of the nanotubes, and the formation of edge structures in GNR that increase the adhesion between filler and matrix.