Novel Heating Elements for Induction Welding of Carbon Fiber/Polyphenylene Sulfide Thermoplastic Composites

Conductive films of carbon nanofibers (CNFs) decorated/coated with metals, either silver (Ag) or nickel (Ni) are fabricated using a solution casting process and used as novel heating elements (HEs) for induction welding of carbon fiber/polyphenylene sulfide (CF/PPS) thermoplastic composites. Prior to making the films, the metal-coated CNFs are prepared by an electroless plating method using Ag or Ni precursors. A solution of the metal-coated CNFs is then casted onto a pure PPS film to give a robust conductive film upon solvent evaporation and annealing in an oven at 200 degrees C. SEM observation and electrical resistivity measurements reveal that the CNFs are successfully coated with the metals which result in a significant decrease of the films' electrical resistivity. A third type of HE is also fabricated by solution mixing Ag-coated CNFs and magnetic Fe3O4 nanoparticles. The welding efficiency of the fabricated films is assessed for induction welding of two different types of thermoplastic composites, that is, unidirectional pre-impregnated 16 plies of CF/PPS compression-molded in a quasi-isotropic stacking sequence and 8-ply of satin weave fabric CF/PPS compression-molded in a cross-ply stacking sequence. The mechanical apparent lap shear strength (LSS) of the induction-welded joints is evaluated for the fabricated HEs and compared with the LSS of joints welded using conventional stainless steel mesh susceptors. Under similar testing conditions, Ag-coated CNFs HEs lead to the highest LSS with an average value of approximate to 31.5MPa. In general, the new HEs result in superior LSS and higher heating rates when compared to the metallic mesh counterparts. The present work offers a new perspective to push the boundaries toward high quality welding of thermoplastic composites using nanomaterials-based HEs.