Flexible and flame-retarding thermoplastic polyurethane-based electromagnetic interference shielding composites

A flexible and flame-retarding thermoplastic polyurethane (TPU)-based electromagnetic interference (EMI)-shielding composite with multilayered structure was fabricated via coextrusion technology. The layer multiplication could not only create numerous layer interfaces, but also tailor the selective distribution of flame retardants (FRs) and carbon nanotubes (CNTs) endowing each extrudate excellent flexibility. When the layer numbers reached 32, synergistic flame-retarding and EMI-shielding multiple functional networks were generated and performed the optimum comprehensive performances, overcoming the major disadvantage of the conventional composites where the networks may breakup each other. Due to the interfacial polarization loss caused by the impedance difference between conducting and flame-retarding layers, the maximum shielding effectiveness (SE) of 38.5 dB was obtained with less than 4 wt% CNTs. Besides, superior flame retardancy rated by V-0 with quick self-extinguishment and low heat release was achieved owning to the production of continuous and foaming carbonaceous structure among layers. More significantly, the SE of the char residue, which was less concerned in conventional composite systems, was even beyond 60 dB. The maintenance of the multilayered architecture and the generation of atmosphere cavities were regarded to benefit for providing numerous impedance-mismatched interfaces and extending the transmission path of the microwaves. Consequently, the multilayer-assembled strategy was proposed to balance the mechanical, flame-retarding and EMI-shielding performances for satisfying with the stringent requirements of protective materials.