Enhance interfacial bonding of glass-fiber-reinforced PPS resistance welded joints: mechanisms of surface modification on Ti mesh heating element and ultrasonic assistance

Weak interfacial bonding between the polymer matrix and the metallic heating element (HE) limits further improvement in the lap shear strength (LSS) of resistance-welded joints of glass fiber-reinforced polyphenylene sulfide (GF/PPS). To address this, pure titanium (Ti) meshes modified by micro-arc oxidation (MAO) and γ-aminopropyltriethoxy silane coupling agent (SCA) coupling agent were used as the HE to establish both micromechanical interlocking and molecular bonding between the dissimilar materials. The MAO process generated TiO₂-based surface layers containing microvoids and tunnel-like structures. Fourier transform infrared spectroscopy (FTIR) revealed that hydrogen bonds formed between the –NH₂ groups of the SCA and the C-S bonds of PPS. Simultaneously, interdiffusion occurred between the polysiloxane layer and PPS, resulting in a molecular chain interdiffusion layer (MCIL) at the bonding interface. Energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses demonstrated a synergistic effect between MAO and SCA: MAO increased the hydroxyl group density on the Ti mesh, facilitating SCA grafting, which subsequently elevated surface free energy and improved the wetting and spreading behavior of PPS. This enhanced both mechanical interlocking and interfacial compatibility. Ultrasonic assistance further intensified the strengthening effects of MAO and SCA. The highest LSS of GF/PPS joints, 27.2 MPa, was achieved using Ti mesh treated with both MAO and SCA, representing the highest reported value to date.