Flexible and densified graphene/waterborne polyurethane composite film with thermal conducting property for high performance electromagnetic interference shielding

High-performance electromagnetic interference (EMI) shielding materials with flexibility, excellent mechanical property, and thermal conductivity are highly desired for fifth-generation communications devices. Graphene exhibits tremendous potential due to its high electrical conductivity and unique lamellar structure. However, the construction of densified graphene structure in polymer matrix is still challenging. Herein, we develop a graphene/waterborne polyurethane (G/WPU) flexible film with densified and ordered layer-structure for using as an EMI shielding material. By virtue of the polyvinylpyrrolidone modified strategy and facile liquid phase ball-milling treatment, the graphene nanosheets can be efficiently dispersed into the WPU substrate and tightly connected between each other via internal interactions. Benefiting from the relatively low defects and densified structure of graphene, the resultant G/WPU film yields a high electrical conductivity of 1,004.5 S/m, and a tensile strength of around 48.5 MPa. As a consequence, it achieves an average EMI shielding effectiveness of over 30 dB in the X-band with a thickness of merely 0.15 mm and the value is further enhanced to 73.4 dB at 0.9 mm with a low density of 1.4 g/cm³, offering over 99.99999% shielding of incident electromagnetic waves. More importantly, this G/WPU film also exhibits a high cross-plane thermal conductivity of about 1.13 W/(m·K). Thus, this work develops a high-performance EMI shielding material with both good capacity of heat transmission, but also provides a facile strategy for designing next-generation advanced, lightweight, flexible, and multifunction shielding materials.